38. Spirochetes (Spirochaetaceae). General characteristics. The causative agent of syphilis (Treponema pallidum). Morphology and biology. Pathogenesis and immunity. Microbiological diagnosis. Leptospira spp. Morphology and biology. Pathogenesis and immunity. Antigenic composition and serological types. Microbiological diagnosis. The causative agent of relapsing fever (Borrelia recurrentis). Morphology and biology. Pathogenesis and immunity. Microbiological diagnosis. The causative agent of Lyme Disease (Borrelia burgdorferi). Pathogenesis, immunity, microbiological diagnosis.

General Characteristics

• Spiral-shaped (spirochete), slender (0.1–0.2 μm) and flexible, 10–13 μm long
• Motile via endoflagella (axial filaments within periplasmic space)
• Cannot be seen with standard Gram stain – best visualized by:
• Dark-field microscopy
• Silver stain
• Fluorescent antibody techniques

• Cannot be cultured on artificial media
• Structurally complex – central protoplasmic cylinder bounded by a cytoplasmic membrane and cell wall of similar structure to that of Gram (–) bacteria
• Cultivated in rabbit testis for diagnostic strains:
• Nichol’s strain (pathogenic, used for diagnostic antigen production)
• Reiter’s strain (nonpathogenic, used for serologic testing)

Transmission

• Sexual contact through microabrasions
• Transplacental (congenital syphilis)
• Blood transfusion (rare)
• Occupational (healthcare workers – non-venereal)

Stages of Syphilis

• Gummatous syphilis (soft granulomas)
• Cardiovascular syphilis (aortic aneurysm)

• Neurosyphilis: Tabes dorsalis, general paresis, dementia

Congenital, Transplacental. Signs: saddle nose, Hutchinson’s teeth, deafness, blindness, keratitis.

Laboratory Diagnosis

1. Microscopy

• Dark-field or phase-contrast microscopy of fluid from chancre
• Silver staining (Levaditi) in tissue biopsies

Serology

A. Nontreponemal Tests (screening)

⚠️ False positives: HIV, pregnancy, autoimmune diseases, malaria, endocarditis

B. Treponemal Tests (confirmatory)