Gilthead seabream (Sparus aurata) as carriers of SHV-12 and TEM-52 extended-spectrum beta-lactamases-containing Escherichia coli isolates.

In recent years, bacterial resistance to beta-lactam antibiotics has risen dramatically in Escherichia coli isolated from animals that could pass through the food chain to humans. One hundred eighteen fecal samples of Sparus aurata were tested for extended-spectrum beta-lactamase (ESBL)-containing E. coli recovery. Susceptibility to 16 antimicrobial agents was performed by disk diffusion. ESBL-phenotypic detection was carried out by double-disk test, and the presence of genes encoding TEM, OXA, SHV, and CTX-M type beta-lactamases was studied by polymerase chain reaction and sequencing. The detection of other antimicrobial resistance mechanisms and phylogenetic groups was also performed in recovered isolates as well as their clonal diversity by pulsed-field gel electrophoresis. Five of the 118 fecal samples harbored ESBL-positive E. coli isolates (4.2%), and one isolate per sample was completely characterized. These five ESBL-positive E. coli isolates contained the bla(TEM-52) or bla(SHV-12) genes, as well as a variety of other resistance genes (cmlA, tetA, aadA, sul1, sul2, and sul3). Four isolates harbored class 1 integrons with the following gene cassettes in their variable region: dfrA1 + aadA1 (one isolate) and sat + psp + aadA2 (three isolates). Four unrelated pulsed-field gel electrophoresis patterns were identified among the five ESBL-positive isolates, and they were ascribed to phylogroups A and B1. The intestinal tract of S. aurata might constitute a reservoir of ESBL-producing E. coli isolates.