Detection and Molecular Characterization of Escherichia coli CTX-M-15 and Klebsiella pneumoniae SHV-12 β-Lactamases from Bovine Mastitis Isolates in the United Kingdom

Abstract

ABSTRACTRecent reports raised concerns about the role that farm stock may play in the dissemination of extended-spectrum β-lactamase (ESBL)-producing bacteria. This study characterized the ESBLs in twoEscherichia coliand threeKlebsiella pneumoniaesubsp.pneumoniaeisolates from cases of clinical bovine mastitis in the United Kingdom. Bacterial culture and sensitivity testing of bovine mastitic milk samples identified Gram-negative cefpodoxime-resistant isolates, which were assessed for their ESBL phenotypes. Conjugation experiments and PCR-based replicon typing (PBRT) were used for characterization of transferable plasmids.E. coliisolates belonged to sequence type 88 (ST88; determined by multilocus sequence typing) and carriedblaCTX-M-15andblaTEM-1, whileK. pneumoniaesubsp.pneumoniaeisolates carriedblaSHV-12andblaTEM-1. Conjugation experiments demonstrated thatblaCTX-M-15andblaTEM-1were carried on a conjugative plasmid inE. coli, and PBRT identified this to be an IncI1 plasmid. The resistance genes were nontransferable inK. pneumoniaesubsp.pneumoniaeisolates. Moreover, in theE. coliisolates, an association of ISEcp1 and IS26withblaCTX-M-15was found where the IS26element was inserted upstream of both ISEcp1and theblaCTX-Mpromoter, a genetic arrangement highly similar to that described in some United Kingdom human isolates. We report the first cases in Europe of bovine mastitis due toE. coliCTX-M-15 and also of bovine mastitis due toK. pneumoniaesubsp.pneumoniaeSHV-12 β-lactamases in the United Kingdom. We also describe the genetic environment ofblaCTX-M-15and highlight the role that IncI1 plasmids may play in the spread and dissemination of ESBL genes, which have been described in both human and cattle isolates.