Shiga Toxin-ProducingEscherichia coliIsolated from Bovine Mastitic Milk: Serogroups, Virulence Factors, and Antibiotic Resistance Properties

Abstract

The aim of this study was to detect the virulence factors, serogroups, and antibiotic resistance properties of Shiga toxin-producingEscherichia coli, by using 268 bovine mastitic milk samples which were diagnosed using California Mastitis Test. AfterE. coliidentification, PCR assays were developed for detection of different virulence genes, serogroups, and antibiotic resistance genes ofEscherichia coli. The antibiotic resistance pattern was studied using disk diffusion method. Out of 268 samples, 73 (27.23%) were positive forEscherichia coli, and, out of 73 positive samples, 15 (20.54%) were O26 and 11 (15.06%) were O157 so they were the highest while O111 was not detected in any sample so it was the lowest serogroup. Out of 73 STEC strains, 11 (15.06%) and 36 (49.31%) were EHEC and AEEC, respectively. All of the EHEC strains hadstx1,eaeA, andehly, virulence genes, while in AEEC strainsstx1had the highest prevalence (77.77%), followed byeaeA(55.55%). Totally,aadA1(65.95%) had the highest whileblaSHV(6.38%) had the lowest prevalence of antibiotic resistance genes. The disk diffusion method showed that the STEC strains had the highest resistance to penicillin (100%), followed by tetracycline (57.44%), while resistance to cephalothin (6.38%) was the lowest.