Molecular and serological methods used by expert laboratories performing X. fastidiosa diagnosis meet high standards of efficiency and accurateness. These are the results of a first international quality assessment study carried out within a Euphresco initiative, in cooperation with POnTE and XF-ACTORS projects.
A Proficiency Testing recently concluded has gathered relevant information on the performance of 35 different laboratories involved in the detection of Xylella fastidiosa in plant samples, by using serological (ELISA – enzyme-linked immunosorbent assay) and molecular tests (PCR, qPCR). The laboratories are located in 18 different EPPO Countries in Europe and the Mediterranean Area. This is the first international external quality assessment study for laboratory performance of molecular and serological diagnosis of Xylella fastidiosa.
All the detailed information on the proficiency testing final report and results are available at this link.
The analysis of the result datasets showed that the performance of the majority of the laboratories was very satisfactory, with an accuracy rate higher than 90%, by using the currently available diagnostic protocols, i.e. recommended in the EPPO diagnostic protocol 7/24 (2). The highest accuracy values – trueness and precision of the results – were obtained for the molecular protocol based on real time PCR (qPCR), with 100% of accuracy reached in all participating laboratories that purified the DNA from the plant sap, using two of the protocols tested.
A lower number of proficient laboratories were recovered for conventional PCR and ELISA. In both cases the non-conform results were encountered with the samples containing the lowest bacterial concentration. Thus, while all laboratories performed proficiently with the most sensitive protocol (qPCR), the performance of some laboratories decreased using conventional PCR and ELISA, due to lack of detection in some contaminated samples (false negative).
The results recorded in the proficient laboratories were also analyzed in a test performance study (TPS) for the molecular tests. Likewise, the TPS results showed high reproducibility and accuracy values, underlining that, despite the tests were performed under different amplification conditions (i.e. each laboratory used its own instrument, reagents, etc.), they proved to be robust and highly reproducible. In conclusion, the most common and currently used detection protocols proved to be suitable for the accurate diagnosis of X. fastidiosa in plant materials.
The tests have been carried out within the framework of the EUPHRESCO initiative “Harmonized protocol for monitoring and detection of Xylella fastidiosa in host plants and vectors”, and in collaboration with the H2020 research projects POnTE and XF-ACTORS.