Characterization of extended-spectrum beta-lactamase (ESBL)-carrying plasmids and clones of Enterobacteriaceae causing cattle mastitis in France

Extended-spectrum beta-lactamases (ESBLs) have become widespread enzymes in food-producing and companion animals worldwide. However, in cattle mastitis, a major cause of economic loss in the dairy industry, ESBL-producers were rarely described. In this study, from a collection of 1427 Escherichia coli and Klebsiella pneumoniae isolates causing clinical mastitis in France, we report 0.4% (6/1427) of the isolates carrying an ESBL gene. These six isolates were genetically unrelated and recovered over a 3-year period of time. The blaCTX-M-14 gene was found in 4/6 isolates, and was predominantly located on F2:A-:B- IncFII plasmids. The blaCTX-M-1 IncI1/ST3, which is widespread in various animal species in France, was found as well. Interestingly, among the five E. coli isolates, the ST23 and ST58 clones were found twice, together with the ST10 clone, all of which were previously found as ESBL-carriers in humans. Despite the very limited number of ESBL-producers recovered, this study shows a surprisingly low molecular diversity of the strains causing mastitis in France with respect to ESBL genes, plasmids and clones. Further work is needed to understand the major driving forces of the ESBL epidemiology in animals, including for different infections within the same animal species.