Name a common opportunistic pathogen found in immunocompromised individuals.

Candida albicans is a well-known opportunistic pathogen that frequently affects immunocompromised individuals due to its capacity to exploit weakened immune defenses. In healthy individuals, Candida albicans is typically a harmless part of the normal microbiota, residing in areas such as the mouth, gut, and vagina. However, in cases where the immune system is compromised—whether due to conditions like HIV/AIDS, cancer treatments, or prolonged antibiotic use—this yeast can overgrow and lead to various infections. These can range from superficial infections like thrush or vaginal yeast infections to more severe systemic infections, especially in patients with severely weakened immune systems.

The other options could potentially cause infections in immunocompromised individuals, but they are not classified as common opportunistic pathogens in the same way that Candida is. For example, Streptococcus pneumoniae is primarily associated with infections in healthy individuals, particularly pneumonia, and is more prevalent in certain circumstances rather than being opportunistic. Escherichia coli generally causes infections in specific conditions rather than routinely presenting a risk in immunocompromised hosts. Clostridium difficile is more associated with antibiotic-associated diarrhea and colitis, particularly in hospitalized patients but again is not primarily viewed as an opportunistic pathogen like Candida albicans.