What are opportunistic pathogens?

Opportunistic pathogens are microorganisms that typically do not cause disease in healthy individuals with functioning immune systems but can lead to infections in certain circumstances, particularly in immunocompromised individuals. This can include individuals with weakened immune systems due to conditions such as HIV/AIDS, cancer treatments, or the use of immunosuppressive drugs. In these cases, opportunistic pathogens can take advantage of the host's weakened defenses, leading to infections that could be severe or even life-threatening.

The first choice refers to the normal microbiota that coexist with healthy hosts without causing harm under normal circumstances, which does not capture the essence of opportunism. The third choice incorrectly implies that all pathogens have a consistent ability to harm, while opportunistic pathogens are characterized by their reliance on specific conditions within the host. The fourth choice discusses microbes that enhance immunity, which is unrelated to the definition of opportunistic pathogens, as these microbes can actually lead to disease rather than enhancing health.