Infectious Disease and Microbiology – Flavimonas oryzihabitans

Overview

Flavimonas oryzihabitans is a rare aerobic Gram-negative bacillus that acts primarily as an opportunistic pathogen. Reported infections are often healthcare-associated and have a notable relationship with intravascular catheters and implanted prosthetic devices.

An important clinical presentation is catheter-associated bacteremia, which may be polymicrobial.

Microbiologic Characteristics

Flavimonas oryzihabitans is:

• An aerobic Gram-negative bacillus

• An uncommon human pathogen

• Primarily associated with opportunistic and healthcare-related infections

The organism has undergone taxonomic reclassification and is now generally known as Pseudomonas oryzihabitans.

Epidemiology

Human infection is rare.

When infection occurs, it is frequently associated with patients who have:

• Intravascular catheters

• Prosthetic devices

• Peritoneal dialysis catheters

• CNS shunts

• Significant underlying medical conditions

These associations suggest that foreign material and disruption of normal host barriers can facilitate infection.

Bacteremia

One of the most important manifestations is bacteremia.

Bloodstream infections may be:

• Polymicrobial

• Associated with intravascular lines

• Healthcare-associated

When the organism is repeatedly isolated from blood in a patient with an intravascular catheter, a catheter-related bloodstream infection should be considered.

Intravascular Line Infection

Intravascular catheters provide a potential surface for bacterial colonization and subsequent bloodstream invasion.

The clinical pattern may be:

Intravascular catheter

• ●

Fever or systemic illness

• ●

Positive blood cultures for F. oryzihabitans

→ Consider catheter-associated bacteremia

Peritoneal Dialysis-Associated Peritonitis

F. oryzihabitans has been reported as a cause of peritonitis in patients undergoing peritoneal dialysis.

Patients may develop:

• Abdominal pain

• Fever

• Cloudy peritoneal dialysis fluid

• Increased inflammatory cells in dialysate

The dialysis catheter may serve as an important portal or persistent source of infection.

CNS Shunt Infection

The organism can infect central nervous system shunts.

Such infections demonstrate its ability to cause disease involving implanted medical devices.

Depending on the clinical situation, management may require both antimicrobial therapy and evaluation of the infected shunt.

Prosthetic Joint Infection

F. oryzihabitans has occasionally been associated with prosthetic joint infection.

Possible manifestations include:

• Joint pain

• Swelling

• Reduced joint function

• Local inflammatory findings

Because prosthetic material is involved, antimicrobial therapy alone may not always provide adequate source control.

Prosthetic Valve Endocarditis

Rare cases of prosthetic valve endocarditis have also been described.

This represents a serious invasive manifestation and should be considered when persistent bacteremia occurs in a patient with a prosthetic cardiac valve.

Meningitis

F. oryzihabitans can rarely cause meningitis.

Diagnosis depends on compatible clinical findings and microbiologic isolation from cerebrospinal fluid or other relevant specimens.

Wound Infection

The organism has also been recovered from wound infections.

Its significance should be interpreted according to the clinical appearance of the wound and the quality of the specimen because an unusual environmental organism recovered from a superficial specimen does not necessarily establish invasive infection.

Diagnosis

Diagnosis is established by:

Culture of the organism

Depending on the clinical syndrome, specimens may include:

• Blood

• Peritoneal dialysis fluid

• Cerebrospinal fluid

• Joint or prosthetic material

• Wound specimens

For significant infections, antimicrobial susceptibility testing can help guide therapy.

Treatment

The source lists an:

Antipseudomonal β-lactam

as a treatment option.

It also lists the carbapenems:

• Imipenem

• Meropenem

Treatment should be individualized according to the infection site, severity, and susceptibility results.

Additional Treatment

Additional agents listed in the source include:

• Ciprofloxacin

• Aminoglycosides

Because this organism is an uncommon pathogen, susceptibility-guided antimicrobial selection is particularly important.

Device-Associated Infection

A major clinical theme is the organism’s association with foreign or prosthetic material:

Intravascular line

Peritoneal dialysis catheter

CNS shunt

Prosthetic joint

Prosthetic heart valve

This association should raise consideration of device-related infection when the organism is recovered from an appropriate clinical specimen.

Source Control

When an implanted device is the suspected source, treatment may require consideration of:

• Catheter removal

• Shunt revision or removal

• Management of infected prosthetic material

• Drainage or debridement when appropriate

The need for device removal depends on the location, severity, persistence of infection, and clinical circumstances.

High-Yield Clinical Pattern

Hospitalized or medically complex patient

• ●

Intravascular catheter or implanted device

• ●

Gram-negative bacillus

• ●

Bacteremia, often polymicrobial

→ Consider Flavimonas oryzihabitans (Pseudomonas oryzihabitans)

Exam Essentials

Organism: Flavimonas oryzihabitans

Current name: Pseudomonas oryzihabitans

Type: Gram-negative bacillus

Oxygen requirement: Aerobic

Frequency: Rare human pathogen

Major infection: Catheter-associated bacteremia

Bacteremia: Frequently polymicrobial in the source

Other infections: Peritoneal dialysis-associated peritonitis, CNS shunt infection, prosthetic joint infection, prosthetic valve endocarditis, meningitis, wound infection

Major association: Indwelling and prosthetic medical devices

Diagnosis: Culture

Treatment in source: Antipseudomonal β-lactam or carbapenem

Additional agents: Ciprofloxacin or aminoglycoside

Management principle: Consider susceptibility-guided therapy and appropriate device/source control

Key clinical pearl: Flavimonas oryzihabitans, now generally called Pseudomonas oryzihabitans, is a rare opportunistic Gram-negative bacillus with a strong association with intravascular lines and other prosthetic devices; catheter-associated, sometimes polymicrobial, bacteremia is a particularly characteristic presentation.

Infectious Disease and Microbiology – Fasciolopsis buski

Overview

Fasciolopsis buski is a large intestinal trematode (fluke) that causes fasciolopsiasis. Unlike Fasciola species, which primarily involve the liver and biliary tract, F. buski primarily inhabits the small intestine.

Infection is concentrated in parts of South and Southeast Asia and usually produces gastrointestinal manifestations. Heavy worm burdens can rarely result in acute intestinal obstruction.

Microbiologic Characteristics

Fasciolopsis buski is:

• A trematode helminth

• An intestinal fluke

• Approximately 7 cm long as an adult

• One of the largest intestinal flukes infecting humans

Adult worms primarily inhabit the small intestine.

Epidemiology

Fasciolopsiasis occurs predominantly in:

• Rural Southeast Asia

• India and other parts of South Asia

Transmission is associated with areas where the parasite’s freshwater life cycle can be maintained.

Transmission

Humans acquire infection by ingesting metacercariae attached to raw or inadequately prepared aquatic vegetation.

Freshwater snails serve as intermediate hosts.

The general transmission cycle is:

Eggs reach freshwater

→

Freshwater snail intermediate host

→

Metacercariae develop on aquatic plants

→

Humans ingest contaminated aquatic vegetation

→

Adult flukes develop in the small intestine

Fasciolopsiasis

The disease caused by F. buski is known as:

Fasciolopsiasis

The severity of disease is related partly to the number of worms present.

Light infections may produce few or no symptoms, whereas heavier infections can cause significant gastrointestinal disease.

