Abstract
The prevalence of pathogenic multi-drug resistant (MDR) extended-spectrum β-lactamase (ESBL)-producing Escherichia coli is rapidly increasing, becoming a global concern. In a veterinary context, ESBL-producing E. coli are mostly reported in poultry and pigs. Here, we report on the prevalence and characterize ESBL-producing E. coli isolated from diverse dairy farms in China. Overall, 36 (23.53%) out of 153 E. coli isolates from mastitic milk samples (n = 1252) were confirmed as ESBL-producers by double-disc synergy testing and PCR. Nucleotide analysis of PCR amplicons revealed that blaCTX-M was the predominant ESBL gene detected in 28 (77.78%) isolates, with blaCTX-M-15 being the major (78.57%) allele encoding for ESBLs. Also, 20 (55.56%) and 6 (16.67%) of the ESBL isolates were carrying blaTEM and blaSHV 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 (intI1) 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 dfrA17-aadA5 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 (ISCR1) 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 E. coli, particularly CTX-M-15, carrying clinical class 1 integrons and ISCR1 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 E. coli from mastitic cows in China.
Highlights
Bovine mastitis, inflammation of the mammary gland, is the most prevalent and economically important disease of dairy animals (Halasa et al, 2007)
Thirty six (23.53%) isolates were detected as ESBLproducing E. coli by phenotypic confirmatory tests and this was verified by ESBL genotype specific PCR assay
A national resistance surveillance study in China reported that the prevalence of ESBL-producing E. coli in humans has persisted above 50% since 2000 (Xiao et al, 2011), and recently Liu et al reported even higher prevalence (68.2%) of ESBLs in clinical E. coli isolates, mainly the blaCTX-M-15 (Liu et al, 2015)
Summary
Inflammation of the mammary gland, is the most prevalent and economically important disease of dairy animals (Halasa et al, 2007). Antimicrobial agents are used for therapeutic as well as preventive measures against bacterial infections including bovine mastitis in farm animals. Beta-lactams, such as ampicillin and amoxicillin, remain the first-line treatment in veterinary medicine but an increase in drug-resistance to these antibiotics has been observed. Extended-spectrum cephalosporins (ESC) such as ceftiofur have been approved in China for the treatment of animal diseases (MAO, 2010). Several recent studies have reported the increasing occurrence of highly resistant extendedspectrum β-lactamase (ESBL)-producing Enterobacteriaceae, mainly E. coli, isolated from food-producing animals from various countries including China (Rao et al, 2014; Xu et al, 2015; Seni et al, 2016)
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