H. ducreyi
Summary
Haemophilus ducreyi is a gram-negative coccobacillus that causes chancroid, a sexually transmitted infection producing painful genital ulcers with painful suppurative inguinal lymphadenopathy. The mnemonic is that you 'do cry' with ducreyi.
Detail
H. ducreyi is fastidious and difficult to culture, requiring enriched media, and on Gram stain arranged bacilli give a 'school of fish' or 'railroad track' appearance. The ulcer of chancroid is soft, deep, ragged, and exquisitely tender with a purulent grey base and undermined edges, and unilateral tender fluctuant inguinal buboes develop in about half of cases and may need aspiration. This picture contrasts sharply with the chancre of primary syphilis, which is single, indurated, clean-based, and painless with non-tender lymphadenopathy, and with lymphogranuloma venereum from Chlamydia trachomatis L1-L3, in which a transient painless ulcer is followed by prominent painful lymphadenopathy and the groove sign. Herpes simplex causes multiple shallow painful vesicles and ulcers with tender adenopathy but is usually preceded by vesicles. Diagnosis of chancroid is clinical after excluding syphilis and herpes; treatment is a single dose of azithromycin or ceftriaxone, or erythromycin or ciprofloxacin.
Sources
- Levinson Medical Microbiology and Immunology
- First Aid for the USMLE Step 1
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