A phenotypic study of the resistome in a peri-urban ecosystem.

Since the discovery of antibiotics, the dispersion of resistance genes has increased exponentially, leading to the current state in which it has become increasingly difficult to achieve an effective treatment for infectious diseases. The enormous capacity for genetic exchange between microorganisms is causing resistance genes to be able to reach all environments, even those where there is no anthropogenic impact or exposure to these drugs. In this work, a phenotypic study of the resistome has been conducted in a peri-urban ecosystem (Granada, Spain), wherein the resistance to 32 antibiotics of 710 bacterial strains isolated from 70 samples from different ecological niches with varying levels of exposure to antibiotics and anthropic action has been determined. The study of resistances using phenotypic procedures constitutes a very useful and complementary alternative to genomic methods. The obtained results show a high percentage of resistance in all the subsystems analysed, stating high multi-resistance profiles. Vancomycin and erythromycin were the antibiotics to which the highest levels of resistance were observed, whereas the lowest levels were obtained in chloramphenicol. Regarding the environments studied, the highest percentages of resistance were found in wastewater, farms and food. It should be noted that in natural soil samples (not exposed to antibiotics or anthropogenic activities), worrying levels of resistance to practically all the groups of antibiotics analysed were detected. These results support the generally accepted conclusion that an appropriate control and management of wastewater and solid waste that may contain antibiotics or resistant bacteria is really important to prevent the wide propagation of the resistome in the environment.