ESBL-Producing from Cows Suffering Mastitis in China Contain Clinical Class 1 Integrons with CTX-M Linked to IS.

The prevalence of pathogenic multi-drug resistant (MDR) extended-spectrum β-lactamase (ESBL)-producing is rapidly increasing, becoming a global concern. In a veterinary context, ESBL-producing are mostly reported in poultry and pigs. Here, we report on the prevalence and characterize ESBL-producing isolated from diverse dairy farms in China. Overall, 36 (23.53%) out of 153 isolates from mastitic milk samples ( = 1252) were confirmed as ESBL-producers by double-disc synergy testing and PCR. Nucleotide analysis of PCR amplicons revealed that was the predominant ESBL gene detected in 28 (77.78%) isolates, with being the major (78.57%) allele encoding for ESBLs. Also, 20 (55.56%) and 6 (16.67%) of the ESBL isolates were carrying and genes, respectively, in singlet or in combination. The majority of these isolates belonged to phylo-group A (69.44%) and D (16.67%). Strikingly, all these isolates were found to be MDR showing high resistance to cephalosporins including the fourth generation cefepime and common non β-lactams. Additionally, class 1 integrons () were found in 30 (83.33%) isolates. Analysis of the class 1 integrons variable regions indicated that they were carrying up to five different gene cassettes conferring resistance to various drugs with a predominant combination of genes in tandem, conferring resistance to aminoglycosides and trimethoprim. However, no ESBL encoding genes were found in the cassettes. Interestingly, 22 (66.11%) of the ESBL isolates were also carrying insertion sequence common region 1 (IS) which was found to be associated with most of the CTX-M genes. Altogether, the current study reports on the high prevalence of ESBL-positive , particularly CTX-M-15, carrying clinical class 1 integrons and IS elements are likely indicative of their rapid and wider dissemination, posing threats to veterinary and public health. To the best of our knowledge, this is the first comprehensive study to report on the alarming high occurrence of ESBL-producing from mastitic cows in China.