Which of the following statements is not true of clostridia?

• A. Pseudomembranous colitis is due to a toxin produced by C. difficile.
• B. Clinically significant clostridia are found in the normal flora of the colon and in the soil.
• C. Botulism is caused by ingesting preformed toxin and can be prevented by boiling food prior to eating.
• D. C. tetani spores will form in the presence of oxygen; therefore, anaerobiosis in a wound is not required to cause tetanus.

Answer: (D)

Clostridia are obligate anaerobes that form spores and produce potent toxins. Infections typically arise when a wound or environment becomes low in oxygen, allowing the spores to germinate and the bacteria to multiply and release toxin. That’s why oxygen presence in a wound would hinder the germination and toxin production that lead to tetanus. The statement claiming spores form in the presence of oxygen is not true because the germination and toxin-making step require a low-oxygen environment; oxygen actually inhibits that process, making anaerobiosis in a wound a key factor for tetanus to develop.

Pseudomembranous colitis is caused by toxins A and B from C. difficile, which disrupt the colonic mucosa—this is a well-established toxin-mediated effect. Clostridia that are clinically significant are indeed found both in the normal colon flora and in soil, reflecting their environmental and gut presence. Botulism stems from ingestion of preformed toxin in contaminated food, and since the toxin is heat-labile, boiling the food prior to eating can inactivate the toxin and help prevent illness.