β-lactamases in ampicillin-resistant Escherichia coli isolates from foods, humans, and healthy animals

TEM-, SHV-, and OXA-type beta-lactamases were studied by PCR with 124 ampicillin-resistant (AMP(r)) Escherichia coli isolates recovered from foods of animal origin (n = 20) and feces of humans (n = 49) and healthy animals (n = 55). PCR showed that 103 isolates were positive for TEM and negative for SHV and OXA. Three E. coli isolates showed a positive reaction for OXA, and one showed a positive reaction for SHV. The remaining 17 E. coli isolates were negative for the three enzymes by PCR. Fifty-seven of the 103 bla(TEM) amplicons were sequenced. Different molecular variants of bla(TEM-1), were found in 52 isolates: bla(TEM-1a) (n = 9), bla(TEM-1b), (n = 36), bla(TEM-1c), (n = 6), and bla(TEM-1f) (n = 1). Four inhibitor-resistant TEM (IRT) beta-lactamase-encoding genes were also detected: bla(TEM-30c), (IRT-2), bla(TEM-34b) (IRT-6), bla(TEM-40b) (IRT-11), and bla(TEM-51a) (IRT-15). A new bla(TEM) genes named bla(TEM-95b), which showed a mutation in amino acid 145 (P-A) was detected. It was found in a food isolate of chicken origin (AMP(r), amoxicillin-clavulanic acid susceptible). The promoter region in 24 blaTEM amplicons was analyzed, and the weak P3 promoter was found in 23 of them (bla(TEM-1) in 20 amplicons and bla(TEM-51a), bla(TEM-30c), and bla(TEM-95b) in 1 amplicon each). The strong Pa/Pb promoter was found only in the bla(TEM-34b) gene. No extended-spectrum beta-lactamases were detected. Mutations at position -42 or -32 in the ampC gene promoter were demonstrated in 4 of 10 E. coli isolates for which the cefoxitin MIC was 16 mug/ml. Different variants of bla(TEM-1) and IRT blaTEM genes were found among the AMP(r) E. coli isolates from foods and the feces of humans and healthy animals, and a new gene, bla(TEM-95b) (P3), was detected.