In the context of infectious disease, what is a pathogen?

• A. A commensal organism that normally benefits the host and does not cause disease
• B. A host defense molecule that neutralizes microbes by binding to antigens
• C. A microorganism or other infectious agent that can cause disease in a host
• D. Any nonliving chemical toxin that causes illness without involving an infectious agent

Answer: (C)

Verified step by step guidance

1. Step 1: Understand the term 'pathogen' in microbiology. A pathogen is an agent that causes disease in a host organism.
2. Step 2: Review the options given and identify which describes an organism or agent capable of causing disease.
3. Step 3: Recognize that a commensal organism benefits the host and does not cause disease, so it is not a pathogen.
4. Step 4: Note that a host defense molecule neutralizing microbes is part of the immune response, not a pathogen itself.
5. Step 5: Identify that a nonliving chemical toxin causing illness without an infectious agent is not classified as a pathogen, since pathogens are infectious agents.