Which of the following is NOT a role of the normal microbiota?

The correct answer highlights that causing infections is not a role of the normal microbiota. The normal microbiota, which consists of various microorganisms residing in and on the human body, generally performs beneficial functions that contribute to overall health. Its primary roles include supporting immune function by training the immune system to recognize harmful pathogens, producing essential vitamins such as vitamin K and some B vitamins, and preventing the colonization of pathogens by occupying niches and utilizing available nutrients, thereby making it more challenging for harmful microorganisms to establish infection.

While it is true that disruptions in the normal microbiota can lead to opportunistic infections under certain conditions, the normal microbiota itself serves mainly to protect the host and maintain a balanced environment. Thus, the characteristic that would stand out as not aligned with the normal functions of healthy microbiota is the act of causing infections, which indicates a pathogenic potential rather than a beneficial role.