Bacterial Infections · Pathology

The 'Medusa head' appearance of colonies on blood agar is a characteristic culture finding for which bacterium?

  1. Clostridium tetani
  2. Bacillus anthracis
  3. Proteus mirabilis
  4. Pseudomonas aeruginosa
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Correct answer: Bacillus anthracis

Bacillus anthracis colonies are non-hemolytic, grey-white, and have a dry, 'ground glass' appearance. Under low-power magnification, the edges of the colony show long, wavy chains of bacilli resembling a 'Medusa head'.

Difficulty: Medium Question 20 of 20

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