39. Mycoplasma spp. Classification. Morphology, biology, diseases. Microbiological diagnosis. L-forms of bacteria. Chlamydia. General characteristics. The causative agent of psittacosis and trachoma. Morphology and biology. Pathogenesis and disease. Microbiological diagnosis. Chlamydia as causative agents of sexually transmitted diseases. Therapy.

I. General Characteristics

• Smallest free-living bacteria (0.1–0.3 μm).
• Lack a cell wall: not visible on Gram stain, pleomorphic (variable shape).
• Triple-layered membrane contains sterols (unusual for bacteria — taken from host).
• Resistant to β-lactam antibiotics (penicillins, cephalosporins).
• Facultative anaerobes or aerobes.
• Fastidious: grow slowly on enriched media with sterols (e.g. SP4 medium).
• Includes:
• Mycoplasma pneumoniae – respiratory pathogen.
• Mycoplasma hominis, Mycoplasma genitalium – urogenital infections.
• Ureaplasma urealyticum – part of normal flora; causes genital and perinatal infections.

III. Virulence Factors

• Adhesins: e.g., P1 protein in M. pneumoniae — binds to respiratory epithelium (sialic acid).
• Hydrogen peroxide production: damages host cell membranes.
• Ciliostasis: interferes with mucociliary clearance.
• Urease activity (in Ureaplasma): hydrolyzes urea → ammonia → cytotoxic effects on uroepithelium.
• Surface antigen variation: immune evasion.
• Induces autoimmune responses due to antigen mimicry (e.g., cold agglutinins in M. pneumoniae).

IV. Epidemiology

• Reservoir: Humans — respiratory and genitourinary tract.
• Transmission:
• M. pneumoniae: respiratory droplets (crowded environments, schools, military).
• Ureaplasma / M. hominis: sexual contact, vertical transmission during delivery.
• Common in young adults and adolescents.

• Normal flora: Ureaplasma and M. hominis are found in ~40–80% of sexually active women.