Mycoplasma and Ureaplasma Flashcards
General features and habitat of Mycoplasma pneumoniae
No peptidoglycan cell wall- no Gram staining
Smallest bacteria
Not part of normal flora, but can be asymptomatic carriage in the respiratory tract
Biochemical Properties of Mycoplasma pneumoniae
Sterol in cytoplasm membrane- stabilize and allow flexibility
Obligate aerobe
Pathogenesis of Mycoplasma pneumoniae
Transmitted by respiratory droplets (inhaled aerosols)
Commonly affects people living in close quarters like military recruits
Commonly affects young adults (< 30 years old)
Surface parasite- not invasive (lack many metabolic enzymes, thus parasitic “life-style”)
Attaches to respiratory epithelium via P1 protein
Inhibits ciliary action- produces hydrogen peroxide, superoxide radicals, and cytolytic
enzymes, which damage the respiratory epithelium
This leads to necrosis and a bad, hacking cough (atypical pneumonia)
M. pneumoniae functions as superantigen, elicits production of IL-1, IL-6, and TNF-alpha
Clinical Features of
Atypical
(“Walking”) Pneumonia
X-ray shows patchy infiltrate
Atypical (“Walking”) Pneumonia- less severe symptoms than a regular pneumonia
Other diseases and symptoms:
Acute tracheobronchitis or acute pharyngitis
Chronic dry (hacking) cough
General symptoms- e.g. fever (but patient looks better than symptoms suggests)
Diagnosis of Mycoplasma pneumoniae
Specimens- blood (serum), urine or bronchoalveolar lavage (BAL)
Eaton’s agar- contain sterol for growth, showing “fried-egg” colonies
Cold agglutination- Ab agglutinins (IgM) are binding RBC at cold temperatures (~4C) Not used anymore since it is insensitive and non-specific
Serology- antibody detection by complement fixation
PCR- excellent sensitivity but not specific (cross-react with other species)
Treatment of Mycoplasma pneumoniae
Intrinsically (naturally) resistant to antibiotics inhibiting the cell wall synthesis
Macrolides (e.g. Erythromycin or Azithromycin)
Tetracycline (for ~2 weeks)
Beta-lactam antibiotics do not work since the bacteria lack cell wall
Mycoplasmatales
The smallest free-living bacteria organisms (once was confused to be a virus).
Mycoplasmatales genera
Eperythrozoon, Haemobartonella, Mycoplasma, and Ureaplasma.
The most clinically significant genera are Mycoplasma (125 species) and Ureaplasma (7 species).
The most important species is Mycoplasma pneumoniae (also called Eaton agent after the investigator who originally isolated it).
General Features of Mycoplasmatales
Mycoplasmas are facultative anaerobes (except M. pneumoniae, which is an obligate aerobe)
Grow slowly and require exogenous sterols supplied by animal serum added to the growth medium
Most form small colonies that are difficult to detect without extended incubation
Do not have a cell wall
Their major antigenic determinants are membrane glycolipids and proteins, but these antigens cross-react with human tissues and other bacteria,
thus impair specificity when trying to detect
M. genitalium
Habitat: genitourinary tract
Pathogenesis: transmitted by sexual contact (STD)
Diseases: non-gonococcal urethritis (NGU), pelvic inflammatory disease (PID)
Culture: from first part of urine or from ejaculate (urethral discharge)
M. hominis
Habitat: genitourinary tract, respiratory tract
Pathogenesis: transmitted by sexual contact (STD)
Diseases: non-gonococcal urethritis (NGU), pyelonephritis, postpartum fevers, systemic infections in immunocompromised patients
Culture: metabolize arginine, require 1-4 days
Treatment: Clindamycin is used, resistant to Erythromycin and occasionally to the Tetracycline (unlike the other mycoplasmas)
Ureaplasma
Ureaplasma urealyticum
Habitat: respiratory tract, genitourinary tract
Pathogenesis: transmitted by sexual contact (STD)
Diseases: Non-gonococcal urethritis (NGU), pyelonephritis, spontaneous abortion, premature birth
Culture: urea containing media (hence the name)- all the bacteria in the genus are urea + positive
Treatment: Erythromycin is used to treat Ureaplasma infections because these organisms are resistant to Tetracycline
