Occurrence of Bovine Mastitis Caused by CTX-M-2 ^|^beta;-Lactamase Producing Klebsiella pneumoniae

Abstract

The aims of this study were to determine the presence of Enterobacteriaceae strains producing CTX-M-type extended-spectrum beta -lactamases (ESBLs) (CTX-M) involved in bovine mastitis among Japanese dairy cattle and clinical courses of cows affected by the mastitis. Between August 2006 and January 2007 we chose 51 cefazolin-resistant isolates from oxidase-negative, Gram-negative bacilli isolates obtained from 30,237 quarter milk samples from 20,194 cows with mastitis in 1,000 dairy farms in Nemuro Subprefecture of Hokkaido Prefecture, Japan. They were screened for ESBLs using the standard Clinical and Laboratory Standards Institute (CLSI) ESBLs confirmatory combination disc tests. We performed genotyping of CTX-M-, TEM-, and SHV-type beta -lactamases by PCR analysis and nucleotide sequencing, and determined the minimum inhibitory concentrations (MICs) of 21 antimicrobials. We identified three Klebsiella pneumoniae isolates producing CTX-M-2 from three quarters of two cows with mastitis in two dairy farms. One cow had mild acute clinical mastitis (slight swelling, warmth and hardness of the udder, slightly watery foremilk with flakes) without systemic symptoms and resolved within 4 weeks of diagnosis. Another cow had severe acute clinical mastitis with systemic symptoms and resolved within 10 weeks of diagnosis. The three isolates exhibited resistance to ampicillin, cefazolin, cefuroxime, cefotaxime, ceftriaxone, cefpodioxime, ceftiofur, cefquinome, kanamycin, and oxytetracycline. Conversely, they were susceptible to ceftazidime, cefmetazole, moxalactam, imipenem, aztreonam, gentamicin, trimethoprim-sulfamethoxazole, and enrofloxacin. This is the first report on CTX-M-producing K. pneumoniae involved in bovine mastitis in Japan.