What is an opportunistic pathogen?

An opportunistic pathogen is defined as a microorganism that does not typically cause disease in a healthy individual but can lead to an infection when the host's immune system is compromised or when the microorganism gains access to a part of the body that it normally does not inhabit. This concept is crucial in understanding how certain pathogens can exploit specific conditions to cause disease, such as when a person is immunocompromised due to conditions like HIV, cancer treatments, or antibiotic use, which disrupts normal flora.

In contrast, a microorganism that always causes disease represents strong pathogenicity, indicating it can infect healthy individuals without any immunocompromised status. This differentiates it from opportunistic pathogens, which rely on specific circumstances to cause disease. Similarly, microorganisms that only live in specific conditions or are harmless do not fit the definition of opportunistic pathogens, as they either require specific environments to live or do not pose any threat to host health under normal conditions. Understanding this classification is key in microbiology, especially in clinical contexts where the risk of opportunistic infections is a significant concern.