What is an opportunistic pathogen?

An opportunistic pathogen is defined as a microorganism that typically does not cause disease in a healthy individual with a fully functioning immune system but can lead to illness when the host's defenses are weakened or compromised. This may occur due to various factors such as immunosuppressive conditions, age, malnutrition, or certain medical treatments, like chemotherapy.

For instance, common opportunistic pathogens include certain strains of bacteria, fungi, and viruses that can exploit vulnerabilities in the host's immune response. In patients with weakened immune systems, these organisms can invade tissues, leading to infections that would not normally occur in individuals with intact immune function.

The other options do not accurately capture the essence of opportunistic pathogens. A microorganism that causes disease when host defenses are strong contradicts the definition of opportunistic pathogens, as they thrive when defenses are low, not strong. A microorganism that exclusively causes skin infections suggests a specificity that does not encompass the broader impact of opportunistic pathogens, which can infect various body systems. Finally, a harmless microorganism that aids in digestion describes commensals or beneficial microbes and does not relate to the pathogenic characteristics of opportunistic pathogens.