Infectious Disease and Microbiology – Mycoplasma Species

Overview

Mycoplasma species are extremely small, pleomorphic bacteria that lack a cell wall. This absence of peptidoglycan is their defining microbiologic feature and explains why β-lactam antibiotics such as penicillins and cephalosporins are ineffective.

Many Mycoplasma species exist as commensal organisms of human mucosal surfaces. Clinically, Mycoplasma pneumoniae is most important as a respiratory pathogen, while M. genitalium and M. hominis are associated primarily with the genitourinary tract.

Classification

Genus: Mycoplasma

Species listed in the source include:

• M. buccale

• M. faucium

• M. felis

• M. genitalium

• M. hominis

• M. laidlawii

• M. lipophilum

• M. oculi

• M. orale

• M. penetrans

• M. pirum

• M. pneumoniae

• M. primatum

• M. salivarium

• M. spermatophilum

• M. urealyticum

Taxonomic Note

The organism historically called:

Mycoplasma urealyticum

is now classified as:

Ureaplasma urealyticum

It shares the important characteristic of lacking a conventional bacterial cell wall.

Microbiologic Characteristics

Mycoplasma species are:

• Very small bacteria

• Without a cell wall

• Pleomorphic

• Surrounded only by a cell membrane

• Poorly visualized by conventional Gram staining

Because there is no rigid peptidoglycan layer, these organisms can assume variable shapes.

The Most Important Feature – No Cell Wall

The absence of a cell wall has major therapeutic implications.

Antibiotics that inhibit cell-wall synthesis have no appropriate target.

Therefore:

Penicillins

• ●

Cephalosporins

• ●

Other β-lactam antibiotics

→ Ineffective against Mycoplasma

High-Yield Microbiology Pattern

Extremely small bacterium

• ●

No cell wall

• ●

Pleomorphic

• ●

Does not stain well with Gram stain

• ●

Intrinsically resistant to β-lactams

→ Think Mycoplasma

Epidemiology

Mycoplasma species occur:

Worldwide

Many are commensal organisms that may be recovered from healthy human mucosal surfaces.

Therefore, isolation of some species does not necessarily establish that they are causing disease.

Major Sites

M. pneumoniae

→ Respiratory tract

M. hominis

→ Genitourinary tract

M. genitalium

→ Genitourinary tract and sexually transmitted infection

Mycoplasma pneumoniae

M. pneumoniae is the major respiratory pathogen in this genus and is a classic cause of:

Atypical pneumonia

It also causes several upper and lower respiratory tract syndromes.

Incubation Period

The source gives an incubation period of:

6–32 days

for clinical syndromes caused by M. pneumoniae.

The relatively long incubation period allows gradual transmission within households and other close-contact populations.

Transmission

M. pneumoniae is transmitted mainly through:

Respiratory droplets

Close and prolonged interpersonal contact facilitates transmission.

Epidemiologic Pattern

Respiratory infection is particularly common among:

Older children, adolescents, and young adults

The source emphasizes patients approximately:

10–40 years old

Infections can occur:

• Sporadically

• Endemically

• In outbreaks or epidemics

Disease occurs throughout the year.

Outbreak Settings

Transmission may be facilitated in:

• Schools

• Dormitories

• Military barracks

• Households

• Other crowded living environments

Respiratory Infections

M. pneumoniae can cause:

• Pneumonia

• Bronchitis

• Tracheobronchitis

• Pharyngitis

• Sinusitis

• Myringitis

Atypical Pneumonia

The classic respiratory syndrome is:

Atypical or “walking” pneumonia

Patients often develop a gradually progressive illness rather than the abrupt presentation typical of some bacterial pneumonias.

Clinical Manifestations

Typical manifestations include:

• Fever

• Malaise

• Headache

• Sore throat

• Persistent dry cough

• Bronchitis

• Pneumonia

The cough can persist for a prolonged period.

