Microbiology Practice Exam 2026 - Free Microbiology Practice Questions and Study Guide

Antibiotics primarily target bacteria, leading to a reduction in their populations, which can disrupt the natural balance of the microbiome. The microbiome consists of a diverse array of microorganisms, including beneficial bacteria that play essential roles in digestion, metabolism, and immune system function. When antibiotics are administered, they do not distinguish between pathogenic bacteria and beneficial bacteria, which can result in an unintended decrease in the diversity and abundance of these helpful microbes. This disruption can lead to conditions such as dysbiosis, where harmful bacteria may proliferate in the absence of their competitors, and can also give rise to opportunistic infections, such as Clostridium difficile.

The other options are less accurate as they either exaggerate or misrepresent the effect of antibiotics on microbial populations. They do not enhance growth universally, nor do they have a neutral impact; rather, they significantly alter the microbial landscape. Additionally, while antibiotics can influence immune responses indirectly through modifications of the microbiome, this is not their primary action.