Virulence determinants and antimicrobial resistance of E. coli isolated from bovine clinical mastitis in some selected dairy farms of Bangladesh

Abstract

<i>E. coli</i> is one of the major significant pathogens causing mastitis, the most complex and costly diseases in the dairy industry worldwide. Present study was undertaken to isolate, detect the virulence factors, phylogroup, antimicrobial susceptibility and antimicrobial resistance genes in <i>E. coli</i> from cows with clinical mastitis. A total of 68 milk samples comprising 53 from clinical mastitis and 15 from apparently healthy cattle were collected from four different established dairy farms in Bangladesh. <i>E. coli</i> was isolated from the milk samples and identified by PCR targeting <i>malB</i> gene and sequencing of 16S rRNA gene. <i>E. coli</i> isolates were screened by PCR for the detection of major virulence genes (<i>stx</i>, <i>eae</i> and <i>cdt</i>) of diarrheagenic <i>E. coli</i> followed by phylogenetic grouping. Antimicrobial susceptibility of the <i>E. coli</i> isolates was determined by disk diffusion test and <i>E. coli</i> showing resistance was further screened for the presence of antimicrobial resistance genes. <i>E. coli</i> was isolated from 35.8% of the mastitis milk samples but none from the apparently healthy cattle milk. All the <i>E. coli</i> isolates were negative for <i>stx</i>, <i>eae</i> and <i>cdt</i> genes and belonged to the phylogenetic groups A and B1 which comprising of commensal <i>E. coli</i>. Antibiotic sensitivity testing revealed 84.2% (16/19) of the isolates as multidrug resistant. Highest resistance was observed against amoxicillin (94.5%) followed by ampicillin (89.5%) and tetracycline (89.5%). <i>E. coli</i> were found resistant against all the classes of antimicrobials used at the farm level. Tetracycline resistance gene (<i>tetA</i>) was detected in 100% of the tetracycline resistant <i>E. coli</i> and <i>bla</i>TEM-1 was present in 38.9% of the <i>E. coli</i> isolates. Findings of this study indicate a potential threat of developing antimicrobial resistance in commensal <i>E. coli</i> and their association with clinical mastitis. Occurrence of multidrug resistant <i>E. coli</i> might be responsible for the failure of antibiotic therapies in clinical mastitis as well as pose potential threat of transmitting and development of antibiotic resistance in human.