European protocol for diagnosis of Erwinia amylovora

Abstract

The EU-funded project DIAGPRO has developed diagnostic protocols for 18 quarantine pests including Erwinia amylovora. The protocol for this organism includes a diagnosis scheme for detection of the bacterium in symptomatic and asymptomatic plants with details of the different techniques as isolation in three media, direct tissue print-ELISA, enrichment DASI-ELISA, immunofluorescence, conventional PCR and nested-PCR in a single closed tube (before and after enrichment of the samples in two liquid media). A ring test was conducted to evaluate and standardize some techniques and protocols. Testing was performed independently at 10 plant health laboratories analysing 15 samples (healthy, spiked or inoculated). The reliability of the diagnosis across all laboratories decreased with inoculum concentration. The accuracy of the different techniques, defined as (true positive diagnosis + true negatives)/total number of samples, was: 0.88, 0.92 and 0.92 respectively for isolation on King’s B, SNA and CCT media; 0.70, 0.72 and 0.66 for immunofluorescence performed with one monoclonal and two polyclonal antibodies commercially available; 0.79 and 0.83 for enrichment-ELISA with a commercial kit after enrichment in two media; 0.51 for conventional PCR and 0.69 for nested-PCR in a single tube, both techniques increasing their accuracy up to 0.78 and 0.86, respectively, after enrichment. The designed protocol is freely available at the web site: www.csl.gov.uk/science/organ/ph/diagpro.