title: Prevalence of beta-lactamases among ampicillin-resistant Escherichia coli and Salmonella isolated from food animals in Denmark.
abstract: The genetic background for beta-lactamase-mediated resistance to beta-lactam antibiotics was examined by PCR and sequencing in 160 ampicillin-resistant isolates (109 Escherichia coli and 51 Salmonella) obtained from healthy and diseased food animals in Denmark. Sequencing revealed three different variants of bla (TEM-1), of which bla (TEM-1b) was the most frequently detected (80 E. coli and 47 Salmonella), followed by bla (TEM-1a) (eight E. coli, one Salmonella) and bla (TEM-1c) (seven E. coli). A few isolates were found to express OXA, TEM-30, or PSE beta-lactamases. Mutations in the ampC promoter leading to increased production of the AmpC beta-lactamase were demonstrated in 11 cefoxitin-resistant or intermediate E. coli isolates. Nine of these isolates did not contain any bla (TEM) genes, whereas the remaining two did. No genes encoding SHV or extended-spectrum beta-lactamases were detected. Two new variants of bla (TEM) were detected, which have been designated bla (TEM-127) and bla (TEM-128). In TEM-127, amino acid 158 is substituted from His to Asn, whereas a substitution from Asp to Glu is seen at amino acid 157 in TEM-128. According to MIC determinations, these novel enzymes do not possess activity against extended-spectrum beta-lactams.
authors.affiliation: Danish Institute for Food and Veterinary Research, DK-1790 Copenhagen V, Denmark.
authors.forename: Inger
authors.initials: I
authors.lastname: Olesen
authors.forename: Henrik
authors.initials: H
authors.lastname: Hasman
authors.forename: Frank Møller
authors.initials: FM
authors.lastname: Aarestrup
mesh_terms: D000667:Ampicillin / Q000494:pharmacology; D000818:Animals; D000829:Animals, Domestic; D002417:Cattle; D002645:Chickens; D004926:Escherichia coli / Q000187:drug effects / Q000201:enzymology* / Q000235:genetics; D004927:Escherichia coli Infections / Q000382:microbiology; D008461:Meat Products / Q000382:microbiology*; D008826:Microbial Sensitivity Tests; D015995:Prevalence; D012475:Salmonella / Q000187:drug effects / Q000201:enzymology* / Q000235:genetics; D012480:Salmonella Infections / Q000382:microbiology; 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