ANTIBIOTIC-SELECTIVE ENVIRONMENTS

The evolution and spread of antibiotic resistance depends on che antib iotic pressure exerted in the microbial environment. Selective effects occur in selective compartments, where particular antibiotic concentr ations result in a differential growth rate of resistant bacterial var iants. This may happen even at very low antibiotic concentrations able to select low-level-resistant bacteria. When more than one antibiotic is present in the environment, the multiple and fluctuating pressure produces the selection of bacterial variants that use multiple or mult ipurpose mechanisms or optimize a single mechanism of resistance to su rvive under the variable environmental conditions, Host factors such a s immunity contribute to the selective process, Antibiotics themselves may promote bacterial diversity, either mediated by the random drift effect or triggering the increase of mutational events under bacterial stress. Analysis of selective environment-related antibiotic-host-bac teria interactions is essential to understanding the biology of antibi otic resistance.