Analysis of environmental Escherichia coli isolates for virulence genes using the TaqMan PCR system

Abstract

Aims: To assess the presence of virulence genes in environmental and foodborne Escherichia coli isolates using the TaqMan PCR system.

Methods and results: Three TaqMan pathogen detection kits called O157:H7, StxI and StxII were used to investigate the presence of virulence genes in Escherichia coli isolates. All 54 foodborne E. coli O157:H7 isolates showed expected results using these kits. Ninety (15%) of 604 environmental isolates gave positive amplification with an O157:H7-specific kit. TaqMan PCR amplification products from these 90 isolates were analysed by agarose gel electrophoresis, and 90% (81 of 90) of the environmental samples contained the expected PCR product. Sixty-six of these 90 were chosen for serotyping tests and only 35% (23 of 66) showed agglutination with both anti-O157 and anti-H7 antibodies. Further ribotyping of 16 sero-positive isolates in an automated Riboprinter did not identify these to be O157:H7. Multiplex PCR with primers for eaeA, stxI and stxII genes was used to confirm the TaqMan results in 10 selected environmental isolates.

Conclusions: All three TaqMan pathogen detection kits were useful for virulence gene analysis of prescreened foodborne O157:H7 isolates, while the O157:H7-specific kit may not be suitable for virulence gene analysis of environmental E. coli isolates, because of high false positive identification.

Significance and impact of the study: The ability to rapidly identify the presence of pathogenic E. coli in food or environmental samples is essential to avert outbreaks. These results are of importance to microbiologists seeking to use TaqMan PCR to rapidly identify pathogenic E. coli in environmental samples. Furthermore, serotyping may not be a reliable method for identification of O157:H7 strains.