Detection of Escherichia coli serogroups O26 and O113 by PCR amplification of the wzx and wzy genes

Abstract

PCR-based assays for detecting enterohemorrhagic Escherichia coli serogroups O26 and O113 were developed by targeting the wzx (O-antigen flippase) and the wzy (O-antigen polymerase) genes found in the O-antigen gene cluster of each organism. The PCR assays were specific for the respective serogroups, as there was no amplification of DNA from non-O26 and non-O113 E. coli serogroups or from other bacterial genera tested. Using the PCR assays, we were able to detect the organisms in seeded apple juice inoculated at concentration levels as low as < or =10 CFU/ml. The O26- and O113-specific PCR assays can potentially be used for typing E. coli O26 and O113 serogroups; these assays will offer an advantage to food and environmental microbiology laboratories in terms of identifying these non-O157 serogroups by replacing antigen-based serotyping.

FIG. 1.

PCR products in agarose gel showing the presence of E. coli O26 (panels A and B) and O113 (panels C and D) DNA in apple juice. The procedure was performed by using O26 wzx primers, fragment size 152 bp (A), using O26 wzy primers, fragment size 276 bp (B), using O113 wzx primers, fragment size 771 bp (C), using O113 wzy primers, fragment size 419 bp (D). Lane M, standard molecular weight size markers; lane 1, positive control; lane 2, negative control; lane 3, 10 CFU/ml concentration; lane 4, 10² CFU/ml concentration; lane 5, 10³ CFU/ml concentration; lane 6, 10⁴ CFU/ml concentration.