What best describes antibiotic-resistant bacteria?

The description of antibiotic-resistant bacteria as those that undergo mutation to resist antibiotics and reproduce in greater numbers is accurate because it highlights the primary mechanism by which resistance develops. Bacteria can acquire genetic mutations that render certain antibiotics ineffective. These changes can occur through various processes, including natural selection, horizontal gene transfer, or chromosomal mutations.

When exposure to antibiotics occurs, susceptible bacteria are killed off, while those with resistance mutations survive and continue to reproduce. This leads to a population of bacteria that is increasingly resistant to the antibiotic treatment, thus making infections harder to treat. Over time, these resistant strains can proliferate, leading to a significant public health concern, as they can contribute to more severe and difficult-to-treat infections.

The other options do not accurately characterize antibiotic-resistant bacteria. For instance, the notion that bacteria could be immune to all antibiotics oversimplifies the complexity of bacterial resistance. Additionally, suggesting that they are harmless to humans and animals does not recognize the fact that many antibiotic-resistant bacteria are pathogenic and can cause serious infections. Lastly, stating that they only exist in sterile environments misrepresents how and where antibiotic-resistant bacteria can be found, as they often thrive in various environments, including those that are not sterile.