Prevalence and virulence gene profiling of shigatoxigenic Escherichia coli 0157:H7 strains isolated from cattle

Abstract

Escherichia coli and isolates belonging to serotypes O157 are Gram negative, rod shaped bacteria that have received a lot of attention recently due to their potential to cause life threatening sporadic incidents and outbreaks of infections in humans worldwide. The aim of this study was to determine the prevalence and virulence of gene profiles of Shiga-toxigenic Escherichia coli O157:H7 strains isolated from cattle. A total of 500 faecal samples were collected from cattle in both communal and commercial farms in the North West province, South Africa. Isolation of E. coli was done by sub-culturing a loop full of the bacterial colony onto Sorbitol Mac-Conkey agar (Bio lab, South Africa) supplemented with cefixime and potassium tellurite (SMAC-CT). Identification of E. coli isolates were performed using preliminary (serological assay) and confirmatory (PCR assay) tests. Antibiotic susceptibility test was performed using the Kirby-Bauer disc diffusion method to determine the resistance profile of the isolates against a panel of seven different antimicrobial agents (Ciprofloxacin, Gemifloxacin, Levofloxacin, Moxifloxacin, Tetracycline, Penicillin and Norfloxacin). From 326 isolates, 119 were positive for serological assay and 62 isolates were found positive uidA gene fragment. Of those 62 isolates, 5 (83.3%) isolates were from Rooigront farm, 3 (37.5%) from Molelwane farm, 16 (80%) from Lokaleng farm, 16 (100%) from Rooigrond prison farm, 6 (66.6%) from Klippan, 15 (37.5%) from Ottosdal farm and 1 (5%) was from Zeerust. Fifty isolates were found positive for rfbO157 gene fragment. Of these 50 isolates, 3 (6%) isolates from farm, 3 (37.5%) from Molelwane farm, 16 (80%) from Lokaleng farm, 8 (50%) from Rooigrond prison farm, 5 (55.5%) from Klippan, 15 (37.5%) from Ottosdal farm and 0 (0%) from Zeerust. Fifty-five (55) of confirmed E. coli O157:H7 isolates were positive for shiga-toxins genes of which 30 (60%) isolates carried stx1 virulene gene while 25 (50%) carried stx2 gene. The persistence- of other virulence genes. Iha, toxB, katP, espP, tir and terD genes were confirmed in 7 (14%), 9 (18%), 5 (10%), 13 (26%), 11 (22%) and 50 (100%) isolates respectively. In the present study most of the isolates were found to be resistant to tested antimicrobial agents. Most isolates were resistant towards Ciprofloxacin (40%), Amplicillin (100%) and Moxifloxacin (28%), while all the isolates were found susceptible to Levofloxacin, Tetracycline, Gemifloxacin and Norfloxacin. Multiple antibiotic resistant (MAR) phenotypes AP-C-M were dominant in all the tested isolates. Therefore, hypothetically it can be concluded that the bacterial isolates did have the STECvirulence strains within their host which were then able to be expressed in the presences of antimicrobial agents especially those that are frequently utilized in veterinary and human medicine.