title: Beta-lactamases in ampicillin-resistant Escherichia coli isolates from foods, humans, and healthy animals.
abstract: 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) 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 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 micro g/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.
authors.affiliation: Area de Bioquímica y Biología Molecular, Universidad de La Rioja, 26006 Logroño, Spain.
authors.forename: Laura
authors.initials: L
authors.lastname: Briñas
authors.forename: Myriam
authors.initials: M
authors.lastname: Zarazaga
authors.forename: Yolanda
authors.initials: Y
authors.lastname: Sáenz
authors.forename: Fernanda
authors.initials: F
authors.lastname: Ruiz-Larrea
authors.forename: Carmen
authors.initials: C
authors.lastname: Torres
mesh_terms: D000667:Ampicillin / Q000494:pharmacology; D000818:Animals; D000829:Animals, Domestic; D002417:Cattle; D002645:Chickens; D004285:Dogs; D004926:Escherichia coli / Q000187:drug effects* / Q000201:enzymology / Q000302:isolation & purification; D004927:Escherichia coli Infections / Q000382:microbiology*; D005243:Feces / Q000382:microbiology*; D006801:Humans; D008461:Meat Products / Q000382:microbiology*; D008826:Microbial Sensitivity Tests; D008969:Molecular Sequence Data; D016133:Polymerase Chain Reaction; D017422:Sequence Analysis, DNA; D013552:Swine; D018440:beta-Lactam Resistance; D001618:beta-Lactamases / Q000235:genetics* / Q000378:metabolism; D047090:beta-Lactams / Q000494:pharmacology
chemical_list: D047090:beta-Lactams; D000667:Ampicillin; D001618:beta-Lactamases