REF: (B) B. pertussisREF: Jawetz Microbiology, 24th Ed Ch. 19BORDETELLA PERTUSSIS:The organisms are minute gram-negative coccobacilli resembling H influenzae. With toluidine blue stain, bipolar metachromatic granules can be demonstrated. A capsule is present. After an incubation period of about 2 weeks, the "catarrhal stage" develops, with mild coughing and sneezing. During this stage, large numbers of organisms are sprayed in droplets, and the patient is highly infectious but not very ill. During the "paroxysmal" stage, the cough develops its explosive character and the characteristic "whoop" upon inhalation. This leads to rapid exhaustion and may be associated with vomiting, cyanosis, and convulsions. The "whoop" and major complications occur predominantly in infants; paroxysmal coughing predominates in older children and adults. The white blood count is high (16,000-30,000/ uL), with an absolute lymphocytosis. Among provided options, T. pestis and B. pertussis produce bipolar metachromatic appearance, but considering the partial immunization status and age of patient, b. pertussis is answer of choice.