Infectious Disease and Microbiology – Sphingobacterium Species

Overview

Sphingobacterium species are uncommon aerobic Gram-negative bacilli that are widely distributed in the environment but only rarely cause human disease. Important species include Sphingobacterium multivorum and Sphingobacterium spiritivorum.

Human infections are usually opportunistic and healthcare-associated, particularly in patients with significant underlying disease, immunocompromise, prolonged hospitalization, or invasive medical devices. Reported infections include bacteremia, peritonitis, pneumonia and other respiratory infections, urinary tract infections, and skin and soft-tissue infections.

Classification

Genus: Sphingobacterium

Important species include:

• Sphingobacterium multivorum

• Sphingobacterium spiritivorum

• Other Sphingobacterium species

Microbiologic Characteristics

Sphingobacterium species are:

• Aerobic Gram-negative bacilli

• Nonfermenting organisms

• Generally nonmotile

• Environmental bacteria

• Uncommon human pathogens

A distinctive feature of the genus is the presence of:

Sphingolipids within the bacterial cell membrane

which contributed to the name:

Sphingobacterium

High-Yield Microbiology Pattern

Aerobic Gram-negative bacillus

• ●

Nonfermenting environmental organism

• ●

Sphingolipids in cell membrane

• ●

Rare healthcare-associated infection

→ Think Sphingobacterium

Incubation Period

The incubation period is:

Unknown

Because most infections are opportunistic or healthcare-associated, there is no characteristic incubation period.

Epidemiology

Sphingobacterium species have a:

Worldwide distribution

However, human infections are:

Rare

The organisms can be encountered in environmental reservoirs, including:

• Soil

• Water

• Plants

• Moist environmental sites

Nosocomial Infection

The source emphasizes that Sphingobacterium species usually cause:

NOSOCOMIAL INFECTIONS

Healthcare-associated disease may be facilitated by:

• Prolonged hospitalization

• Critical illness

• Immunosuppression

• Invasive medical procedures

• Indwelling catheters

• Significant underlying disease

• Previous broad-spectrum antimicrobial exposure

High-Yield Epidemiologic Pattern

Hospitalized or medically complex patient

• ●

Unusual nonfermenting Gram-negative bacillus

• ●

Bacteremia, respiratory infection, or device-associated infection

→ Consider Sphingobacterium

Opportunistic Pathogenicity

Sphingobacterium is generally considered a:

Low-virulence opportunistic pathogen

Disease is therefore more likely when normal host defenses have been compromised.

Recovery from a clinical specimen should be interpreted according to:

Clinical syndrome + specimen source + host factors + repeated isolation

because environmental Gram-negative organisms may occasionally represent colonization or contamination.

Clinical Infections

Reported infections include:

• Peritonitis

• Bacteremia

• Skin and soft-tissue infection

• Respiratory tract infection

• Urinary tract infection

The severity ranges from localized disease to systemic infection.

Bacteremia

Sphingobacterium can cause:

Bloodstream infection

particularly in hospitalized or immunocompromised patients.

Potential sources may include:

• Intravascular devices

• Respiratory infection

• Urinary infection

• Soft-tissue infection

• Other healthcare-associated sources

High-Yield Bacteremia Pattern

Hospitalized patient

• ●

Fever or sepsis

• ●

Blood culture grows an unusual nonfermenting GNB

• ●

Sphingobacterium

→ Evaluate for true opportunistic bacteremia and a device-related source

Peritonitis

The organism can cause:

Peritonitis

This is particularly important when an invasive abdominal or dialysis-associated route provides access to the peritoneal cavity.

Diagnosis depends on compatible clinical findings and recovery of the organism from:

Peritoneal fluid

Respiratory Tract Infection

Sphingobacterium species have been associated with:

Respiratory tract infections

including lower respiratory disease in susceptible patients.

Potential manifestations include:

• Fever

• Cough

• Dyspnea

• Increased respiratory secretions

• Pulmonary infiltrates

Colonization vs. Respiratory Infection

Because unusual environmental Gram-negative organisms may colonize respiratory secretions, isolation from sputum alone does not always establish:

Pneumonia

Evidence supporting true infection includes:

Compatible symptoms

• ●

New pulmonary infiltrates

• ●

Inflammatory findings

• ●

Repeated or significant microbiologic isolation

Urinary Tract Infection

Sphingobacterium may cause:

Urinary tract infection

particularly in patients with:

• Urinary catheters

• Structural urinary abnormalities

• Repeated instrumentation

• Prolonged hospitalization

Clinical disease can range from:

Cystitis

to:

Complicated UTI or urosepsis

Skin and Soft-Tissue Infection

The organism can occasionally cause:

Skin and soft-tissue infections

particularly when normal skin barriers are disrupted by:

• Trauma

• Surgery

• Chronic wounds

• Medical procedures

Diagnosis

The principal diagnostic method is:

CULTURE

Appropriate specimens depend on the suspected site of infection.

