Modification of a multiple-locus variable number tandem repeat analysis (MLVA) for typing isolates of Erwinia amylovora

Erwinia amylovora, the causal agent of fire blight that affects economically important rosaceous plants, is reported among the most important plant pathogenic bacteria. The low genetic diversity within E. amylovora and the lack of simple and high-resolution genotyping techniques make epidemiology and evolutionary studies challenging for this pathogen. A multiple-locus variable number tandem repeat analysis (MLVA) based on a set of nine variable number tandem repeat loci was successfully used to type 46 E. amylovora isolates collected from different host plants in 16 countries, mainly Mediterranean. The nine polymorphic loci proved to have high discriminatory power and to increase the resolution of the MLVA. Thirty-eight haplotypes clustered in seven clonal complexes. The results identified potentially useful genetic markers among the Mediterranean strains, particularly from the Balkan Peninsula and the Eastern Mediterranean countries. Different MLVA types were observed amongst Italian strains only, indicating the possibility of multiple introductions of the disease. MLVA can be used effectively as a fast, cheap, and simple tool to track E. amylovora infection sources, to gain insight into geographic diversity, and to understand the dynamic evolution of the pathogen.