Gastrointestinal Manifestations

Clinical manifestations may include:

• Diarrhea

• Constipation

• Vomiting

• Anorexia

• Abdominal discomfort

The parasites can produce local irritation and inflammation of the intestinal mucosa.

Heavy Infection

Heavy parasite burdens can produce more severe gastrointestinal manifestations.

Large numbers of these relatively large flukes may interfere with normal intestinal function.

Acute Intestinal Obstruction

A rare but important complication is:

Acute intestinal obstruction

This is particularly associated with a heavy worm burden.

Thus:

Endemic-area exposure + gastrointestinal symptoms + intestinal obstruction

should raise consideration of heavy F. buski infection.

Diagnosis

Diagnosis is primarily established by:

Parasitologic examination of stool

Characteristic trematode eggs can be detected microscopically.

Stool Examination

Stool microscopy is the principal diagnostic method because adult worms residing in the intestine release eggs that are passed in feces.

The eggs may resemble those of Fasciola species, so clinical and epidemiologic context can assist with interpretation.

Treatment

The source recommends:

Praziquantel 25 mg/kg orally every 8 hours for 1 day

Praziquantel is the major antiparasitic agent associated with treatment of fasciolopsiasis.

Additional Treatment

The source lists:

Niclosamide 2 g orally as a single dose

as an additional treatment option.

Prevention

Prevention centers on interrupting transmission from contaminated freshwater environments.

Important measures include:

• Avoiding raw aquatic vegetation in endemic areas

• Thoroughly cooking aquatic plants

• Safe sanitation and disposal of feces

• Avoiding contamination of freshwater sources

Fasciolopsis vs. Fasciola

Fasciolopsis buski

→ Intestinal fluke

→ Adult worms live in the small intestine

→ Causes fasciolopsiasis

→ Diarrhea, vomiting, anorexia, and possible intestinal obstruction

→ Praziquantel is the classic treatment

Fasciola hepatica / F. gigantica

→ Liver flukes

→ Primarily involve the liver and biliary tree

→ Cause fascioliasis

→ Hepatic migration may produce RUQ pain and eosinophilia

→ Triclabendazole is the key treatment

High-Yield Clinical Pattern

Patient from rural Southeast or South Asia

• ●

Consumption of contaminated aquatic vegetation

• ●

Diarrhea, vomiting, anorexia, or abdominal symptoms

• ●

Large intestinal trematode eggs in stool

→ Think Fasciolopsis buski

Severe Infection Pattern

Heavy intestinal fluke burden

• ●

Acute abdominal symptoms

• ●

Mechanical intestinal obstruction

→ Consider severe Fasciolopsis buski infection

Exam Essentials

Organism: Fasciolopsis buski

Type: Trematode helminth

Common name: Large intestinal fluke

Adult size: Approximately 7 cm

Distribution: Rural Southeast Asia and South Asia

Primary site: Small intestine

Transmission: Ingestion of metacercariae on aquatic vegetation

Intermediate host: Freshwater snail

Disease: Fasciolopsiasis

Major symptoms: Diarrhea, constipation, vomiting, anorexia

Major rare complication: Acute intestinal obstruction

Diagnosis: Parasitologic stool examination

Treatment: Praziquantel 25 mg/kg every 8 hours for 1 day

Alternative in source: Niclosamide

Key clinical pearl: Fasciolopsis buski is a large intestinal fluke acquired from contaminated aquatic vegetation; remember small-intestinal disease + gastrointestinal symptoms + possible obstruction, in contrast to Fasciola species, which primarily cause hepatic and biliary disease.

Infectious Disease and Microbiology – Fasciola Species

Overview

Fasciola species are trematode helminths (liver flukes) that cause fascioliasis, a parasitic infection primarily involving the liver and biliary tract.

The two major species are Fasciola hepatica and Fasciola gigantica. Humans are accidental hosts, while the normal definitive hosts include sheep, cattle, and other herbivorous animals.

⸻

Important Species

The principal human pathogens are:

• Fasciola hepatica

• Fasciola gigantica

F. hepatica is commonly known as the common liver fluke, whereas F. gigantica is generally larger and occurs predominantly in tropical regions.

⸻

Microbiologic Characteristics

Fasciola species are:

• Trematodes (flukes)

• Helminthic parasites

• Leaf-shaped adult worms

• Approximately several centimeters in length

Adult Fasciola organisms inhabit the biliary system of their definitive hosts.

⸻

Epidemiology

Fascioliasis occurs worldwide, although human infection is relatively uncommon.

The parasites naturally infect:

• Sheep

• Cattle

• Other grazing herbivores

Human disease is particularly associated with sheep- and cattle-raising regions where the parasite’s life cycle is maintained.

⸻

Humans as Accidental Hosts

Humans are accidental definitive hosts.

Human infection occurs when infective metacercariae are ingested, classically on contaminated aquatic vegetation.

Ingestion → intestinal penetration → hepatic migration → biliary tract maturation

⸻

Transmission

A classic source of human infection is consumption of raw aquatic plants, particularly watercress, contaminated with metacercariae.

Contaminated water can also serve as a source.

Freshwater snails participate as intermediate hosts in the parasite’s life cycle.

⸻

Fascioliasis

The disease caused by Fasciola species is:

Fascioliasis

It primarily involves the:

Liver

and

Biliary tree

Disease can be divided conceptually into an early hepatic migratory phase and a later biliary phase.

⸻

Acute Hepatic Phase

After ingestion, immature flukes penetrate the intestinal wall and migrate through the peritoneal cavity into the liver.

Migration through hepatic tissue may produce:

• Fever

• Right upper-quadrant abdominal pain

• Hepatomegaly

• Malaise

• Nausea

• Urticaria or other allergic manifestations

• Peripheral eosinophilia

This phase reflects tissue migration rather than established adult worms in the bile ducts.

⸻

Chronic Biliary Phase

After reaching maturity, adult flukes enter the biliary ducts.

Chronic infection may produce:

• Biliary inflammation

• Recurrent right upper-quadrant pain

• Cholangitis

• Biliary obstruction

• Jaundice

Some infections remain relatively asymptomatic.

⸻

Obstructive Cholangitis

Adult flukes may occasionally produce mechanical obstruction of the biliary tract, resulting in obstructive cholangitis.

In this situation, endoscopic intervention may be necessary in addition to antiparasitic treatment.

⸻

Ectopic Fascioliasis

Rarely, Fasciola parasites migrate outside their usual hepatic and biliary locations.

Such ectopic infection has been described particularly with F. gigantica.

Clinical manifestations depend on the organ involved.

⸻

Diagnosis

Diagnosis shares some features with other hepatobiliary fluke infections such as Clonorchis sinensis.

Methods include:

• Parasitologic examination for characteristic eggs

• Serologic testing

• Molecular testing such as PCR for species identification

⸻

Stool Examination

Characteristic Fasciola eggs may be detected in stool once adult parasites have matured in the biliary tract and begun producing eggs.

However, during the early hepatic migratory phase, stool examination may be negative because immature parasites have not yet begun producing eggs.

⸻

Serology

Serologic testing is particularly useful during early infection when clinical manifestations and eosinophilia are present but eggs are not yet detectable in stool.

Thus:

Acute hepatic symptoms + eosinophilia + exposure history + negative stool examination

→ Consider Fasciola serology

⸻

PCR

PCR-based testing can assist with detection and differentiation of Fasciola species where available.

