A 34-year-old pregnant woman at 28 weeks gestation is found to have a positive treponemal test (TPHA) but negative non-treponemal test (VDRL) during routine antenatal screening. She has no history of syphilis treatment. What is the most appropriate interpretation and management?

Latent syphilis cannot be ruled out - treat with benzathine penicillin

Successfully treated past infection - no treatment needed

Biological false positive - repeat testing in 4 weeks

False positive TPHA - no treatment needed

Which of the following bacteria does not exhibit bipolar staining?

Calymmatobacterium granulomatis

What is the significance of prozone phenomenon in syphilis testing?

False negative result in high-titer secondary syphilis

False negative result in early primary syphilis

False positive result in treated syphilis

False positive result in pregnancy

What is the main mechanism by which Treponema pallidum causes tissue damage in tertiary syphilis?

Delayed hypersensitivity reaction

Endotoxin-mediated inflammation

Spirochetes for FMGE: High-Yield Microbiology Lessons

Spirochetes: Overview - Twisty Troublemakers

General Characteristics:
- Gram-negative, thin, flexible, spiral/helical-shaped bacteria.
- Possess endoflagella (axial filaments) in periplasmic space, enabling corkscrew motility.
Classification: Order Spirochaetales.
Microscopy:
- Difficult to visualize with Gram stain (too thin).
- Dark-field microscopy: Essential for live, unstained organisms.
- Silver impregnation stains: (e.g., Fontana-Tribondeau, Levaditi) for tissue sections.
- Giemsa or Wright stain: For Borrelia in blood smears.

Spirochete structure diagram

⭐ Spirochetes are notoriously difficult to Gram stain due to their thin cell wall and are best visualized using dark-field microscopy or special stains like silver impregnation (e.g., Fontana-Tribondeau).

Treponema: Syphilis - The Great Masquerader

Treponema pallidum subsp. pallidum. Transmission: Sexual, congenital.

Stage	Clinical Features	Diagnosis
Primary	Painless chancre.	Dark-field microscopy
Secondary	Maculopapular rash (palms/soles), condylomata lata, mucous patches. > ⭐ The Jarisch-Herxheimer reaction, an acute febrile reaction often with headache and myalgias, can occur within hours after treatment initiation for syphilis, especially with penicillin.	Serology
Latent	Early/Late. Asymptomatic.	Serology
Tertiary	Gummas, Cardiovascular (aortitis), Neurosyphilis (tabes dorsalis, general paresis).	Serology, CSF VDRL

Congenital Syphilis: Hutchinson's triad (📌 Interstitial keratitis, Notched incisors, 8th nerve deafness).
Diagnosis Algorithm:
Serology:
- Non-treponemal (Screening/monitor): VDRL, RPR. 📌 VDRL False +ves: Viral, Drugs, Rheumatic fever, Lupus/Leprosy, Pregnancy.
- Treponemal (Confirmatory): FTA-ABS, TPPA, MHA-TP.
Treatment: Penicillin G (all stages). Jarisch-Herxheimer reaction.

Borrelia: Lyme & Relapsing Fever - Tick-Borne Terrors

Spirochetes transmitted by arthropods. Key differences:

Feature	Lyme Disease (B. burgdorferi)	Relapsing Fever (B. recurrentis, others)
Vector	Ixodes ticks (hard)	Louse (epidemic), Ornithodoros ticks (soft, endemic)
Key Clinical Features	Stage 1: Erythema migrans (EM, "bull's-eye").	Recurrent high fever, chills, headache.
	Stage 2: Neuro (Bell's palsy), Cardiac (AV block).	Due to antigenic variation (key feature).
	Stage 3: Arthritis, Encephalopathy.
Diagnosis	Serology (ELISA, Western Blot, two-tier)	Blood smear (Giemsa/Wright) during fever.
Treatment	Doxycycline, Amoxicillin, Ceftriaxone	Tetracycline, Penicillin.

📌 BAKE a Key Lyme pie: Bell's palsy, Arthritis, Karditis, Erythema migrans.

Erythema migrans rash

Leptospira: Leptospirosis - Weil's Wrath

Organism: Leptospira interrogans (thin, coiled spirochete with characteristic hooked ends).
Source: Zoonosis (rodents, domestic animals - urine).
Transmission: Contaminated water/soil, direct contact with infected animal tissues.
Clinical Syndromes:
- Anicteric Leptospirosis (90%): Biphasic, usually self-limited.
  - Septicemic phase: Fever, myalgia (esp. calves), headache, conjunctival suffusion.
  - Immune phase: Aseptic meningitis, uveitis.
- Icteric Leptospirosis / Weil's Disease (Severe, 5-10%): Characterized by jaundice, acute kidney injury (AKI), hemorrhage, and myocarditis.
  
  ⭐ Weil's disease, the severe form of leptospirosis, classically presents with a triad of jaundice, acute kidney injury, and hemorrhagic manifestations.
Diagnosis:
- Culture (Fletcher's medium): Blood/CSF (1st week), urine (after 1st week).
- Serology: MAT (Microscopic Agglutination Test) is gold standard.
- PCR: Useful for early diagnosis.
Treatment:
- Mild disease / Prophylaxis: Doxycycline.
- Severe disease: Penicillin G or Ceftriaxone (IV).

High‑Yield Points - ⚡ Biggest Takeaways

Spirochetes: Gram-negative, spiral-shaped bacteria with unique endoflagella for motility.

Treponema pallidum causes syphilis; visualized by dark-field microscopy, non-culturable on artificial media.

Borrelia burgdorferi causes Lyme disease (classic sign: erythema migrans), transmitted by Ixodes ticks.

Leptospira interrogans causes leptospirosis (severe form: Weil's disease), from animal urine-contaminated water.

Relapsing fever (Borrelia spp.) is characterized by recurrent fever due to antigenic variation.

Treatments include Penicillin / Doxycycline; beware Jarisch-Herxheimer reaction with therapy.

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Spirochetes