Ans. a (H. ducreyi). (Ref. Harrison, Principles of Internal Medicine 18th ed., / Chap. 130 and Chapter 145.)HAEMOPHILUS DUCREYI# H. ducreyi is etiologic agent of chancroid, a STD characterized by genital ulceration and inguinal adenitis. It is a highly fastidious coccobacillary gram-negative bacterium whose growth requires X factor (hemin).# After an incubation period of 4-7 days, the initial lesion a papule with surrounding erythema appears. In 2-3 days, the papule evolves into a pustule, which spontaneously ruptures and forms a sharply circumscribed ulcer that is generally not indurated. The ulcers are painful and bleed easily with little or no inflammation in vicinity. Some develop enlarged, tender inguinal LNs. Multiple ulcers can coalesce to form giant ulcer.# Treatment: include: (1) a single 1-g oral dose of azithromycin; (2) ceftriaxone (250 mg IM in a single dose); (3) ciprofloxacin (500 mg oral BD for 3 days); and (4) erythromycin base (500 mg oral tid for 7 days).STDsS.NoSTDCausative agentDiagnosisTreatment1.Chancroid (soft sore)H. ducreyi"School of fish"/Rail road trackCotrimoxazole& Erythromycin2.LGVChlamydiaHP bodies (Giemsa stain)Tetracycline3.Syphilis (hard chancre)T. pallidumDarkground microscopyPenicillin4.Genital herpesH. simplex 2-Acyclovir5.Donovaniasis (granuloma inguinale)Leish mania donovani-Erythromycin6.GonorrhoeaN. gonorrhoea-Penicillin &Ceftriaxone7.TrichomoniasisT. vaginalisStrawberry vaginaMetro/tinidazole