⸻

Treatment

The source reflects older therapeutic information and states that satisfactory antiparasitic treatment was limited.

It describes:

Bithionol 30–50 mg/kg on alternate days for 10–14 doses

as having moderate effectiveness.

⸻

Triclabendazole

The source describes triclabendazole 10 mg/kg as a single dose as a veterinary product that had occasionally been used in humans and was not FDA-approved at the time the source was written.

Importantly, that information is now historically outdated: triclabendazole subsequently became an approved human treatment for fascioliasis in the United States.

It is the key drug associated with treatment of Fasciola infection.

⸻

Praziquantel

The source lists:

Praziquantel

as additional therapy.

However, a major high-yield distinction is that Fasciola species respond poorly to praziquantel, unlike several other trematode infections.

Therefore, the classic treatment association to remember is:

Fascioliasis → triclabendazole

⸻

Endoscopic Treatment

When adult flukes produce significant biliary obstruction or obstructive cholangitis, ERCP (endoscopic retrograde cholangiopancreatography) can be used to identify and remove parasites from the biliary tract.

Thus, severe mechanical obstruction may require:

Antiparasitic treatment + endoscopic source control

⸻

High-Yield Clinical Pattern

Sheep/cattle-raising region

Raw aquatic vegetation or watercress exposure

Right upper-quadrant pain and hepatomegaly

Marked eosinophilia

→ Think Fasciola hepatica or Fasciola gigantica

⸻

Chronic Disease Pattern

Biliary colic or cholangitis

Adult liver fluke in the biliary tree

Characteristic eggs in stool

→ Think chronic fascioliasis

⸻

Fasciola vs. Clonorchis

Fasciola

→ Infection classically from aquatic vegetation/watercress

→ Migrates through liver parenchyma

→ Acute phase commonly associated with eosinophilia

→ Treatment classically associated with triclabendazole

Clonorchis sinensis

→ Infection from raw or undercooked freshwater fish

→ Primarily inhabits the biliary ducts

→ Chronic infection associated with cholangiocarcinoma

→ Typically treated with praziquantel

⸻

Exam Essentials

Genus: Fasciola

Species: F. hepatica, F. gigantica

Type: Trematode/liver fluke

Natural hosts: Sheep, cattle, and other herbivores

Human role: Accidental host

Intermediate host: Freshwater snail

Classic exposure: Raw aquatic vegetation, especially watercress

Primary organs: Liver and biliary tree

Acute phase: Hepatic migration

Important laboratory clue: Eosinophilia

Chronic phase: Biliary disease

Diagnosis: Stool examination, serology, and molecular methods where available

Early infection: Stool may be negative

Key treatment association: Triclabendazole

Praziquantel: Poor activity against Fasciola

Biliary obstruction: May require ERCP and parasite removal

⸻

Key clinical pearl: Think Fasciola when a patient with raw watercress/aquatic-plant exposure develops right upper-quadrant pain, hepatomegaly, and eosinophilia. Unlike many other trematodes, the key treatment is triclabendazole rather than praziquantel.

Infectious Disease and Microbiology – Exophiala Species

Overview

Exophiala species are dematiaceous (darkly pigmented) filamentous fungi that are distributed worldwide. They are uncommon causes of human disease but can produce cutaneous, subcutaneous, ocular, pulmonary, and invasive systemic infections.

Because of their melanin-containing cell walls and pigmented hyphae, infections caused by these organisms are generally classified among the phaeohyphomycoses.

Important Species

Clinically recognized species include:

• Exophiala dermatitidis

• Exophiala jeanselmei

• Exophiala moniliae

• Exophiala pisciphila

• Exophiala spinifera

Different species vary in their clinical associations and potential for invasive disease.

Microbiologic Characteristics

Exophiala species are:

• Dematiaceous fungi

• Filamentous molds

• Characterized by dark pigmentation related to melanin in the fungal cell wall

In infected tissue, they may appear as:

• Yeast-like forms

• Pseudohyphae

• Septate pigmented hyphae

Dematiaceous Fungi

The term dematiaceous refers to fungi with brown-to-black pigmentation in their cell walls.

When these pigmented fungi produce infection characterized by yeast-like cells, pseudohyphae, or irregular pigmented hyphae in tissue, the disease is generally termed:

Phaeohyphomycosis

Epidemiology

Exophiala species have a worldwide distribution.

Despite their environmental distribution, human infections are rare.

Disease may remain localized or, particularly in susceptible hosts, become invasive.

Clinical Infections

Reported infections include:

• Corneal infection

• Cutaneous and subcutaneous infection

• Prosthetic valve endocarditis

• Septic arthritis

• Brain abscess

• Pneumonia

• Other systemic infections

The clinical spectrum therefore ranges from localized superficial disease to potentially severe invasive infection.

Corneal Infection

Exophiala species can occasionally cause fungal keratitis.

Clinical manifestations may include:

• Eye pain

• Redness

• Photophobia

• Decreased vision

• Corneal inflammation or ulceration

A history of ocular trauma or environmental exposure may provide a clue to fungal infection.

Subcutaneous Infection

One of the better-recognized manifestations is subcutaneous phaeohyphomycosis.

Patients may develop:

• Slowly enlarging nodules

• Cysts

• Abscess-like lesions

• Chronic localized swelling

Traumatic implantation of environmental fungal material into the skin or subcutaneous tissue may initiate infection.

Pneumonia

Pulmonary infection due to Exophiala species is uncommon but has been reported.

Manifestations can range from chronic respiratory infection to invasive pneumonia, depending on the species and host factors.

Prosthetic Valve Endocarditis

Rare cases of Exophiala-associated prosthetic valve endocarditis have been reported.

This represents a serious invasive infection and may be difficult to eradicate because both fungal infection and infected prosthetic material are involved.

Septic Arthritis

Exophiala species have occasionally been associated with fungal arthritis.

Diagnosis generally requires demonstration of the fungus in synovial fluid or tissue together with compatible clinical findings.

Brain Abscess

One of the most serious manifestations is cerebral infection with brain abscess formation.

Certain dematiaceous fungi have a notable ability to cause central nervous system disease.

Neurologic manifestations may include:

• Headache

• Altered mental status

• Focal neurologic deficits

• Seizures

Systemic Infection

Although uncommon, disseminated or systemic Exophiala infection can occur and may involve multiple organs.

Invasive disease is potentially life-threatening and requires accurate species identification and antifungal management.

Diagnosis

Diagnosis is based on:

Culture of the fungus

and

Histopathologic examination of infected tissue

Using both methods can help establish that the recovered fungus represents true tissue infection.

Histopathology

Histopathologic examination may demonstrate:

Pigmented yeast-like cells

• ●

Pseudohyphae

• ●

Septate, darkly pigmented hyphae

These findings are characteristic of phaeohyphomycosis caused by dematiaceous fungi.

Culture

Fungal culture allows isolation and identification of Exophiala species.

Because treatment response may vary between species and isolates, accurate identification and, in severe disease, consideration of antifungal susceptibility information can be valuable.

Treatment

The source describes treatment with:

Amphotericin B

with or without:

Flucytosine

The optimal treatment depends on the site and severity of infection.

Additional Treatment

The source also lists:

Itraconazole

as an alternative antifungal agent.

Localized disease and invasive systemic infection may require substantially different therapeutic approaches.

