How can microbial drug resistance be introduced into a population?

Microbial drug resistance can indeed be introduced into a population through the introduction of new genes. This process often occurs via horizontal gene transfer, where genetic material is exchanged among bacteria. For instance, resistant bacteria can share plasmids, which are small, circular pieces of DNA that often carry genes for antibiotic resistance. This genetic exchange allows sensitive bacteria to acquire resistance traits from resistant strains, effectively spreading drug resistance within a population.

While mutations can also lead to resistance, as they result from changes in the existing DNA of organisms, horizontal gene transfer is a more direct method for spreading resistance across different bacterial strains. Exposure to antibiotics can select for already resistant strains rather than introducing new resistance, and environmental changes may influence the survival of certain strains but do not directly introduce resistance genes. Therefore, the introduction of new genes is a critical mechanism for developing and propagating drug resistance in microbial populations.