General Characteristics
- Pleomorphic:
- Pear-shaped or filamentous rod
- Colonies have characteristic “fried egg” shape.
- Cell membrane is composed of sterol: Sterol supplementation is required for growth in a laboratory.
- No cell wall: therefore, does not gram stain
- Requires growth media enriched with nucleic acids to grow
- Smallest free-living bacteria
“Fried-egg” appearance of Mycoplasma hominis colonies
Image: “Gram-negative Mycoplasma hominis” by the CDC/ Dr. E. Arum. License: Public domain.
Scanning electron microscope image of M. pneumoniae, a pleomorphic bacterium lacking a cell wall, seen here in its filamentous form
Image: “Mycoplasma pneumoniae” by Rottem et al. License: CC BY 3.0, edited by Lecturio.
Pathogenesis
- Virulence factors:
- P1 adherence protein: promotes adherence to the respiratory epithelium
- Creation of reactive oxygen species: damages the respiratory epithelium
- Reservoirs:
- Humans:
- Asymptomatic carriers
- Symptomatic infected
- Humans:
- Transmission:
- Human-to-human transmission
- M. pneumoniae: inhalation of aerosolized droplets and contact with fomites
- M. hominis and M. genitalium: sexual contact
- Infected vectors are contagious for approximately 10 days from infection.
- Transmission requires prolonged periods of close contact.
- Human-to-human transmission
- High-risk factors:
- Age, primarily young adults
- Those living in close quarters:
- Military recruits
- Prisoners
Mechanisms of pathogenesis: Mycoplasma pneumoniae
Image by Lecturio. License: CC BY-NC-SA 4.0
Mechanisms of pathogenesis: Mycoplasma pneumoniae
Image by Lecturio. License: CC BY-NC-SA 4.0Diseases Caused by Mycoplasma
M. pneumoniae
Pathology caused by the M. pneumoniae bacterium is varied; however, diagnosis and treatment are standard:
- Respiratory infection:
- Atypical, or “walking” pneumonia:
- Insidious-onset headache, malaise, low-grade fever, and non-productive cough
- May be associated with autoimmune hemolytic anemia
- Tracheobronchitis (bronchitis):
- Inflammation of bronchi
- Presents with non-productive cough, fever, headache, sore throat, pharyngeal exudates, and cervical lymphadenopathy
- Pharyngitis:
- May precede pneumonia
- Milder presentations of M. pneumoniae infection
- Resembles pharyngitis produced by non-exudative group A Streptococcus infections or viral pharyngitis
- Atypical, or “walking” pneumonia:
- Mucocutaneous syndrome:
- Mild urticarial rash
- Erythema multiforme
- Stevens-Johnson syndrome
- M. pneumoniae–induced rash and mucositis (MPAM)
- Central nervous system (CNS) involvement:
- Direct infection: meningitis
- Post-infective autoimmune inflammatory processes caused by cross-reaction of Mycoplasma antibodies with galactocerebroside:
- Acute disseminated encephalomyelitis (ADEM)
- Guillain-Barre
- Hemolysis:
- Infection causes alteration of I antigen on red blood cells → leads to immunoglobulin (IgM) production and autoimmune hemolysis
- Seen in 60% of infections
- Usually self-limited, not requiring treatment
- Diagnosis:
- Clinical picture usually sufficient
- Lab testing:
- Culture: grows on Eaton agar, but usually the polymerase chain reaction (PCR) is more sensitive
- High titer of cold agglutinin (IgM)
- Nucleic acid amplification (PCR)
- Chest X-ray: diffuse interstitial infiltrates with no alveolar exudates (appear worse than expected compared to clinical symptoms)
- Treatment:
- Macrolides, tetracyclines, or respiratory fluoroquinolones
- Penicillins (and other cell wall synthesis inhibitors) are ineffective because Mycoplasma have no cell wall.
M. pneumoniae-associated mucositis (MPAM): Erosive oral lesions are limited to the mucosa in this form of MPAM in a 24-year-old woman.
Image: “MPAM” by the Department of Pediatrics, Division of Pediatric Infectious Diseases and Immunology, Erasmus MC-Sophia Children’s Hospital, University Medical Center Rotterdam, Netherlands. License: CC BY 4.0.
Mycoplasma pneumoniae pneumonia in a human. A: Chest X-ray shows infiltrates in the right lower lobe.
Image: “Mycoplasma pneumoniae pneumonia in human” by the NPO Sapporo Cough, Asthma, and Allergy Center Sapporo, Japan. License: CC BY 4.0
B: consolidation (∗) and bronchovascular bundles thickening (↑) on computed tomography (CT) scan
| Characteristics | Mycoplasma pneumonia | Pneumococcal pneumonia |
|---|---|---|
| Type of pneumonia | Atypical (interstitial) | Typical (alveolar) |
| Preceding pharyngitis | Common | Never |
| Onset | Gradual | Sudden with chills |
| Fever | Low grade | High grade |
| Cough | Non-productive, paroxysmal | Productive |
| Pleuritic chest pain | Absent | Present |
| Leukocytosis | Absent | Present |
| Age of highest incidence | Young adults < 30 years old | Older adults |
| Complications | Otitis media, erythema multiforme, hemolytic anemia, myocarditis, pericarditis, bullous otitis media | Bacteremia, meningitis, otitis media |
Mycoplasma hominis, Mycoplasma genitalium
- Less common, known to cause disease of the urogenital tract:
- Pyelonephritis
- Pelvic inflammatory disease (PID)
- Postabortal fever
- Postpartum fever
- Diagnosis:
- Clinical suspicion in at-risk patients:
- Immunocompromised
- Preterm infants
- Concomitant sepsis
- Laboratory testing:
- Culture: difficult and slow to grow
- PCR testing: more rapid, but performed in few specialized centers
- Clinical suspicion in at-risk patients:
- Treatment:
- Tetracyclines
- Fluoroquinolones
- Clindamycin
References
- Kashyap, S., & Sarkar, M. (2010). Mycoplasma pneumonia: Clinical features and management. Lung India: Official organ of Indian Chest Society, 27(2), 75–85. https://doi.org/10.4103/0970-2113.63611
- Waites, K.B., & Taylor-Robinson, D. (2015). Mycoplasma and Ureaplasma. In the Manual of Clinical Microbiology, 11th ed, Jorgensen, J., Pfaller, M., Carroll, K., et al. (Eds), ASM Press, Washington DC. P. 1088.
- Baseman, J.B., & Tully, J.G. (1997). Mycoplasmas: Sophisticated, reemerging, and burdened by their notoriety. Emerg Infect Dis. Jan-Mar;3(1):21-32. doi: 10.3201/eid0301.970103. PMID: 9126441; PMCID: PMC2627593.
- Koskiniemi, M. (1993). CNS manifestations associated with Mycoplasma pneumoniae infections: Summary of cases at the University of Helsinki and review. Clin Infect Dis. Aug;17 Suppl 1(Suppl 1):S52-7. doi: 10.1093/clinids/17.supplement_1.s52. PMID: 8399938; PMCID: PMC7110383.
