β-Lactamases in Ampicillin-Resistant Escherichia coli Isolates from Foods, Humans, and Healthy Animals

Abstract

ABSTRACT TEM-, SHV-, and OXA-type β-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) β-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 gene, 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 bla TEM 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 β-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 μg/ml. Different variants of bla TEM-1 and IRT bla TEM 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.