How does unnecessary antibiotic use contribute to drug-resistant bacteria?

Unnecessary or indiscriminate antibiotic use contributes to the development of drug-resistant bacteria by acting as a powerful selective pressure on bacterial populations.123

When antibiotics are used, they typically kill or inhibit the growth of vulnerable bacteria. However, if a few bacteria in the population possess genetic traits that make them less susceptible to the drug, they survive. With their vulnerable competitors removed, these resistant strains are free to proliferate and dominate the population.123

Furthermore, bacteria can acquire resistance through the exchange of genetic material, such as plasmids, which often carry genes that encode enzymes capable of inactivating antibiotics. The widespread and improper use of these drugs—including their prophylactic use in intensive animal farming—accelerates this process by constantly exposing bacteria to sub-lethal levels of antibiotics, favoring the survival and replication of resistant organisms. This creates a significant public health challenge, as infections caused by these resistant strains can become difficult or impossible to treat with standard medical therapies.2341