Co-Occurrence of Plasmid-Mediated Colistin Resistance () and Extended-Spectrum -Lactamase Encoding Genes in from Bovine Mastitic Milk in China.

Both phosphoethanolamine transferase enzymes and extended-spectrum -lactamases (ESBLs) are the main plasmid-mediated mechanisms of resistance to colistin and third-generation cephalosporins, respectively, and currently considered a major concern to humans and food animals. Prevalence of gene in from dairy cattle has rarely been reported. Our objective was to determine prevalence and characteristics of carrying isolated from clinical mastitis cases in large dairy farms (>500 cows) in 16 provinces of China. A total of 249 was isolated from 2,038 mastitic milk samples. Among these isolates, 2.0% ( = 5) and 19.7% ( = 49) were colistin resistant -positive and ESBL-producing isolates, respectively. All -positive isolates that produced ESBLs also carried the gene and belonged to phylogroup-A. Most and genes were located on conjugative plasmids (IncP and IncF, respectively) that were successfully transferred to transconjugants in conjugation experiments. All -positive isolates were multidrug resistant, exhibiting resistance to common antimicrobials. Multilocus sequence typing of these carrying isolates revealed four sequence types, reflecting substantial diversity. Multilocus sequence analysis detected evolutionary connection of 1 carrying isolates with our recently reported ESBL-producing isolates, raising concerns regarding fast dissemination between bacteria. To our knowledge, this was the first nation-wide report describing isolates of from mastitic milk samples collected on large dairy farms in China, carrying and genes on conjugative plasmids. We concluded that dairy cattle are a potential source of -carrying and ESBL-producing .