Antibiotics and the Evolution of Antibiotic Resistance

Abstract

Antibiotics were introduced for human therapy few decades ago and their utilization has produced the rapid evolution of bacterial pathogens towards resistance. Before this recent and fast evolution, antibiotics and their resistance genes have evolved for millions of years in environmental microorganisms. Recent results suggest that, besides serving for inhibiting the growth of competitors, antibiotics might be signalling molecules in natural ecosystems and that some metabolic enzymes and signal-trafficking efflux pumps might render a phenotype of resistance in the presence of high concentrations of antibiotics. Antibiotic resistance can be developed by mutation or by the acquisition of resistance determinants by means of horizontal gene transfer. Spread of resistance is achieved through the combination of different elements, from resistance genes to plasmids and bacterial clones. The release of high amounts of antibiotics and resistance genes in natural habitats is challenging the microbial populations present in these ecosystems. Key concepts Key concepts * Some antibiotics can be involved in intermicrobial communication at the low concentrations likely found in most natural ecosystems. * The origin, spread and diversification of mechanisms of antibiotic resistance is an excellent model for studying real-time evolution. * The fact that a given gene confers resistance when transferred to a bacterial human pathogen does not necessarily mean that it plays the same functional role in its original host. * Exaptation is an evolutionary process by which a given determinant changes its function, without changing its structure, as the consequence of an environmental change. * Anthropogenic antibiotic pollution in the environment might modify the genetic structure of bacterial populations and communities. * Antibiotic resistance evolves frequently in a modular fashion, combining sequences, genes, genetic platforms and genetic vehicles. * The association of several antibiotic resistance genes in the same genetic vehicle favours their dissemination and persistence. * The spread of antibiotic resistance frequently occurs by the global dissemination of particularly transmissible bacterial resistant clones. * Antibiotic resistance is fixed in human or animal populations when the resistance genes enter into endemic clones. * Prediction of evolutionary trajectories should constitute the ultimate way to demonstrate the truth of hypothesis in evolutionary sciences.