Final answer:
The difference between a microbe that is part of the microbiome and a pathogen is that microbiome microbes are typically harmless and can be beneficial, while pathogens are disease-causing agents that can infect and harm the host.
Step-by-step explanation:
According to the germ theory of disease, infectious disease is caused by infection of pathogens, commonly known as germs. However, not all microbes are harmful. Humans host complex microbiomes composed of various microbes that live symbiotically within our bodies, providing benefits like digestion aid and protection against harmful pathogens through microbial antagonism. So, what differentiates a microbiome constituent from a pathogen?
A microbe that is part of the microbiome is typically harmless and may even provide beneficial functions to the host. These microbes can outcompete potential pathogens, preventing them from establishing an infection. In contrast, a pathogen is a type of microbe that can cause disease when it infects a host organism. Pathogens such as bacteria, viruses, fungi, and protozoa can spread from one host to another, possibly resulting in contagious diseases like the common cold, influenza, and malaria.