Normal flora can cause disease under which conditions?

Normal flora can cause disease under which conditions?

• A. The host's immune system is compromised.
• B. The bacteria colonize a new site in the body.
• C. The bacteria colonize a different host.
• D. All of the above.

Answer: (D)

Normal flora can become harmful when the body’s defenses or the environment change in ways that remove they keep them in check. When the immune system is compromised, these microbes can overgrow or invade tissues they normally wouldn’t, turning into opportunistic infections. If bacteria move to a site they don’t usually inhabit or into a sterile region of the body, they encounter less resistance and can establish infection, even though they’re part of the normal flora elsewhere in the body. When the same microbes are introduced into a different host, they may cause disease if the new host lacks the defenses or has conditions that favor infection. Because these situations all enable normal flora to transition from harmless residents to disease-causing agents, the correct choice is all of the above.

Normal flora can become harmful when the body’s defenses or the environment change in ways that remove they keep them in check. When the immune system is compromised, these microbes can overgrow or invade tissues they normally wouldn’t, turning into opportunistic infections. If bacteria move to a site they don’t usually inhabit or into a sterile region of the body, they encounter less resistance and can establish infection, even though they’re part of the normal flora elsewhere in the body. When the same microbes are introduced into a different host, they may cause disease if the new host lacks the defenses or has conditions that favor infection. Because these situations all enable normal flora to transition from harmless residents to disease-causing agents, the correct choice is all of the above.