This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Bacteria, Subject name: Microbiology
[{'content': 'Bisected pearls appearance on culture medium is seen in - \nSelect and explain. \nA. Brucella, B. Bordetella, C. Haemophilus ducreyi, D. Pseudomonas', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Ans. is \'b\' i.e., Bordetella * Bordetella are gram-negative, capsulated, fimbriated, nonmotile coccobacillus.* They show bipolar metachromatic granules on staining with toluidine blue.* They are strict aerobes.* They are biologically inactive (non-fermenters).* There catalase and oxidase are positive.* There are two important members in this genusi) B. pertussis: Causative agent of whooping cough (pertussis).ii) B. parapertussis: Causes milder form of whooping cough.* There is no cross immunity between B. pertussis and B. parapertussis.Culture* Bordet-Gengou glycerine potato-blood agar medium is commonly used.* Incorporation of diamidine fluoride and penicillin (Lacey\'s DFP medium) makes it more selective.* It produces bisected pearls or mercury drops colonies.* Confluent growth is present with "aluminium paint" appearance.* In culture smears, the bacilli are arranged in loose clumps with clear spaces in between giving a thumb print appearance.* Transport media used are modified stuart\'s medium and Mischulos\'s charcol agar.', 'role': 'assistant'}]