What is an infection defined as in pathogenic microbiology?

An infection in pathogenic microbiology is correctly defined as the invasion and multiplication of pathogens in the body, leading to tissue damage. This definition encompasses the key aspects of infection: not only does it involve the entry of pathogens into the host, but it also highlights their ability to grow and proliferate within the host tissues. The consequence of this invasion often results in tissue damage, which can manifest as disease symptoms.

This definition is important because it distinguishes between mere presence of pathogens and their active role in causing harm. While pathogens may be present without causing symptoms, this does not classify as an infection. Similarly, the notion that infection is solely about the rapid multiplication of bacteria is overly restrictive, as infections can also involve viruses, fungi, and parasites. Thus, the best characterization of an infection incorporates both the invasion and the subsequent pathological effects on the host.