A Level Biology Practice Exam 2025 - Free A Level Biology Practice Questions and Study Guide

Clostridium difficile, often referred to as C. diff, is indeed a species of Gram-positive bacteria. It is known for its role in antibiotic-associated diarrhea and can cause more severe gastrointestinal conditions, such as colitis. One of the key features of C. difficile is its resistance to many antibiotics, which is mainly due to the production of spores that can survive harsh conditions and allow the bacterium to persist even in environments where antibiotics are present. This resistance makes it difficult to treat infections effectively, leading to recurrent episodes in individuals who have been treated previously.

The other options do not accurately characterize C. difficile. For instance, it is not Gram-negative, nor does it aid digestion; instead, it disrupts the normal gut flora. It is not a virus, and it does not primarily affect respiratory health, as its primary impact is on the gastrointestinal system. Therefore, the description of C. difficile as a Gram-positive bacterium that is resistant to most antibiotics accurately conveys its significant characteristics and pathogenic effects.