Bordetella pertussis

A 3-month-old female infant from rural Madhya Pradesh presents with a 2-week history of paroxysmal cough, followed by an inspiratory 'whoop' sound. The mother reports the child was completely well until 2 weeks ago. On examination, the infant appears malnourished, with conjunctival petechiae and subconjunctival hemorrhages. Chest examination reveals scattered crackles. The child has not received any vaccinations. A nasopharyngeal swab is sent for culture on Bordet–Gengou medium. Which of the following best explains the pathophysiology of the characteristic 'whooping' cough in this patient?

Which toxin produced by Bordetella pertussis is responsible for the characteristic paroxysmal cough and is encoded by a chromosomal gene regulated by the BvgAS two-component system?

A 6-month-old male infant from Delhi presents with a 3-week history of paroxysmal cough with post-tussive vomiting and episodes of apnea. The child had received only one dose of pentavalent vaccine (DPT–HepB–Hib) at 6 weeks of age. On examination, the infant is tachypneic (respiratory rate 60/min) with mild cyanosis during coughing episodes. Laboratory investigations show WBC 25,000/μL with 85% lymphocytes (absolute lymphocyte count 21,250/μL). A nasopharyngeal aspirate is sent for culture and PCR. Which of the following is the single most important factor that explains the severe disease manifestation and high mortality risk in this patient?

Bordetella pertussis is isolated from a respiratory specimen and shows a characteristic gram-negative coccobacillus morphology. Which selective medium is most appropriate for primary isolation of this organism?