In vitro generation of Salmonella spp. mutants following repeated exposure to beta-lactam antibiotics.

Beta-lactams are a group of drugs considered to be the treatment of choice in cases of salmonellosis, although many isolates that are clinically resistant to these compounds have been reported. We developed an in vitro model to determine the dynamics of the generation of resistant mutants following repeated exposure to these drugs. All the isolates exposed repeatedly to amoxicillin and cefotaxime exhibit a decrease in their susceptibility to these compounds and to many other beta-lactam drugs. However, in many cases this reduction in susceptibility is not detected if the CLSI criteria are applied. These mutants with reduced susceptibility may be the reason for therapeutic failures, so this phenomenon should be studied in greater detail by means of in vitro models or clinical studies.