Molecular characterization of antimicrobial resistance and virulence genes of isolates from bovine mastitis.

BACKGROUND AND AIM

Mastitis is a common and economically important disease in dairy cattle. It remains one of the most common reasons for the extensive use of antimicrobials in dairy farms leading to the emergence of antimicrobial-resistant pathogens. The aim of this study was to determine the patterns of antimicrobial resistance of isolates from bovine mastitis and to identify prominent antimicrobial resistance and virulence genes among isolated strains.

MATERIALS AND METHODS

Antimicrobial susceptibility testing against six antibiotic groups, including tetracyclines, aminoglycosides, beta-lactams, macrolides, sulfonamides, and fluoroquinolones was performed using the disk diffusion method. PCR was performed on resistant isolates to detect resistance and virulence genes using commercially available primers.

RESULTS

Out of 216 milk samples cultured, 14 samples yielded isolates. All isolates (100%) were resistant to ampicillin, amoxicillin, procaine penicillin, streptomycin, oxytetracycline, and sulfamethoxazole-trimethoprim. Only one isolate (7%) was sensitive to gentamicin, and all isolates (100%) were sensitive to enrofloxacin and ciprofloxacin. All isolates carried at least one resistance gene against one or more of the major antibiotic groups. All isolates carried the , and genes, followed by (93%), (86%), (86%), (78%), (71%), (57%), (57%), and (36%). The lowest percentage of isolates carried (17%) and bla2 (12%) genes, and none of the isolates carried the gene. Most of the isolates (93%) carried the Shiga toxin 1 virulence gene, followed by complement resistance protein (79%), intimin (64%), Shiga toxin 2 (36%), cytotoxic necrotizing factor (35%), aerotaxis receptor (21%), and type 1 fimbriae (15%).

CONCLUSION

Results of this study indicate that the high percentages of isolate from bovine mastitis are resistant to two or more of the major antibiotic groups, irrespective of the presence or absence of relevant resistance or virulence genes.