What is a pathogen?

A pathogen is defined as a microbe that is harmful and has the potential to cause infection or disease in a host. This includes a variety of microorganisms such as bacteria, viruses, fungi, and parasites that can invade the body, multiply, and disrupt normal bodily functions. The harmful effects of pathogens can lead to illnesses ranging from mild infections to severe diseases, highlighting their role as agents of disease.

In contrast, the other options describe microbes that do not pose a threat to health—harmless microbes in the body can be part of the normal flora and contribute to overall health, microbes that aid digestion are beneficial for breaking down food and nutrient absorption, and friendly bacteria found in water also do not cause harm. Understanding what constitutes a pathogen is crucial for preventing infections and maintaining health.