Surgical Management

For localized subcutaneous lesions, abscesses, infected prosthetic material, or cerebral lesions, surgical management may sometimes be required in addition to antifungal therapy.

Management of invasive disease should therefore consider both antifungal treatment and appropriate source control.

High-Yield Clinical Pattern

Chronic subcutaneous cyst or nodule

• ●

Dematiaceous fungus

• ●

Pigmented septate hyphae in tissue

→ Think phaeohyphomycosis due to Exophiala species

Invasive Disease Pattern

Pigmented fungus

• ●

Pneumonia, prosthetic valve endocarditis, arthritis, or brain abscess

→ Consider invasive Exophiala infection

Exam Essentials

Genus: Exophiala

Type: Dematiaceous filamentous fungus

Pigment: Melanin-containing/dark fungal elements

Tissue morphology: Yeasts, pseudohyphae, and septate pigmented hyphae

Distribution: Worldwide

Frequency: Rare human pathogen

Disease category: Phaeohyphomycosis

Localized infections: Corneal and subcutaneous disease

Invasive infections: Pneumonia, arthritis, endocarditis, brain abscess

Diagnosis: Fungal culture + histopathology

Treatment in source: Amphotericin B ± flucytosine

Additional treatment: Itraconazole

Management consideration: Surgical intervention/source control may be necessary for selected localized or invasive lesions

Key clinical pearl: Exophiala species are dematiaceous fungi causing phaeohyphomycosis, recognized by pigmented septate hyphae, yeast-like forms, or pseudohyphae in tissue; although infection is usually rare and localized, these organisms can occasionally produce severe disease such as prosthetic valve endocarditis, pneumonia, and brain abscess.

Infectious Disease and Microbiology – Ewingella americana

Overview

Ewingella americana is a rare aerobic Gram-negative bacillus historically classified within the Enterobacteriaceae. It is infrequently recovered from clinical specimens, and because of its rarity, its overall clinical significance and pathogenic potential remain incompletely defined.

Reported infections have occurred particularly in immunocompromised patients and include bacteremia, wound infections, and occasional respiratory tract infections.

Microbiologic Characteristics

Ewingella americana is:

• An aerobic Gram-negative bacillus

• Historically classified within the Enterobacteriaceae group

• A rare opportunistic human pathogen

Its uncommon isolation makes it difficult to establish its precise role in many clinical settings.

Epidemiology

E. americana is rarely recovered in clinical cultures.

Consequently, considerably less is known about its epidemiology than about more common Gram-negative pathogens.

Clinical Significance

The clinical significance of E. americana can sometimes be uncertain, particularly when it is recovered from specimens that may contain colonizing organisms.

However, documented invasive infections indicate that it can function as an opportunistic pathogen, especially in susceptible hosts.

Risk Factors

Reported infections are particularly relevant in patients with:

• Immunocompromising conditions

• Significant underlying disease

• Wounds or disrupted tissue barriers

• Healthcare exposure

Because relatively few cases have been reported, the complete spectrum of risk factors remains uncertain.

Bacteremia

E. americana has been reported as a cause of bacteremia, particularly in immunocompromised patients.

Isolation from blood should therefore be evaluated carefully in conjunction with the patient’s clinical condition rather than automatically dismissed because the organism is uncommon.

Wound Infection

The organism has also been associated with wound infections, particularly in patients with impaired host defenses.

Clinical significance is more convincing when the organism is recovered from an infected wound together with compatible inflammatory findings.

Respiratory Tract Infection

E. americana has rarely been associated with respiratory tract infection.

Because respiratory specimens can contain colonizing organisms, recovery from the respiratory tract should be interpreted together with clinical and radiologic evidence of infection.

Diagnosis

Diagnosis is established by:

Culture of the organism

Because E. americana is unusual, accurate laboratory identification is important.

For clinically significant isolates, antimicrobial susceptibility testing is particularly valuable because predictable susceptibility patterns cannot always be assumed.

Treatment

There are limited clinical data regarding optimal antimicrobial therapy for E. americana infection.

The source reports activity with agents including:

• Cefotaxime

• Piperacillin–tazobactam

• Trimethoprim–sulfamethoxazole

However, antimicrobial susceptibility should ideally be determined for the individual isolate.

Multidrug Resistance

An important concern is that multidrug-resistant isolates have been reported.

Therefore:

Rare organism + uncertain susceptibility + possible multidrug resistance

→ Culture and susceptibility-guided therapy are particularly important

Combination Therapy

The source describes clinical use of combinations involving:

Trimethoprim–sulfamethoxazole

or

Cefotaxime

or

An antipseudomonal penicillin

combined with an:

Aminoglycoside

Because evidence is limited, these historical treatment approaches should not be considered universally appropriate for every isolate.

Treatment Principle

The most important therapeutic concept is:

Identify the organism

• ●

Perform antimicrobial susceptibility testing

• ●

Choose therapy according to susceptibility and infection severity

This is especially important because E. americana is uncommon and antimicrobial resistance has been reported.

High-Yield Clinical Pattern

Immunocompromised patient

• ●

Bacteremia or wound infection

• ●

Unusual aerobic Gram-negative bacillus

• ●

Potential multidrug resistance

→ Consider Ewingella americana

Exam Essentials

Organism: Ewingella americana

Type: Gram-negative bacillus

Oxygen requirement: Aerobic

Traditional classification: Enterobacteriaceae

Frequency: Very rare

Clinical significance: Incompletely defined

Important host: Immunocompromised patient

Major reported infections: Bacteremia and wound infection

Respiratory infection: Rare

Diagnosis: Culture

Important laboratory step: Antimicrobial susceptibility testing

Resistance: Multidrug resistance has been reported

Reported active agents in source: Cefotaxime, piperacillin–tazobactam, trimethoprim–sulfamethoxazole

Treatment principle: Susceptibility-guided therapy

Key clinical pearl: Ewingella americana is a rare opportunistic Gram-negative bacillus associated mainly with bacteremia and wound infection in immunocompromised patients; because clinical experience is limited and multidrug resistance can occur, antimicrobial susceptibility testing is central to treatment selection.

Infectious Disease and Microbiology – Eubacterium Species

Overview

Eubacterium species are anaerobic, pleomorphic Gram-positive bacilli that form part of the normal human microbiota. Because these organisms normally colonize the body, their recovery from a clinical specimen does not automatically establish that they are causing infection.

When pathogenic, Eubacterium species are commonly associated with polymicrobial infections, particularly abscesses, periodontal disease, and infections arising from sites containing anaerobic flora.

Important Species

Species described in this group include:

• Eubacterium lentum

• Eubacterium nodatum

• Eubacterium timidum

• Other Eubacterium species

Some organisms historically classified as Eubacterium have undergone taxonomic reclassification, so older names may still appear in infectious-disease literature.

Microbiologic Characteristics

Eubacterium species are:

• Anaerobic

• Gram-positive bacilli

• Pleomorphic in appearance

• Components of normal human flora

Their anaerobic nature means that specimens must be collected and transported appropriately if culture is required.

Epidemiology

Eubacterium species are members of the normal human microbiota.

They may inhabit sites such as the gastrointestinal tract and oral cavity.

Because colonization is common, isolation of an organism must always be interpreted in the context of the patient’s clinical syndrome and the specimen source.

