Genetic characteristics of CTX-M-type extended-spectrum-β-lactamase (ESBL)-producing enterobacteriaceae involved in mastitis cases on Japanese dairy farms, 2007 to 2011

Abstract

Sixty-five CTX-M-2/15/14 extended-spectrum-β-lactamase-producing Enterobacteriaceae were isolated from 258,888 mastitic milk samples from Japanese dairy farms between 2007 and 2011. CTX-M-2-producing Klebsiella pneumoniae and CTX-M-15-producing Escherichia coli were the predominant strains isolated. There was no predominant clonal type, and clonal diversity was found even in strains isolated from a single farm.

Fig 1

RAPD-PCR of 41 K. pneumoniae isolates producing CTX-M-2. Cluster analysis was performed by the unweighted pair group method using arithmetic averages with a 1.0% band position tolerance window and 1.0% optimization. DNA relatedness was calculated based on the Dice coefficient. Thirty-two band patterns were typed using similarity cutoff values of approximately ≥85%.

Fig 2

PFGE patterns and cluster analysis of 13 CTX-M-producing E. coli isolates (MCE1 to 13) from mastitis cases, obtained using XbaI. Cluster analysis was performed by the unweighted pair group method using arithmetic averages with a 1.0% band position tolerance window and 1.0% optimization. DNA relatedness was calculated based on the Dice coefficient. Twelve band patterns were typed using similarity cutoff values of ≥90%. The Salmonella strain Braenderup CCUG50923 was used as a marker for assessing PFGE banding patterns. FCE3, -4, -5, and -16 were isolated from feces from cattle on farm M in our previous study (7).