<prompt> Bisected pearls appearance on culture medium is seen in -BrucellaBordetellaHaemophilus ducreyiPseudomonas  <response>: 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 Laceys 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 stuarts medium and Mischuloss charcol agar. 