Prevalence of Shiga-toxigenic <em>Escherichia coli</em> in Mauritian dairy cattle

Abstract

Shiga-toxigenic Escherichia coli (STEC) are important human pathogens (1). They are characterized by their ability to pro­duce Shiga toxins (stx1 and stx2). Seven STEC have been shown to withstand food processing procedures that are expected to ensure food safety. Clinical symptoms associated with STEC infection can vary from abdominal cramps and acute bloody diarrhea to more severe aftereffects including hemorrhagic coli­tis, hemolytic uremic syndrome and thrombocytopenic purpura, which can lead to kidney failure and death.Dairy cattle, which excrete STEC in their feces, are a major source of STEC infection (2). Humans become infected with STEC through direct contact with infected animals or by inges­tion of contaminated water, raw and unpasteurized milk, meat products, and/or plant-derived products (4–6). The objectives of this study were to estimate both cow-level and farm-level point prevalence estimates of STEC fecal shedding in Mauritian dairy cattle and to characterize putative STEC isolates based on their virulence factors.A cross-sectional study was conducted to investigate the preva­lence of STEC in the dairy cattle population of Mauritius. Fecal samples were collected from 150 individual dairy cattle from 38 dairy farms located throughout the nine district regions of the island. Collected samples were enriched in modified Tryptic Soy broth followed by isolation on CHROMagarTM STEC (3). Suspected isolates were streaked onto EMB agar, further puri­fied on nutrient agar and subsequently cryopreserved in glyc­erol until further investigation. Putative isolates were charac­terized using molecular techniques (7, 8) for the presence of chromosomal sequences encoding Shiga toxin genes (stx1 and stx2), the intimin protein (eaeA) and the plasmid-encoded hemo­lysin (hlyA).Out of the 38 farm samples, 29 farms (76%) were found to be positive for presumptive STEC isolates. From the 150 fecal samples collected, 111 (74%) were found to harbor presump­tive STEC isolates (Table I). Polymerase-chain-reaction- (PCR-) based characterization has confirmed the presence of STEC in a number of fecal samples. Results obtained so far indicate that STEC are common members of the gut microbiome of dairy cattle in Mauritius.Presumptive STEC isolates are currently being screened with PCR targeting stx1, stx2, eaeA and hlyA genes. This epidemiological study on STEC is the first of its kind in Mauritius and in the Indian Ocean region. It aims at providing new information concerning the presence of STEC in Mauritian dairy cattle. It involves the use of the latest chromogenic agar (CHROMagarTM STEC) available on the market. This culture medium has been designed for the detection of a wide range of STEC from different sources. The study highlights the importance of implementing proper sanitary measures at the dairy farm level to prevent cross contamination of milk and the surrounding environment.