These may include:

• Blood

• Urine

• Respiratory specimens

• Peritoneal fluid

• Wound or soft-tissue specimens

Laboratory Identification

Identification of uncommon nonfermenting Gram-negative bacilli can occasionally be challenging.

Modern laboratory techniques may assist in distinguishing Sphingobacterium from other environmental Gram-negative organisms.

For clinically significant isolates, accurate identification is important because:

Antimicrobial susceptibility patterns can be unpredictable.

Antimicrobial Susceptibility Testing

Treatment should ideally be based on:

Culture + antimicrobial susceptibility testing

because susceptibility may vary among species and individual isolates.

This is particularly important for:

Serious bloodstream or other invasive infections.

Treatment

The source lists:

Ampicillin

as the primary treatment.

However, because Sphingobacterium species can demonstrate variable antimicrobial susceptibility, a fixed empiric assumption of ampicillin susceptibility should be avoided.

Definitive therapy should be based on:

Individual susceptibility results.

Additional Treatment Options

The source lists the following potential agents:

• Trimethoprim–sulfamethoxazole

• Fluoroquinolones

• Third-generation cephalosporins

• Carbapenems

These should be considered:

Only when the clinical isolate is susceptible.

Resistance Considerations

Sphingobacterium species may possess resistance mechanisms affecting several antimicrobial classes.

Therefore:

Species identification alone does not reliably predict susceptibility.

This makes laboratory susceptibility testing particularly valuable when treating invasive disease.

High-Yield Treatment Principle

Sphingobacterium infection

→ Obtain appropriate culture

• ●

Perform susceptibility testing

• ●

Select an active antimicrobial

• ●

Control any infected device or anatomical source

Source Control

As with other opportunistic healthcare-associated Gram-negative infections, management should include evaluation for an:

Infected catheter, device, wound, or other persistent source

Examples include:

Bacteremia + central line

→ Evaluate the line as a possible source

UTI + urinary catheter

→ Remove or replace unnecessary catheter when appropriate

Peritonitis + indwelling device

→ Evaluate the device and associated source

Soft-tissue infection

→ Drain or debride infected collections when necessary

Sphingobacterium vs. Pseudomonas aeruginosa

Both may appear as:

Nonfermenting Gram-negative bacilli

and can cause healthcare-associated infections.

However:

Pseudomonas aeruginosa

→ Much more common human pathogen

→ Motile

→ Oxidase positive

→ Characteristic pigments may occur

→ Major cause of severe nosocomial infection

Sphingobacterium

→ Rare opportunistic pathogen

→ Generally nonmotile

→ Environmental organism

→ Characteristically contains sphingolipids

Sphingobacterium vs. Acinetobacter

Both can cause:

Healthcare-associated opportunistic infections

and may infect critically ill patients.

Acinetobacter

→ Gram-negative coccobacillus

→ Nonmotile

→ Important multidrug-resistant nosocomial pathogen

Sphingobacterium

→ Gram-negative bacillus

→ Rare human pathogen

→ Environmental organism with membrane sphingolipids

Prevention

There is no specific vaccine.

Prevention focuses on general healthcare infection-control practices, including:

• Hand hygiene

• Appropriate catheter care

• Limiting unnecessary invasive devices

• Proper respiratory equipment management

• Environmental cleaning

• Appropriate wound care

• Antimicrobial stewardship

High-Yield Clinical Pattern

Hospitalized/immunocompromised patient

• ●

Bacteremia, peritonitis, pneumonia, UTI, or soft-tissue infection

• ●

Rare aerobic nonfermenting Gram-negative bacillus

• ●

Environmental organism containing sphingolipids

→ Think SPHINGOBACTERIUM

Exam Essentials

Genus: Sphingobacterium

Important species: S. multivorum and S. spiritivorum

Organism: Aerobic Gram-negative bacillus

Metabolism: Generally nonfermenting

Motility: Generally nonmotile

Distinctive feature: Sphingolipids in the cell membrane

Distribution: Worldwide

Frequency: Rare human pathogen

Major epidemiologic setting: Nosocomial/healthcare-associated infection

Major infections: Bacteremia, peritonitis, respiratory infection, UTI, and skin/soft-tissue infection

Diagnosis: Culture

Important laboratory principle: Perform antimicrobial susceptibility testing

Source-listed treatment: Ampicillin

Additional source-listed agents: TMP-SMX, fluoroquinolones, third-generation cephalosporins, and carbapenems

Modern treatment principle: Use susceptibility-guided therapy because resistance patterns can vary

Management principle: Antimicrobial treatment plus source control when a device or localized focus is involved

Key clinical pearl: Sphingobacterium species are rare environmental, nonfermenting Gram-negative bacilli characterized by sphingolipids in their cell membranes. They primarily behave as opportunistic healthcare-associated pathogens, causing bacteremia, peritonitis, respiratory infection, UTI, and skin or soft-tissue disease. Because antimicrobial susceptibility can be variable, a clinically significant isolate should be treated according to culture and susceptibility results rather than assuming that a particular antibiotic will be active.