Chemiluminescent and colorimetric detection of Erwinia amylovora by immunoenzymatic determination of PCR amplicons from plasmid pEA29.
A molecular diagnostic technique (polymerase chain reaction enzyme-linked immunosorbent assay [PCR-ELISA]) for detection of Erwinia amylovora was developed. The protocol is based on the immunoenzymatic determination of PCR products. For in vitro amplification, previously published primers able to detect the cryptic plasmid pEA29, which is ubiquitous in E. amylovora, were used. Amplicons were labelled with 11-digoxigenin (DIG)-dUTP during the amplification reaction, captured by hybridization to a biotinylated oligonucleotide in streptavidin-coated ELISA microplates, and then detected with anti-DIG-Fab′-peroxidase conjugated antibodies. The specificity of the assay was verified using E. amylovora strains from different host plants (pear cultivars) and geographical origins in addition to other plant-associated bacteria (either phytopathogenic or saprophytic) belonging to the genera Erwinia, Pseudomonas, and Agrobacterium. In detection threshold experiments with pure cultures, as few as 30 and 3 CFU/reaction tube were detected when the ABTS (colorimetric) and ECL (chemiluminescent) detection assays, respectively, were used. PCR-ELISA coupled with chemiluminescent detection was able to detect as few as 4×102 CFU/g of artificially infested pear twigs. The assay was further shown to be suitable for detection of E. amylovora in naturally infected plant organs, and the results were compared to those obtained using standard PCR assays with electrophoretic separation of amplicons.