High-Yield Respiratory Pattern

Adolescent or young adult

• ●

Gradual respiratory illness

• ●

Persistent dry cough

• ●

Atypical pneumonia

→ Think Mycoplasma pneumoniae

Extrapulmonary Manifestations

Although M. pneumoniae primarily causes respiratory disease, rare extrapulmonary complications include:

• Hemolytic anemia

• Pericarditis

• Myocarditis

• Meningoencephalitis

• Erythema multiforme

• Hepatitis

Some complications may result from immune-mediated mechanisms.

Cold Agglutinin Hemolytic Anemia

A classic association of M. pneumoniae is:

Cold agglutinin-associated hemolytic anemia

Antibodies generated during infection can react with red blood cells at lower temperatures and produce agglutination and hemolysis.

High-Yield Association

M. pneumoniae

→ Cold agglutinins

→ Red-cell agglutination

→ Hemolytic anemia

This is an important exam association, although cold agglutinin testing is neither sufficiently sensitive nor specific to be the preferred modern diagnostic method.

Cardiac Disease

Rare cardiac manifestations include:

Myocarditis

and

Pericarditis

Neurologic Disease

Rare neurologic complications include:

• Encephalitis

• Meningitis

• Meningoencephalitis

Dermatologic Disease

M. pneumoniae may be associated with:

Erythema multiforme

and other mucocutaneous inflammatory syndromes.

Myringitis

M. pneumoniae has historically been associated with:

Bullous myringitis

However, bullous myringitis is not specific for M. pneumoniae and can occur with other respiratory pathogens.

Mycoplasma genitalium

M. genitalium is an important sexually transmitted pathogen.

It is associated with:

• Nongonococcal urethritis

• Persistent or recurrent urethritis

• Cervicitis

• Pelvic inflammatory disease

High-Yield STI Pattern

Sexually active patient

• ●

Persistent/recurrent nongonococcal urethritis

→ Consider Mycoplasma genitalium

Pelvic Inflammatory Disease

M. genitalium can infect the female reproductive tract and has been associated with:

Pelvic inflammatory disease

Persistent reproductive tract infection may potentially contribute to reproductive complications.

Mycoplasma hominis

M. hominis is primarily associated with the:

Genitourinary tract

It may be recovered as part of normal genital flora but can also participate in clinically significant infection.

Salpingitis

The source reports isolation of M. hominis from the:

• Endometrium

• Fallopian tubes

in approximately 10% of women with salpingitis.

However, because salpingitis and pelvic inflammatory disease are frequently:

Polymicrobial

the presence of M. hominis does not necessarily prove that it is the primary pathogen.

Mycoplasma fermentans

The source associates M. fermentans with uncommon reports of:

• Pneumonia

• Encephalitis

• Hepatitis

• Myopericarditis

• Sepsis

• Diarrhea

Its role in human disease is less firmly established than that of M. pneumoniae or M. genitalium.

Infertility

Some studies have suggested possible associations between genital Mycoplasma species and:

Infertility

However, interpretation is complicated because several species can colonize the genital tract without producing disease.

Therefore:

Detection does not automatically equal causation.

Diagnosis

The source lists:

• Culture

• Serology

• Detection of cold agglutinins

• PCR of respiratory specimens for M. pneumoniae

PCR and NAAT

Molecular testing is particularly useful because Mycoplasma organisms can be difficult or slow to culture.

For M. pneumoniae:

PCR/NAAT of respiratory specimens

can provide direct evidence of infection.

For M. genitalium:

NAAT is the major diagnostic approach

because routine culture is extremely difficult.

Culture

Mycoplasma species require specialized culture conditions.

Some species grow slowly, making culture less useful for rapid clinical diagnosis.

Classic Culture Appearance

A traditional microbiologic association is:

“Fried-egg” colonies

on specialized culture media.

Serology

Serology may assist in diagnosing M. pneumoniae infection, particularly when interpreted with the timing and clinical presentation.

Cold Agglutinins

The source lists:

Cryoagglutinin/cold agglutinin testing

for M. pneumoniae.

This is primarily a historical or supportive clue rather than a definitive modern diagnostic test.

Treatment

The source lists:

Doxycycline 100 mg orally every 12 hours for 7–14 days

as treatment.

Other active antibiotic classes include:

• Macrolides

• Fluoroquinolones

The appropriate drug depends on the species, clinical syndrome, patient factors, and resistance patterns.

