32. Mycoplasma spp. Classification. Morphology, biology, diseases. Microbiological diagnosis. L-forms of bacteria. Chlamydia. General characteristics. Species. Morphology and biology. Pathogenesis and disease. Microbiological diagnosis. Pathogenic fungi.

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.