Occurrence of ESBL-producing Escherichia coli in soils subjected to livestock grazing in Azores archipelago: an environment-health pollution issue?

Antibiotics are successful drugs used in human and animal therapy; however, they must be considered as environmental pollutants. This study aims to isolate and characterize the extended-spectrum β-lactamase (ESBL) producing Escherichia coli soil from Azores Archipelago subjected to livestock agricultural practices. Twenty-four soil samples were collected from three different pasture systems with different number of cattle heads, and from a control site. Antibiotic susceptibility method was performed by Kirby-Bauer disk diffusion method against 16 antibiotics, and the presence of genes encoding lactamases, antimicrobial resistance genes, virulence factors, and phylogenetic groups was determined by polymerase chain reaction (PCR). Nine ESBLs were recovered from the three grazing sites, and all isolates presented the beta-lactamase genes blaCTX-M-3 and blaSHV. E. coli isolates were resistance to tetracycline and streptomycin and harbored the tetB, strA, and strB genes. One isolate also showed resistance to sulfonamides, and the genes sul1 and sul2 were detected. The isolates were grouped into the following phylogenic groups: B1 (n = 6), D (n = 2), and A (n = 1). The presence of antibiotics and resistance genes in soils may be the source to the development of antimicrobial resistance, which may have negative consequences in human and animal health.