Bacteriology: Practice Question

A six year old female patient presents with a paroxysmal cough accompanied by an inspiratory whoop. X-ray reveals a right fifth rib fracture. The suspected infectious agent should be cultured on which of the following plates?
  1. Regan-Lowe agar
  2. Martin-Lewis agar
  3. Thayer-martin agar
  4. MacConkey agar
  5. TCBS agar
Show Answer and Explanations

Regan-Lowe agar — Correct answer

Correct. Regan-Lowe agar is selective for Bordetella pertussis, a Gram negative coccobacillus that causes whooping cough. Pertussis toxin inhibits G proteins rendering them inactive and unable to inhibit adenylate cyclase, resulting in excess cAMP and disruption of normal cell signalling. Regan-Lowe agar is also used to plate B. parapertussis, which causes a less severe form of whooping cough.

Martin-Lewis agar

Incorrect. Martin-Lewis and Thayer-Martin agars are used to select Neisseria gonorrhoeae and Neisseria meningitidis.

Thayer-martin agar

Incorrect. Thayer-Martin agar and Martin-Lewis agar are used for the selection of Neisseria gonorrhoeae and Neisseria meningitidis.

MacConkey agar

Incorrect. MacConkey agar is selective and differential for Gram negatives.

TCBS agar

Incorrect. TCBS agar is used for stool culture - it is selective and differential for Vibrio spp.

Summary

Summary: Regan-Lowe agar is selective for B. pertussis and B. parapertussis. Pertussis toxin inhibits G proteins, relieving the inhibition of adenylate cyclase, causing excess cAMP.
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