Prevalence of shiga toxin-producing Escherichia coli in feces and raw milk of domestic cattle and sheep

A total of 1060 samples of raw milk and fecal from cattle and sheep were collected from farms in the Taiwan area between September 1997 and June 1998. Shiga toxin-producing E. coli (STEC) strains were isolated based on the demonstration of Vitek automicrobic system and shiga toxin-PCR after enrichment and selective procedures. The results showed that 0.4% of 231 raw milk samples were contaminated with STEC. Among the 829 fecal samples of cattle and sheep, 9% tested positive for STEC. A total of 121 STEC strains were selected and further analyzed for biochemical tests, serotype and pathogenic genes of eaeA (attaching and effacing) as well as hlyA (enterohemolysis). Results revealed that only 3% of strains lacked β-D-glucuronidase activity and 4% of strains were unable to ferment sorbitol. Thirteen percent of strains were typed as O6, O8, O15, O78, O112ac, O128, O157 and O159 with 43 O-antisera. The remaining strains were non-typeable with O-antisera. Thirty one percent of strains were determined as H2, H7, H10, H16, H19, H21, H42, H45 and H51 with 22 H-antisera. Three types of shiga toxin genes were detected with different rates, namely slt1, 39%; slt2, 33% and slt1+slt2, 28%. Seventy percent of STEC strains harbored hlyA gene and 1.6% possessed hlyA and eaeA genes. In addition, one E. coli O157:H7 strain, isolated from feces of domestic sheep, carried slt2, hlyA and eaeA genes. This study indicates that the feces of cattle and sheep were most likely the source of STEC in the Taiwan area.