Bisected pearls appearance on culture medium is seen in -

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.