Mycoplasma Flashcards
What are the general characteristics of Mycoplasma species?
Mycoplasma are the smallest free-living bacteria in nature, about 100 nm in size, undetectable by light microscopy, and lack a cell wall. Their cell membrane is rich in sterol and other lipids.
Why don’t Mycoplasma species stain with Gram stain?
Because they lack a cell wall, although they are Gram-negative bacteria. Giemsa and Dienes stains are used instead.
What is the significance of Mycoplasma being pleomorphic?
Their lack of a rigid cell wall and small size allows them to be pleomorphic (no fixed shape or size) and to cross filters permeable only to viruses.
Which antibiotics are Mycoplasma resistant to, and which are they susceptible to?
Resistant to antibiotics that interfere with cell wall synthesis (e.g., Penicillin, Cephalosporin, Vancomycin). Susceptible to tetracycline and erythromycin.
Describe the colony morphology of Mycoplasma on agar.
Colonies have an opaque center and a transparent outer zone, giving a ‘fried-egg’ appearance (except M. pneumoniae, which shows granular, mulberry-shaped colonies).
What diseases are caused by Mycoplasma pneumoniae, Ureaplasma urealyticum, and M. genitalium?
M. pneumoniae: Atypical pneumonia (walking pneumonia) and tracheobronchitis. U. urealyticum: Non-gonococcal urethritis. M. genitalium: Non-gonococcal urethritis.
What is ‘walking pneumonia’?
A non-medical term for M. pneumoniae infection, indicating the disease is not severe enough to require bed rest or hospitalization.
How is Mycoplasma pneumoniae transmitted?
Through respiratory droplets, often in crowded environments like colleges, military barracks, or prisons.
What are the typical symptoms of M. pneumoniae infection?
Gradual onset of non-productive cough, sore throat, fever, and headache.
What is the role of P1 adhesin in M. pneumoniae virulence?
P1 protein (a cytoadhesin) allows M. pneumoniae to adhere tightly to host ciliated bronchial epithelial cells, inhibiting ciliary action and causing tissue desquamation and inflammation.
What specimens are ideal for culturing M. pneumoniae?
Throat swabs and nasopharyngeal aspirates.
Why is microscopy not very helpful for diagnosing Mycoplasma infections?
Due to their lack of a cell wall and small size, they are undetectable by routine light microscopy.
What molecular technique is best for diagnosing M. pneumoniae infection?
Polymerase chain reaction (PCR), which detects M. pneumoniae DNA earlier than serological tests.
What serological tests are used for Mycoplasma diagnosis?
Complement Fixation Test, ELISA, and Immunofluorescence.
What is the Cold Agglutination Test, and what does it detect?
A non-specific test that detects IgM autoantibodies against red blood cells at 4°C, previously used for Mycoplasma diagnosis.
What radiographic finding is typical in M. pneumoniae pneumonia?
The X-ray often looks worse than the clinical picture.
What are the treatment options for M. pneumoniae infection?
Erythromycin, clarithromycin, azithromycin, tetracycline (for patients >10 years), and levofloxacin. Treatment is bacteriostatic, not bactericidal.
Why is Mycoplasma pneumoniae pneumonia difficult to differentiate from viral diseases clinically?
Symptoms overlap, and laboratory tests (culture, serology, PCR) are needed for definitive diagnosis.
