Part 1 obgyn notes Sri Lanka
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    Microbiology
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    H.ducreyi

    H.ducreyi

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    ⭐ THE 20% THAT GIVES 80% OF MARKS

    (If you remember ONLY this, you can answer almost any exam question.)

    1. Organism: Haemophilus ducreyi, Gram-negative coccobacillus
    2. Disease: Chancroid (painful, ragged ulcers + tender nodes)
    3. Lesion: “Soft chancre” → PAINFUL, bleeds easily
    4. Lymph nodes: Painful unilateral buboes
    5. Microscopy line: “School of fish / railroad track” pattern
    6. Growth requirement: Needs X-factor (hemin), special media
    7. Diagnosis: Mainly clinical + PCR
    8. Treatment: Azithromycin 1 g (single dose) or Ceftriaxone 250 mg IM (single dose)
    9. Differentiation: Syphilis = painless, HSV = painful vesicles → ulcers
    10. Chancroid increases HIV transmission risk

    Memorize these → 80% marks secured.

    🔬 FULL MICROBIOLOGY – EASY EXPLANATION

    1. Organism Properties

    • Gram reaction: Gram-negative
    • Shape: Short coccobacillus (small rod-like)
    • Arrangement: Appears in “school of fish” or railroad track parallel chains → classic exam point
    • Motility: Non-motile
    • Spores: Non-sporing
    • Capsule: No capsule
    • Oxygen: Facultative anaerobe
    • Temperature preference: 33–35°C (cooler than body temp)
    • Growth needs:
      • Requires X-factor (hemin)
      • Grows on:
        • Chocolate agar
        • Nairobi agar (specialised)
      • Slow-growing, difficult to culture → reason why clinical diagnosis important

    💡 Memory:

    “H. ducreyi = High-maintenance diva → needs X-factor + special agar + cooler temperature.”

    2. Transmission

    • Primarily sexual transmission
    • Organism enters through micro-abrasions
    • Highly infectious (exposure → easy transmission)

    3. Pathogenesis – How It Causes Ulcers

    • Enters skin → infects epidermis + dermis
    • Produces a cytotoxin (hemolysin) → causes tissue necrosis
    • Leads to:
      • Painful ulcers
      • Suppuration
      • Lymph node inflammation (buboes)

    Mechanism of ulcer:

    1. Papule →
    2. Pustule →
    3. Ulceration with necrotic base →
    4. Ragged edges, bleeds easily

    4. Clinical Features

    🔥 A. Ulcer of Chancroid

    • PAINFUL
    • Soft, not indurated (vs syphilis = hard chancre)
    • Ragged, “dirty” base
    • Bleeds on contact
    • Multiple lesions possible

    🔥 B. Lymph Nodes (Buboes)

    • Usually one-sided (unilateral)
    • Painful, fluctuant
    • May rupture → discharge pus

    🔥 C. Systemic Symptoms

    • Fever uncommon
    • Pain mainly local

    🆚 DIFFERENTIATION FROM OTHER GENITAL ULCERS

    Most common exam table:

    Disease
    Pain?
    Ulcer type
    Lymph nodes
    Organism
    Test
    Chancroid
    Painful
    Ragged soft ulcer
    Painful buboes
    H. ducreyi
    PCR
    Syphilis
    Painless
    Hard chancre
    Painless nodes
    T. pallidum
    VDRL + TPHA
    HSV
    Painful
    Vesicles → ulcers
    Tender nodes
    HSV
    PCR, culture
    LGV (C. trachomatis L1–L3)
    Shallow, may be painless
    Small ulcer → buboes
    Large painful nodes
    Chlamydia
    NAAT

    📌 Key Remember:

    “Painful H.D., Painless T.P.”

    (H. ducreyi painful. Treponema pallidum painless.)

    5. Laboratory Diagnosis

    A. Direct microscopy

    • Gram stain from ulcer exudate:
      • Small Gram-negative rods in school-of-fish pattern
    • Sensitivity is low (30–50%)

    B. Culture

    • Difficult
    • Needs chocolate agar + hemin
    • Slow (48–72 hours)
    • Often negative

    C. PCR

    • Best diagnostic tool
    • Detects H. ducreyi DNA
    • High sensitivity and specificity

    D. Other tests

    • Rule out syphilis (VDRL/TPHA)
    • Rule out HSV (PCR)

    6. Treatment – VERY EXAM HIGH-YIELD

    First-line (single dose options):

    • Azithromycin 1 g PO single dose ✔
    • Ceftriaxone 250 mg IM single dose ✔

    Alternatives:

    • Ciprofloxacin 500 mg BD × 3 days
    • Erythromycin 500 mg QID × 7 days

    Nodes (buboes):

    • Aspiration preferred
    • Avoid incision (delayed healing)

    Important fact:

    • Chancroid increases susceptibility to HIV transmission 3–10 fold.

    🎯 THE REAL HIGH-YIELD SUMMARY (20% → 80% marks)

    1. H. ducreyi = Gram-negative coccobacillus
    2. Causes chancroid: painful soft ulcer + painful buboes
    3. Ulcer→ ragged, bleeds easily
    4. Microscopy → school-of-fish pattern
    5. Growth requires X-factor (hemin)
    6. Diagnosis = mainly clinical, confirm with PCR
    7. Treatment = Azithromycin or Ceftriaxone (single dose)
    8. Differentials: syphilis painless, HSV vesicular
    9. Enhances HIV transmission risk
    10. Painful ulcers = H. ducreyi & HSV (rest painless)