A comparison of alkaline phosphatase and radiolabelled gene probes with bioassays for enterotoxigenic Escherichia coli

Abstract

Alkaline phosphatase-conjugated oligonucleotide probes (APO), 32P-labelled oligonucleotide (RO) and cloned polynucleotide (RP) probes were evaluated for their ability to detect enterotoxigenic Escherichia coli (ETEC) as defined by bioassay. These three sets of probes were applied to 301 E. coli strains that had previously been defined by the Y1 adrenal cell assay for heat-labile enterotoxin (LT) and the infant mouse assay for heat-stable enterotoxin (ST). The correlation of the APO probe for LT with the bioassay was 98% with five discrepancies and a positive predictive value (PPV) of 100%. For the APO/ST probe the correlation with the bioassay was 98% with seven discrepancies and a PPV of 96%. The correlation of the RO probe for LT was 99% with four discrepancies and a PPV of 100%, while the overall correlation for the two RO/ST probes was 97% with eight discrepancies and a PPV of 97%. For the RP probes, the correlation for LT was 99% with four discrepancies and a PPV of 100% and for ST was 98% with seven discrepancies and a PPV of 98%. These findings suggest that the APO probes were as sensitive as the RO and RP probes in detecting ETEC by colony hybridization and could be a practical alternative to bioassays and radiolabelled probes for ETEC since they do not require expensive equipment or extensive technical training.