The agent that causes an infection and disease is most commonly referred to as the ______ agent.

• A. pathogenic
• B. opportunistic
• C. commensal
• D. saprophytic

Answer: (A)

Verified step by step guidance

1. Understand the key terms related to microbial agents: 'pathogenic', 'opportunistic', 'commensal', and 'saprophytic'.
2. 'Pathogenic' refers to microorganisms that cause disease in a host.
3. 'Opportunistic' agents cause disease primarily when the host's immune system is compromised.
4. 'Commensal' organisms live on or within a host without causing harm.
5. 'Saprophytic' organisms obtain nutrients from dead or decaying organic matter and typically do not cause disease.
6. Since the question asks for the agent that causes infection and disease most commonly, identify 'pathogenic' as the correct term.