Treatment of M. pneumoniae

The source lists:

Macrolides

or

Fluoroquinolones

as additional treatments for M. pneumoniae infection.

Doxycycline is another important active agent.

Major Treatment Principle

Because Mycoplasma lacks a cell wall:

β-lactams do NOT work.

This includes:

• Penicillin

• Amoxicillin

• Ampicillin

• Cephalosporins

• Carbapenems

Why β-Lactams Fail

β-lactam

↓

Inhibits peptidoglycan cell-wall synthesis

↓

Mycoplasma has no peptidoglycan cell wall

↓

No therapeutic target

↓

Intrinsic resistance

Mycoplasma genitalium and Resistance

M. genitalium has become particularly important because antimicrobial resistance can complicate treatment.

Resistance may involve:

Macrolides

and

Fluoroquinolones

Therefore, treatment of confirmed M. genitalium infection should follow appropriate current guideline- or resistance-guided regimens rather than assuming that all isolates will respond to the same antibiotic.

Mycoplasma pneumoniae vs. Typical Bacterial Pneumonia

M. pneumoniae

→ No cell wall

→ Atypical pneumonia

→ Gradual onset

→ Dry cough

→ Young patients/outbreak settings

→ Cold agglutinins

→ β-lactams ineffective

Streptococcus pneumoniae

→ Gram-positive diplococcus

→ Cell wall present

→ Typical community-acquired pneumonia

→ More abrupt presentation may occur

→ Productive cough may occur

→ Susceptible infections can respond to β-lactams

Mycoplasma vs. Ureaplasma

Mycoplasma

→ No cell wall

→ M. pneumoniae: respiratory disease

→ M. genitalium: urethritis/PID

→ M. hominis: genitourinary colonization/infection

Ureaplasma

→ Also lacks a cell wall

→ Primarily genitourinary

→ Characteristically hydrolyzes urea

Prevention

For respiratory M. pneumoniae infection, transmission may be reduced through:

• Respiratory hygiene

• Avoidance of prolonged close exposure to infected individuals

• Reduction of crowding when feasible

For sexually transmitted organisms such as M. genitalium:

• Condom use

• Safer sexual practices

• Appropriate evaluation and management of sexual partners

can reduce transmission.

High-Yield Clinical Pattern

Young patient

• ●

“Walking” atypical pneumonia

• ●

Persistent dry cough

• ●

Cold agglutinins

• ●

Organism without a cell wall

→ Think Mycoplasma pneumoniae

High-Yield Genitourinary Pattern

Persistent or recurrent nongonococcal urethritis

• ●

Sexual transmission

• ●

NAAT positive

→ Think Mycoplasma genitalium

Exam Essentials

Genus: Mycoplasma

Defining feature: NO CELL WALL

Morphology: Very small and pleomorphic

Gram stain: Poorly visualized

β-lactams: Intrinsically ineffective

Major respiratory species: M. pneumoniae

Major STI species: M. genitalium

Important genital species: M. hominis

M. pneumoniae incubation: 6–32 days in the source

Transmission: Respiratory droplets

Classic disease: Atypical “walking” pneumonia

Classic symptom: Persistent dry cough

Classic laboratory association: Cold agglutinins

Important complication: Hemolytic anemia

Other complications: Myocarditis, pericarditis, CNS disease, erythema multiforme, hepatitis

M. genitalium: Nongonococcal urethritis, cervicitis, PID

Diagnosis: PCR/NAAT particularly useful

Classic culture appearance: “Fried-egg” colonies

Source treatment: Doxycycline

M. pneumoniae alternatives: Macrolide or fluoroquinolone

Key therapeutic rule: Do not treat Mycoplasma with β-lactam antibiotics

Key clinical pearl: The single most important fact about Mycoplasma is that it has no cell wall, making β-lactam antibiotics ineffective. Remember M. pneumoniae for atypical “walking” pneumonia with a persistent dry cough and cold agglutinins, and M. genitalium for persistent or recurrent nongonococcal urethritis and pelvic inflammatory disease.