When treated for a bacterial infection, why may a hamster die following one or more injections of penicillin?

• A. Penicillin is not effective on gram-positive organisms.
• B. Overgrowth of gram-negative organisms may secrete a lethal toxin.
• C. Hamsters secrete an enzyme that changes penicillin to a toxic metabolite.
• D. The dose of penicillin given was probably too high.

Answer: (B)

Antibiotics can disrupt the normal gut bacteria, and hamsters are especially susceptible to this. When penicillin is given, it can wipe out a large portion of the protective flora in the intestine, allowing certain gram-negative organisms to overgrow. Many of these gram-negative bacteria can produce potent toxins, and the presence of these toxins can drive severe illness or death even as the infection being treated is addressed. This toxin-mediated enteric disruption is the key mechanism, rather than a failure of penicillin to work on bacteria or an overactive hamster metabolism turning penicillin into a harmful metabolite. Overgrowth of toxin-producing gram-negative bacteria is the most plausible explanation for death following penicillin treatment in hamsters.