<prompt> School of fish appearance under microscope is seen in:CholeraChancroidSyphilisDiphtheria  <response>: The causative agent of chancroid soft sore is H. ducreyi. When examined by Gram stain, organisms from culture often clump in long parallel strands, producing a so-called school of fish or railroad track appearance. This morphology can occasionally be seen in Gram-stained smears from clinical specimens Chancroid is a genital ulcerative disease GUD and sexually transmitted infection characterized by soft nonindurated ulcers with irregular borders and tender inguinal lymphadenopathy, or buboes. The specimen of choice for the diagnosis is a swab that has been taken from the base of the genital ulcer. Culture is considered the gold standard. H ducreyi can grow well on a chocolate Agar supplemented with 1 Iso VitaleX and 5 sheep blood or fetal calf serum. High levels of carbon dioxide are preferred. However, nucleic acid amplification methods are more sensitive. 