Commensal bacteria can influence pathogen colonization through competitive exclusion.

Commensal bacteria can influence pathogen colonization through competitive exclusion.

• A. False
• B. Partially true
• C. Not relevant to host defense
• D. True

Answer: (D)

The concept being tested is colonization resistance provided by the normal gut microbiota through competitive exclusion. Commensal bacteria help keep pathogens at bay by occupying adhesion sites on the mucosa and consuming available nutrients, leaving fewer resources for invading microbes. They also create an environment that’s harder for pathogens to colonize—through production of antimicrobial compounds and metabolic byproducts that influence pH and other conditions—and they help train and balance the host immune response to detect and respond to invaders. Because of these actions, commensals can significantly influence how well a pathogen can establish itself, which is the essence of competitive exclusion as a defense mechanism. Disruption of the commensal community (for example, by antibiotics) often increases susceptibility to pathogen overgrowth, illustrating this protective role. So the statement is true.

The concept being tested is colonization resistance provided by the normal gut microbiota through competitive exclusion. Commensal bacteria help keep pathogens at bay by occupying adhesion sites on the mucosa and consuming available nutrients, leaving fewer resources for invading microbes. They also create an environment that’s harder for pathogens to colonize—through production of antimicrobial compounds and metabolic byproducts that influence pH and other conditions—and they help train and balance the host immune response to detect and respond to invaders. Because of these actions, commensals can significantly influence how well a pathogen can establish itself, which is the essence of competitive exclusion as a defense mechanism. Disruption of the commensal community (for example, by antibiotics) often increases susceptibility to pathogen overgrowth, illustrating this protective role. So the statement is true.