Colonization vs. Infection

A particularly important principle is:

Positive culture ≠ necessarily active infection

Isolation from a normally colonized site may simply represent normal flora or contamination.

Evidence for true infection is stronger when the organism is recovered from a normally sterile site, particularly when accompanied by compatible clinical findings.

Clinical Infections

When Eubacterium species cause disease, infections may include:

• Abscesses

• Periodontal infections

• Septic arthritis

• Gynecologic infections such as endometritis

• Other anaerobic infections

These infections are almost always polymicrobial, meaning other bacterial species are frequently present.

Abscesses and Mixed Infections

Eubacterium species may be recovered from abscesses and infections at various anatomical sites.

A typical pattern is:

Disruption of mucosal barrier

→

Normal anaerobic flora enters deeper tissue

→

Polymicrobial abscess or invasive infection

This is characteristic of many infections caused by endogenous anaerobic flora.

Periodontal Disease

Certain Eubacterium species have been associated with periodontal disease.

The oral cavity contains a complex anaerobic microbiome, so periodontal infections are usually polymicrobial rather than caused by a single organism.

Eubacterium lentum

The source associates Eubacterium lentum with:

Septic arthritis in patients with colonic lesions

This association suggests that disruption of the gastrointestinal mucosal barrier may permit organisms from intestinal flora to enter the bloodstream and subsequently involve a joint.

Eubacterium nodatum

The source associates Eubacterium nodatum with:

Endometritis in women using an intrauterine device (IUD)

This represents another example of an anaerobic organism associated with infection following alteration or disruption of normal mucosal environments.

Diagnosis

Diagnosis is established by:

Culture using appropriate anaerobic media

Successful isolation requires appropriate specimen collection and maintenance of anaerobic conditions during transport and processing.

Interpretation of Culture

Because Eubacterium species are normal flora, laboratory isolation should be interpreted together with:

• Clinical manifestations

• Anatomical source of the specimen

• Presence of abscess or tissue inflammation

• Recovery from a normally sterile site

• Presence of additional organisms

The organism’s presence alone does not prove causation.

Treatment

The source lists:

Penicillin G

or

A cephamycin

as treatment options.

It also lists:

Metronidazole

for anaerobic coverage.

Additional Treatment

Other antimicrobial agents described in the source include:

• Imipenem

• Meropenem

• Clindamycin

• Ureidopenicillins

For clinically significant infection, antimicrobial selection should take into account the susceptibility pattern and other organisms present in a polymicrobial infection.

Source Control

Because these organisms frequently occur in abscesses and mixed anaerobic infections, antimicrobial therapy may need to be combined with appropriate source control.

This can include drainage of an abscess, debridement of infected tissue, or management of an underlying anatomical source.

High-Yield Clinical Pattern

Anaerobic Gram-positive bacillus

• ●

Normally part of human flora

• ●

Recovered from an abscess or other polymicrobial infection

→ Think Eubacterium species

Important Interpretation Pattern

Eubacterium isolated from a colonized site

→ May represent normal flora

Eubacterium isolated from a sterile site + compatible infection

→ More supportive of true invasive infection

Exam Essentials

Genus: Eubacterium

Type: Pleomorphic Gram-positive bacillus

Oxygen requirement: Anaerobic

Normal habitat: Part of normal human flora

Major infection pattern: Polymicrobial anaerobic infection

Common manifestations: Abscesses and periodontal disease

E. lentum: Associated in the source with septic arthritis in patients with colonic lesions

E. nodatum: Associated in the source with endometritis in women using an IUD

Diagnosis: Anaerobic culture

Important diagnostic issue: Isolation does not necessarily indicate infection

Treatment in source: Penicillin G, cephamycins, or metronidazole

Additional agents: Carbapenems, clindamycin, or ureidopenicillins

Management principle: Consider source control for abscesses

Key clinical pearl: Because Eubacterium species are part of the normal human flora, a positive culture does not by itself establish disease; true infections are typically anaerobic, polymicrobial infections, especially abscesses and infections arising after disruption of normal mucosal barriers.

Infectious Disease and Microbiology – Erysipelothrix rhusiopathiae

Overview

Erysipelothrix rhusiopathiae is a Gram-positive bacillus that causes a characteristic occupational skin infection known as erysipeloid. Human infection is uncommon but occurs worldwide and is strongly associated with exposure to fish, shellfish, animals, animal products, or contaminated soil.

Although most infections remain localized to the skin, the organism can occasionally cause diffuse cutaneous disease, bacteremia, and infective endocarditis.

Microbiologic Characteristics

Erysipelothrix rhusiopathiae is an:

• Aerobic Gram-positive bacillus

• Zoonotic pathogen

• Environmental and animal-associated organism

It is especially notable for causing infection after inoculation through minor skin trauma during occupational exposure.

Incubation Period

The incubation period is:

Not clearly defined

Clinical infection usually follows direct inoculation of the organism into damaged skin.

Epidemiology

Human infection is rare but occurs worldwide.

Exposure is classically associated with people who handle:

• Fish

• Crustaceans and shellfish

• Meat or animal carcasses

• Livestock

• Animal products

• Soil contaminated by animals

Occupational risk is therefore increased in fish handlers, butchers, veterinarians, farmers, and similar workers.

Erysipeloid

The classic localized infection caused by E. rhusiopathiae is called:

Erysipeloid

This is a localized cutaneous infection that usually develops at the site of inoculation.

Clinical Features of Erysipeloid

Typical findings include:

• Painful or burning skin lesion

• Erythematous to violaceous discoloration

• Well-demarcated margins

• Gradual peripheral expansion

• Common involvement of the hands or fingers

Systemic symptoms are usually absent or mild in localized disease.

Diffuse Cutaneous Disease

Some patients may develop a more widespread cutaneous eruption accompanied by systemic symptoms.

Possible manifestations include:

• Fever

• Myalgias

• Arthralgias

• Multiple skin lesions

This represents a more extensive form of infection than classic localized erysipeloid.

Bacteremia

Rarely, E. rhusiopathiae can invade the bloodstream and cause:

Bacteremia

Bloodstream infection should raise concern for deeper or systemic involvement.

Infective Endocarditis

One of the most important severe manifestations is:

Infective endocarditis

Historically, E. rhusiopathiae bacteremia has had a notable association with endocarditis.

Patients with systemic infection may therefore require evaluation for cardiac involvement when clinically appropriate.

Diagnosis

Diagnosis is established by:

Culture of the organism

Specimens depend on the clinical syndrome and may include tissue or blood.

Because localized lesions can have relatively few organisms, obtaining an appropriate deeper specimen may improve diagnostic yield.

Treatment

The source recommends:

Penicillin G for 10 days

Penicillin has traditionally been considered an effective treatment for susceptible E. rhusiopathiae infection.

Additional Treatment Options

Alternative agents listed in the source include:

• Cephalosporins

• Clindamycin

• Ciprofloxacin

• Carbapenems such as imipenem or meropenem

Choice of therapy should depend on disease severity and susceptibility when available.

Important Antibiotic Pearl

A useful microbiology distinction is that Erysipelothrix rhusiopathiae is characteristically resistant to vancomycin.

This is clinically important because vancomycin is often used empirically for Gram-positive infections, but it is not a reliable treatment for this organism.

