High concentration of Shiga toxin 1-producing Escherichia coli isolated from Southern Thailand

Shiga toxin positive (stx^+) Escherichia coli were isolated from beef marketed in southern Thailand using an immunomagnetic separation (IMS) technique and detection on CHROMagar. A total of 6 stx^+ E. coli isolates were obtained from 10 beef samples. Four strains were serotype O157 and possessed the stx2 ^+ gene. The other two strains were non-O157 serotypes. Using the PCR technique, we demonstrated one strain possessed stx1 whereas the other contained stx2. Reverse passive latex agglutination was performed to investigate Stx production, it was found that stx1 ^+ E. coli (designated as PSU 5023), produced high levels of Stx1 (titre = 1: 2,048), but the other five stx2 ^+ strains were unable to produce Stx2 or produced it in too low amounts to detect (titre 2). Investigation of the Q gene using primers specific to the Q gene region of bacteriophage 933W revealed that only stx1 ^+ E. coli PSU 5023 possessed this gene. We suggest that this Q gene might promote high level production of Stx1. This is the first report of a high concentration of toxin from a Stx1-producing non- O157 strain of E. coli in Thailand and it is important for a public health warning.