Chapter 16: Mycoplasma: Atypical Bacterial Pathogens

Distinguished by their complete lack of a peptidoglycan cell wall, these microbes are instead enclosed by a flexible, sterol-containing lipid bilayer, making them naturally resistant to common antibiotics like penicillins and cephalosporins that target cell wall synthesis. Their extremely small genome size and fastidious nature—requiring external sources of cholesterol for growth—pose significant challenges for clinical cultivation and laboratory identification. The primary pathogen discussed is Mycoplasma pneumoniae, the agent behind atypical or "walking" pneumonia, which typically presents with a gradual onset of fever, headache, and a persistent dry cough. This organism utilizes a specialized P1 adhesin to attach to the ciliated epithelial cells of the respiratory tract, leading to localized inflammation and tissue damage via an exotoxin similar to that of pertussis. Beyond respiratory issues, the chapter delves into urogenital species like Mycoplasma hominis, often associated with postpartum fever and pelvic inflammatory disease, and Ureaplasma urealyticum, which is recognized for its ability to hydrolyze urea and contribute to nongonococcal urethritis in men and complications during pregnancy for women. Mycoplasma genitalium is further identified as a significant sexually transmitted pathogen causing syndromes similar to those of gonococcus or chlamydia. Diagnostic strategies have shifted away from difficult cultures and cold agglutinin serology toward advanced molecular techniques like polymerase chain reaction. Therapeutic management emphasizes the use of tetracyclines, macrolides, or fluoroquinolones, though the text highlights critical resistance patterns, such as the inherent resistance of certain species to erythromycin or emerging resistance to common first-line treatments for urogenital infections.