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Broad-spectrum cephalosporin resistance is rapidly increasing in Escherichia coli, representing a food safety problem. The purpose of this paper is to characterize eight extended-spectrum-ß-lactamase (ESBL) and acquired AmpC ß-lactamase-producing E. coli isolates and virotypes associated, obtained from chicken and pork food samples in Puebla, Mexico.

Samples (36 from chicken and 10 from pork) were cultured on Levine agar plates supplemented with cefotaxime (2 mg/L) for isolation of cefotaxime-resistant (CTXR) E. coli. CTXR-E. coli isolates were detected in 33 of 46 samples (72 percent), and one isolate/sample was characterized (28 from chicken and 5 from pork), for ESBL production, phylogenetic group, sequence typing, resistance and virulence genes by PCR and sequencing.

Results showed 16 ESBL-E. coli (35 percent) (12/16 belonging to phylogroup B1) and 8 CMY-2-E. coli (17 percent). ESBL detected were as follows (number of isolates): CTX-M-2 (8); CTX-M-1 (2); CTX-M-15 (1); SHV-2a (4) and TEM-52c (1). In total, 20 different sequence types (STs) were identified among the ESBL- or CMY-2-producing E. coli strains, which included four new ones. The CTX-M-15 β-lactamase was detected in one E. coli ST617-ST10 Cplx-B1 strain that also carried ibeA gene. One CMY-2-positive strain of lineage ST224-B2 was detected and it carried the qnrA1 gene.

In this study, a ST131-based virotyping scheme for strains from food of animal origin was established since this kind of strains constitutes an important vehicle of virulent ESBL- and CMY-2-producing E. coli isolates, which could be transmitted to humans by direct contact or through the food chain.