A 6-month-old infant presents with cough and fever; Regan-Lowe agar shows small, smooth, glistening colonies after 5 days; Bordet-Gengou agar shows similar colonies; BAP shows no growth; Oxidase is negative; Motility is non-motile. Which organism is suspected?

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Multiple Choice

A 6-month-old infant presents with cough and fever; Regan-Lowe agar shows small, smooth, glistening colonies after 5 days; Bordet-Gengou agar shows similar colonies; BAP shows no growth; Oxidase is negative; Motility is non-motile. Which organism is suspected?

The main idea here is recognizing Bordetella pertussis from its characteristic culture pattern on selective pertussis media and the clinical context. Regan-Lowe agar and Bordet-Gengou agar are specifically used to grow B. pertussis; Regan-Lowe contains antibiotics to suppress contaminating flora, while Bordet-Gengou is a potato-based medium that supports pertussis growth. Seeing small, smooth, glistening colonies after several days on both media strongly points to B. pertussis, especially since blood agar shows no growth because this organism is fastidious and does not grow well on routine media. The organism being non-motile fits Bordetella species, which helps distinguish it from other Gram-negative rods that might be motile. The age and presentation—a 6-month-old infant with cough—fit pertussis, where culture remains a key diagnostic clue in the right clinical setting. Haemophilus influenzae would typically require X and V factors and would not yield the same growth on these pertussis-specific media. Legionella pneumophila grows best on specialized media like BCYE, not on Regan-Lowe or Bordet-Gengou, and Bordetella bronchiseptica is usually motile and associated with animal infections rather than classic infant pertussis. So, the combination of selective culture growth on Regan-Lowe and Bordet-Gengou, lack of growth on routine blood agar, non-motility, and the infant with cough points to Bordetella pertussis.

The main idea here is recognizing Bordetella pertussis from its characteristic culture pattern on selective pertussis media and the clinical context. Regan-Lowe agar and Bordet-Gengou agar are specifically used to grow B. pertussis; Regan-Lowe contains antibiotics to suppress contaminating flora, while Bordet-Gengou is a potato-based medium that supports pertussis growth. Seeing small, smooth, glistening colonies after several days on both media strongly points to B. pertussis, especially since blood agar shows no growth because this organism is fastidious and does not grow well on routine media.

The organism being non-motile fits Bordetella species, which helps distinguish it from other Gram-negative rods that might be motile. The age and presentation—a 6-month-old infant with cough—fit pertussis, where culture remains a key diagnostic clue in the right clinical setting. Haemophilus influenzae would typically require X and V factors and would not yield the same growth on these pertussis-specific media. Legionella pneumophila grows best on specialized media like BCYE, not on Regan-Lowe or Bordet-Gengou, and Bordetella bronchiseptica is usually motile and associated with animal infections rather than classic infant pertussis.

So, the combination of selective culture growth on Regan-Lowe and Bordet-Gengou, lack of growth on routine blood agar, non-motility, and the infant with cough points to Bordetella pertussis.

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