This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Systemic Bacteriology (Haemophilus, Yersinia, Spirochaetes, Ricketssia, Chlamydia, Mycoplasma and Miscellaneous Bacteria), Subject name: Microbiology
[{'content': "'School of fish' appearance under microscope is seen in: \nSelect and explain. \nA. Cholera, B. Chancroid, C. Syphilis, D. Diphtheria", 'role': 'user'}, {'content': 'Answer: B \nExplanation: 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.', 'role': 'assistant'}]