CTX-M-15-Type Extended-Spectrum Beta-Lactamase-Producing Escherichia coli as Causative Agent of Bovine Mastitis.

In the present study, 3 quarter milk samples from 3 cows showing clinical signs of mastitis were investigated. Three Escherichia coli were isolated and were found resistant to ceftiofur and cefquinome. The isolates were detected as extended-spectrum beta-lactamase (ESBL) producers by the Clinical and Laboratory Standards Institute (CLSI) ESBL screening test and combined disc method. CTX-M- and TEM-type beta-lactamase genes (blaCTX-M blaTEM) were detected by polymerase chain reaction in the isolates. Sequencing of blaCTX-M and blaTEM genes showed that the isolates were both TEM-1- and CTX-M-15-type beta-lactamase producers. The isolates were tested by agar disc diffusion test for susceptibility to various classes of antibiotics (aminoglycosides, quinolones, phenicols, folate pathway inhibitors, and tetracyclines), and they were determined as multidrug resistant. Therefore, this is the first report indicating the involvement of multidrug-resistant CTX-M-15-type ESBL-producing E. coli as a cause of bovine mastitis in Turkey.