Occupational Exposure Pattern

A classic exposure history is:

Fish or animal handler

• ●

Minor cut or puncture wound

• ●

Painful violaceous hand lesion

→ Think Erysipelothrix rhusiopathiae

Differential Diagnosis

Localized erysipeloid may resemble:

• Cellulitis

• Erysipelas

• Contact dermatitis

• Other occupational skin infections

The exposure history is often the major clue.

High-Yield Clinical Pattern

Handling fish, shellfish, meat, or animals

• ●

Localized painful violaceous skin lesion on the hand

• ●

Gram-positive bacillus

→ Think Erysipelothrix rhusiopathiae

Severe Disease Pattern

Systemic symptoms or bacteremia

• ●

Possible cardiac murmur or persistent bloodstream infection

→ Evaluate for infective endocarditis

Exam Essentials

Organism: Erysipelothrix rhusiopathiae

Type: Gram-positive bacillus

Distribution: Worldwide

Frequency: Rare

Classic disease: Erysipeloid

Typical exposure: Fish, crustaceans, animals, meat, or soil

Common site: Hands and fingers after occupational inoculation

Systemic manifestations: Fever, myalgias, arthralgias

Serious complications: Bacteremia and endocarditis

Diagnosis: Culture

Traditional treatment: Penicillin G

Alternative agents: Cephalosporins, clindamycin, ciprofloxacin, carbapenems

Important resistance clue: Vancomycin resistance

Key clinical pearl: Erysipelothrix rhusiopathiae should be suspected in a fish or animal handler with a painful violaceous hand lesion, and severe bacteremic disease is particularly important because of its association with infective endocarditis.

Infectious Disease and Microbiology – Enterovirus Group

Overview

Enteroviruses are a major group of small, single-stranded RNA viruses within the family Picornaviridae. They have a worldwide distribution and commonly infect humans.

The enterovirus group includes polioviruses, coxsackieviruses, echoviruses, and several numbered enteroviruses. Different members can cause illnesses ranging from mild febrile disease to conjunctivitis, meningitis, encephalitis, myocarditis, hand-foot-and-mouth disease, and poliomyelitis-like neurologic syndromes.

Picornaviridae

Two major groups of Picornaviridae commonly associated with human disease are:

• Enteroviruses

• Rhinoviruses

Both are small RNA viruses, but their tissue tropism and clinical manifestations differ considerably.

Enterovirus Subgroups

Traditionally, the enterovirus group includes:

• Polioviruses – serotypes 1–3

• Coxsackievirus A – multiple serotypes

• Coxsackievirus B – multiple serotypes

• Echoviruses

• Numbered enteroviruses, including EV-A71 and EV-D68

Older classifications sometimes referred to hepatitis A virus as enterovirus 72, but hepatitis A virus is now classified in the genus Hepatovirus within Picornaviridae rather than as an enterovirus.

Microbiologic Characteristics

Enteroviruses are:

• Single-stranded RNA viruses

• Positive-sense RNA viruses

• Nonenveloped (naked)

• Icosahedral

Their lack of an envelope contributes to their ability to remain relatively stable in the environment.

Epidemiology

Enterovirus infections are common worldwide.

Transmission frequently occurs through the fecal–oral route, although some enteroviruses can also spread through respiratory secretions or direct contact with contaminated material.

Incubation Period

The incubation period varies considerably depending on the specific enterovirus and clinical syndrome.

For acute hemorrhagic conjunctivitis, the source describes a particularly short incubation period of:

12–72 hours

This short incubation can contribute to rapid spread during outbreaks.

Clinical Spectrum

Enteroviruses can cause a remarkably broad range of diseases, including:

• Febrile illness

• Skin and mucosal eruptions

• Hand-foot-and-mouth disease

• Herpangina

• Acute hemorrhagic conjunctivitis

• Aseptic meningitis

• Encephalitis

• Myocarditis and pericarditis

• Pleurodynia

• Poliomyelitis and poliomyelitis-like syndromes

• Severe neonatal infection

The clinical syndrome varies according to the specific virus and host.

Acute Hemorrhagic Conjunctivitis

Enterovirus 70 (EV-70) is classically associated with acute hemorrhagic conjunctivitis.

The illness has a rapid onset and can spread efficiently between individuals.

Clinical Features of Acute Hemorrhagic Conjunctivitis

Typical manifestations include:

• Acute eye pain or irritation

• Conjunctival redness

• Eyelid swelling

• Excessive tearing

• Foreign-body sensation

• Subconjunctival hemorrhage

The hemorrhagic appearance is a characteristic feature.

Enterovirus A71

Enterovirus A71 (EV-A71) is an important neurotropic enterovirus.

It can cause:

• Hand-foot-and-mouth disease

• Skin rash

• Meningitis

• Encephalitis

• Brainstem encephalitis

• Acute flaccid paralysis or a poliomyelitis-like syndrome

Young children can develop particularly severe neurologic disease.

Poliomyelitis-Like Syndrome

Some non-polio enteroviruses can affect motor neurons and produce acute flaccid weakness or paralysis resembling poliomyelitis.

Thus:

Acute flaccid paralysis does not automatically mean poliovirus infection.

Other enteroviruses should also be considered.

Meningitis and Encephalitis

Enteroviruses are important causes of aseptic meningitis.

Neurologic manifestations may include:

• Fever

• Headache

• Neck stiffness

• Photophobia

• Vomiting

When brain tissue is involved, patients may develop encephalitis, characterized by altered mental status, seizures, or other neurologic abnormalities.

Diagnosis

Traditional diagnostic methods include:

• Cell culture

• Serologic testing

Serology may provide supportive evidence in selected clinical situations.

Molecular Diagnosis

In modern clinical practice, RT-PCR and other nucleic-acid amplification tests are important methods for detecting enterovirus RNA.

Depending on the syndrome, testing may be performed on:

• Cerebrospinal fluid

• Respiratory specimens

• Stool

• Blood

• Vesicular or other lesion specimens

For suspected enteroviral meningitis, molecular detection from CSF can be particularly useful.

Treatment

Treatment is primarily:

Symptomatic and supportive

Management depends on the clinical syndrome and severity of infection.

Antiviral Therapy

The source states:

There is no effective specific antiviral treatment routinely available.

Supportive management may include hydration, analgesia, fever control, neurologic monitoring, and intensive care when severe CNS or cardiopulmonary complications occur.

Prevention

Good hygiene is important because enteroviruses can spread through contaminated hands, surfaces, respiratory secretions, and fecal material.

Preventive measures include:

• Frequent handwashing

• Appropriate sanitation

• Cleaning contaminated surfaces

• Avoiding close contact during contagious illness

• Avoiding sharing personal items

Conjunctivitis Prevention

During outbreaks of acute hemorrhagic conjunctivitis:

Do not share towels or other personal items that contact the eyes or face.

This helps prevent indirect transmission of the virus between individuals.

