Spirochetes: Structure, Pathogenesis, and Clinical Importance.PPTX

This presentation provides a comprehensive overview of Spirochetes, a unique group of spiral-shaped bacteria responsible for several significant human and animal diseases. The slides cover their morphology, classification, pathogenic species (Treponema, Borrelia, and Leptospira), modes of transmission, clinical manifestations, diagnostic techniques, and treatment options. Special focus is given to their role in diseases such as syphilis, Lyme disease, and leptospirosis.

Designed for medical, microbiology, and laboratory technology students, this PPT is ideal for teaching, self-study, and academic discussions.

1. Spirochetes Azka Imran Mphil Pathology

2. Introduction Spirochetes are a unique group of bacteria characterized by their distinctive helical (spiral or corkscrew-like) morphology and unique mode of motility. They belong to the phylum Spirochaetota (formerly Spirochaetes ) and are Gram-negative, though their cell wall differs from classical Gram-negative bacteria. They are thin, flexible, and tightly or loosely coiled organisms, adapted to live in viscous environments such as mucus, connective tissue, and host fluids . Many spirochetes are free-living, but several species are important human pathogens, causing diseases such as syphilis, Lyme disease, and relapsing fever .

3. spiral or corkscrew

4. General Characteristics Shape and Structure Long, thin, spiral-shaped bacteria (0.1–0.6 µm in diameter; 3–500 µm in length). Flexible cell wall with a peptidoglycan layer and an outer sheath resembling Gram-negative bacteria. Helical morphology gives them a corkscrew-like appearance . Motility Motility is unique because of endoflagella (axial filaments) located in the periplasmic space (between the cell wall and outer membrane). These flagella run along the length of the organism, allowing rotation and a corkscrew-like motion. This enables movement in viscous fluids and tissues, which ordinary flagella-driven bacteria cannot penetrate.

5. Staining Too thin to be visualized by routine Gram staining. Can be observed using dark-field microscopy , phase-contrast microscopy , or special stains like silver impregnation . Fluorescent antibody techniques or PCR are used for laboratory diagnosis. Metabolism Most are microaerophilic or anaerobic . Some are free-living (aquatic), others are host-dependent.

6. Classification Spirochetes are divided into several medically important genera: Treponema Includes Treponema pallidum , the causative agent of syphilis . Other species cause yaws, pinta , and endemic syphilis. Cannot be cultured on artificial media; requires animal models. Borrelia Larger and more loosely coiled. Borrelia burgdorferi → causes Lyme disease . Borrelia recurrentis → causes relapsing fever (louse-borne or tick-borne).

7. Leptospira Thin, tightly coiled with hooked ends. Leptospira interrogans → causes leptospirosis (Weil’s disease). Found in animal reservoirs (especially rodents, dogs, cattle); transmitted via urine-contaminated water. Brachyspira Causes intestinal infections in animals (e.g., swine dysentery due to Brachyspira hyodysenteriae ).

8. Pathogenesis and Diseases Treponema pallidum (Syphilis): Sexually transmitted infection progressing through primary, secondary, latent, and tertiary stages. Borrelia burgdorferi (Lyme disease): Transmitted by Ixodes ticks; causes erythema migrans , arthritis, and neurological symptoms. Borrelia recurrentis (Relapsing fever): Characterized by recurrent episodes of fever due to antigenic variation. Leptospira interrogans (Leptospirosis): Causes jaundice, renal damage, meningitis, and hemorrhage (Weil’s syndrome).

9. Laboratory Diagnosis Direct detection: Dark-field microscopy (for Treponema in syphilis chancre fluid). Serological tests: VDRL, RPR, FTA-ABS for syphilis; ELISA and Western blot for Lyme disease. Culture: Leptospira can be cultured in special media ( Ellinghausen –McCullough–Johnson–Harris medium). Molecular techniques: PCR for species confirmation.

10. Clinical Importance Spirochetes are important due to the chronic, often systemic diseases they cause. Their ability to invade tissues and evade the immune system through antigenic variation makes them difficult to eradicate. Many spirochetal infections require prolonged antibiotic therapy (e.g., penicillin for syphilis, doxycycline for Lyme disease and leptospirosis).