High-Yield Clinical Pattern – Enterovirus 70

Very short incubation of 12–72 hours

• ●

Rapid-onset conjunctivitis

• ●

Subconjunctival hemorrhage

→ Think Enterovirus 70

High-Yield Clinical Pattern – Enterovirus A71

Young child

• ●

Hand-foot-and-mouth disease or rash

• ●

Encephalitis or acute flaccid paralysis

→ Think Enterovirus A71

Exam Essentials

Group: Enterovirus

Family: Picornaviridae

Genome: Positive-sense single-stranded RNA

Envelope: Absent (naked)

Capsid: Icosahedral

Distribution: Worldwide

Frequency: Common

Major transmission: Fecal–oral; some also spread through respiratory/contact routes

EV-70: Acute hemorrhagic conjunctivitis

EV-70 incubation: 12–72 hours

EV-A71: Hand-foot-and-mouth disease + neurologic disease

Neurologic manifestations: Meningitis, encephalitis, acute flaccid paralysis

Diagnosis: Molecular testing, with culture and serology in selected settings

Treatment: Supportive

Specific routine antiviral treatment: None

Conjunctivitis prevention: Avoid sharing towels and other potentially contaminated personal items

Historical terminology: Hepatitis A was formerly called enterovirus 72 but is now classified as a Hepatovirus

Key clinical pearl: Remember EV-70 → acute hemorrhagic conjunctivitis, while EV-A71 → hand-foot-and-mouth disease with potential severe neurologic complications such as encephalitis and poliomyelitis-like acute flaccid paralysis.

Infectious Disease and Microbiology – Enterococcus Species

Overview

Enterococcus species are Gram-positive cocci that normally colonize the human gastrointestinal tract but are important causes of healthcare-associated and opportunistic infections. The most clinically important species are Enterococcus faecalis and Enterococcus faecium.

Major infections include urinary tract infection, bacteremia, endocarditis, intra-abdominal and pelvic infection, neonatal infection, meningitis, and skin and soft-tissue infection.

Important Species

Clinically recognized species include:

• Enterococcus faecalis

• Enterococcus faecium

• Enterococcus avium

• Enterococcus casseliflavus

• Enterococcus durans

• Enterococcus gallinarum

• Enterococcus hirae

• Other Enterococcus species

Among these, E. faecalis and E. faecium account for most clinically important infections.

Microbiologic Characteristics

Enterococcus species are:

• Gram-positive cocci

• Facultatively anaerobic organisms

• Normal inhabitants of the gastrointestinal tract

• Opportunistic pathogens

• Notable for substantial intrinsic and acquired antimicrobial resistance

They were historically classified among the group D streptococci.

Colonization and Incubation

A conventional incubation period is difficult to define.

Infection commonly develops after a prolonged period of intestinal colonization, particularly in hospitalized or medically complex patients.

The sequence is often:

Intestinal colonization → disruption of host barriers or medical intervention → invasion → clinical infection

Epidemiology

Enterococcus species have become increasingly important causes of healthcare-associated infection.

They are prominent causes of hospital-acquired bacteremia, urinary tract infection, and infections involving indwelling medical devices.

Risk Factors

Important risk factors for invasive enterococcal infection include:

• Prolonged hospitalization

• Broad-spectrum antibiotic exposure

• Urinary or vascular catheters

• Recent surgery

• Intra-abdominal disease

• Immunosuppression

• Severe underlying illness

Bacteremia

Enterococcus species are important causes of bloodstream infection.

Bacteremia may be either:

• Monomicrobial

• Polymicrobial, particularly when arising from gastrointestinal or intra-abdominal sources

Potential sources include urinary infection, intra-abdominal infection, vascular catheters, and endocarditis.

Urinary Tract Infection

Enterococci are important causes of urinary tract infection, especially in hospitalized patients.

Risk is increased by:

• Indwelling urinary catheters

• Urinary instrumentation

• Structural urinary tract disease

• Prolonged hospitalization

Clinical disease ranges from cystitis to complicated UTI and urosepsis.

Infective Endocarditis

Enterococci can cause acute or subacute infective endocarditis.

E. faecalis is particularly important in this setting.

Patients may develop:

• Persistent bacteremia

• Fever

• Cardiac murmur

• Valvular vegetations

• Embolic or immunologic complications

Enterococcal endocarditis can be difficult to eradicate and generally requires prolonged antimicrobial therapy.

Intra-Abdominal and Pelvic Infection

Because enterococci normally colonize the gastrointestinal tract, they may participate in:

• Intra-abdominal abscesses

• Peritonitis

• Biliary infection

• Pelvic infections

• Postoperative abdominal infections

These infections are frequently polymicrobial.

Neonatal Infection

Enterococci can occasionally cause serious infections in neonates, particularly in hospitalized or premature infants.

Manifestations may include:

• Sepsis

• Bacteremia

• Meningitis

Meningitis

Enterococcal meningitis is uncommon but may occur in:

• Neonates

• Neurosurgical patients

• Immunocompromised individuals

• Patients with invasive enterococcal infection

Pneumonia

Enterococcus may occasionally be isolated in patients with pulmonary disease.

However, true enterococcal pneumonia is uncommon, and isolation from respiratory specimens should be interpreted carefully because colonization can occur.

Skin and Soft-Tissue Infection

Enterococci may participate in skin, soft-tissue, and wound infections, particularly in hospitalized patients.

These infections are frequently polymicrobial and may occur in surgical wounds or chronic ulcers.

Diagnosis

Diagnosis is established by culture of the pathogen from the appropriate clinical specimen.

Examples include:

• Blood cultures

• Urine culture

• Wound or abscess cultures

• Cerebrospinal fluid culture

Because antimicrobial resistance is common, susceptibility testing is essential for clinically significant infection.

Enterococcus faecalis Treatment

The source lists the following agents for susceptible E. faecalis:

• Amoxicillin

• Ampicillin

• Penicillin G

Ampicillin is commonly active against susceptible E. faecalis isolates.

Serious Infection and Endocarditis

The source describes treatment of serious infection or endocarditis using a cell-wall-active β-lactam combined with gentamicin, provided the organism does not demonstrate high-level aminoglycoside resistance.

The purpose of combination therapy is to achieve synergistic bactericidal activity.

Ampicillin + Gentamicin Synergy

The traditional principle is:

Ampicillin or penicillin damages the bacterial cell wall

• ●

Gentamicin enters the organism more effectively

→ Synergistic killing

However, high-level aminoglycoside resistance eliminates this synergistic effect.

Endocarditis Duration

Enterococcal endocarditis generally requires prolonged therapy.

The source describes:

Approximately 6 weeks of antimicrobial treatment

The exact regimen and duration depend on the valve involved, susceptibility pattern, prior therapy, and clinical circumstances.

Enterococcus faecium

E. faecium is particularly important because it is generally more antimicrobial-resistant than E. faecalis.

The source describes treatment with:

Vancomycin or teicoplanin, potentially combined with gentamicin when appropriate susceptibility is demonstrated.

However, resistant E. faecium strains are a major modern clinical problem.

Vancomycin-Resistant Enterococcus

A major high-yield concept is vancomycin-resistant Enterococcus (VRE).

VRE occurs particularly among E. faecium strains and is an important cause of healthcare-associated infection.

Resistance can substantially limit therapeutic options.

Important Intrinsic Vancomycin Resistance

E. gallinarum and E. casseliflavus have characteristic intrinsic low-level vancomycin resistance, associated with the VanC phenotype.

This distinguishes them from the acquired high-level vancomycin resistance encountered in many clinically important E. faecium isolates.

Additional Treatment Options

The source also lists:

• Imipenem

• Vancomycin

• Teicoplanin

• Amoxicillin–clavulanate

• Ampicillin–sulbactam

• Piperacillin–tazobactam

Actual therapy should be selected according to species identification, infection site, severity, and susceptibility testing.

Cystitis

For uncomplicated lower urinary infection, the source lists agents such as:

• Nitrofurantoin

• Ciprofloxacin

• Trimethoprim–sulfamethoxazole

However, susceptibility varies substantially, so urinary isolates should be interpreted according to the individual organism and susceptibility profile.

Important Resistance Characteristics

Enterococci are notable for resistance to many commonly used antimicrobial agents.

Important concepts include:

Intrinsic resistance to cephalosporins

Reduced susceptibility to many β-lactams

Possible high-level aminoglycoside resistance

Vancomycin resistance, especially in E. faecium

This combination of resistance mechanisms makes enterococci particularly important hospital pathogens.

E. faecalis vs. E. faecium

Enterococcus faecalis

→ More common in many clinical infections

→ Often more susceptible to ampicillin

→ Important cause of endocarditis and UTI

Enterococcus faecium

→ Generally more drug resistant

→ Frequently ampicillin resistant

→ Strongly associated with VRE

→ Particularly important in healthcare-associated infection

High-Yield Clinical Pattern

Hospitalized patient

• ●

Prolonged antibiotic exposure or indwelling catheter

• ●

UTI, bacteremia, or endocarditis

• ●

Gram-positive cocci with substantial antimicrobial resistance

→ Think Enterococcus

Endocarditis High-Yield Pattern

Persistent enterococcal bacteremia

• ●

Valvular vegetation/endocarditis

• ●

Need for prolonged therapy and bactericidal combination strategy when appropriate

→ Think Enterococcus faecalis

Exam Essentials

Genus: Enterococcus

Type: Gram-positive cocci

Normal habitat: Gastrointestinal tract

Major species: E. faecalis and E. faecium

Major infections: UTI, bacteremia, endocarditis, intra-abdominal and pelvic infection

Healthcare association: Strong

Diagnosis: Culture + susceptibility testing

E. faecalis: Often ampicillin susceptible

E. faecium: Generally more resistant

Important resistant phenotype: VRE, especially E. faecium

Aminoglycoside issue: High-level resistance eliminates synergistic killing

Endocarditis: Usually requires prolonged treatment

E. gallinarum/E. casseliflavus: Intrinsic VanC-mediated low-level vancomycin resistance

Cephalosporins: Enterococci are intrinsically resistant

Key clinical pearl: The major distinction is E. faecalis = often ampicillin susceptible and a classic cause of endocarditis, whereas E. faecium = substantially more drug resistant and strongly associated with VRE; serious enterococcal infections require susceptibility-guided therapy because intrinsic and acquired resistance are central features of this genus.

Infectious Disease and Microbiology – Enterobius vermicularis

Overview

Enterobius vermicularis is an intestinal nematode that causes enterobiasis, also called pinworm infection or oxyuriasis. It occurs worldwide and is particularly common in children and in households where reinfection can occur repeatedly.

The most characteristic symptom is perianal itching, especially at night.

⸻

Microbiologic Characteristics

Enterobius vermicularis is an intestinal nematode helminth.

Adult worms live mainly in the colon. At night, gravid female worms migrate to the perianal skin and deposit eggs, producing the characteristic itching associated with infection.

⸻

Life Cycle and Incubation

The life cycle of E. vermicularis is approximately:

2–6 weeks

However, repeated reinfection is common and may be necessary before symptoms become prominent.

⸻

Epidemiology

Pinworm infection has a worldwide distribution.

Transmission is especially common in:

• Children

• Families and household contacts

• Schools and daycare settings

• Crowded living environments

Because the eggs spread easily, infection can recur even after successful treatment.

⸻

Transmission

Transmission occurs mainly through the fecal–oral route after ingestion of infective eggs.

Eggs may contaminate:

• Hands and fingernails

• Bedding

• Clothing

• Toys

• Household surfaces

Autoinfection can occur when a person scratches the perianal area and later transfers eggs from the fingers to the mouth.

⸻

Enterobiasis

The disease caused by E. vermicularis is known as:

Enterobiasis

or

Pinworm infection

or

Oxyuriasis

Many infections are mild or asymptomatic.

⸻

Perianal Pruritus

The classic symptom is:

Nocturnal perianal itching

This occurs because female worms migrate out of the anus at night and deposit eggs on the surrounding skin.

Patients may develop:

• Intense itching

• Restless sleep

• Irritability

• Excoriations from scratching

⸻

Reinfection

Repeated infection is common because the eggs are easily transmitted within households.

The cycle may occur as:

Perianal itching → scratching → eggs under fingernails → hand-to-mouth transfer → reinfection

This is why hygiene measures and treatment of close contacts may be important.

⸻

Diagnosis

Diagnosis may be made by:

• Macroscopic identification of worms

• Detection of characteristic eggs using an adhesive tape preparation

The adhesive tape method is the classic diagnostic test.

⸻

Adhesive Tape Test

The test is performed by applying clear adhesive tape to the perianal skin, preferably early in the morning before bathing or defecation.

The tape is then examined microscopically for characteristic eggs.

Repeated sampling on several mornings may improve diagnostic yield.

⸻

Stool Examination

Adult worms may occasionally be visible macroscopically in stool.

However, routine stool microscopy is often less sensitive because eggs are deposited primarily on the perianal skin rather than directly into the stool.

⸻

Treatment

The source recommends:

Pyrantel pamoate 11 mg/kg orally as a single dose

Maximum dose:

1 g

Treatment should be repeated after 2 weeks.

⸻

Why Repeat Treatment?

The second dose is important because initial therapy kills the worms but may not eliminate all eggs.

A repeat dose approximately 2 weeks later helps eradicate worms that hatch after the first treatment.

⸻

Additional Treatment

Alternative regimens include:

Mebendazole 100 mg orally every 12 hours for 3 days

or

Albendazole 400 mg orally as a single dose

As with pyrantel pamoate, repeat treatment is often used to reduce recurrence.

⸻

Household Treatment

Treatment of the entire household should be considered, especially when more than one family member is infected.

This strategy helps interrupt the cycle of repeated transmission and reinfection.

⸻

Prevention

Good personal hygiene is the major preventive measure.

Important practices include:

• Frequent handwashing

• Washing hands after toileting and before eating

• Keeping fingernails short

• Avoiding nail biting

• Avoiding scratching the perianal region

• Washing bedding and clothing

• Regular bathing

• Cleaning frequently touched household surfaces

⸻

High-Yield Clinical Pattern

Child with intense nocturnal perianal itching

Possible household spread

Eggs detected by adhesive tape test

→ Think Enterobius vermicularis

⸻

Exam Essentials

Organism: Enterobius vermicularis

Type: Intestinal nematode

Disease: Enterobiasis / pinworm / oxyuriasis

Distribution: Worldwide

Life cycle: Approximately 2–6 weeks

Transmission: Fecal–oral ingestion of eggs

Classic symptom: Nocturnal perianal pruritus

Classic diagnostic test: Adhesive tape test

First-line treatment in source: Pyrantel pamoate

Important treatment principle: Repeat dose after 2 weeks

Alternatives: Mebendazole or albendazole

Household management: Consider treating close family members

Prevention: Good personal hygiene

⸻

Key clinical pearl: The classic association is child + nighttime perianal itching + positive adhesive tape test = Enterobius vermicularis, and treatment should usually be repeated after 2 weeks because reinfection is common.