Erwinia amylovora, the bacterium that causes fire blight, occurs throughout North America, from where it probably originated, and in 34 countries worldwide. Little is known about the phenotypic and genetic relatedness of the bacterium on various hosts and in different geographic locales. Our laboratory is currently involved in a phenotypic, biochemical, and genetic characterization of a worldwide collection of fire blight isolates collected from 21 countries on 13 host genera. Gross phenotypic and genetic analysis has been conducted on the collection including: Gram status, colony description on Crosse-Goodman (C-G) diagnostic medium, and PCR analysis of the Pea29 plasmid. Results from Gram tests have revealed a number of isolates which may not belong to the E. amylovora species, while platings on C-G medium and PCR-based Pea29 screenings suggest the presence of typical and some atypical isolates which differ by colony surface characteristics and by formation of plasmid based PCR products. Preliminary metabolic fingerprinting studies have also revealed at least 2 phylogenetic clusters based on differences in nutrient utilization patterns. Research is currently underway to investigate the genetic relatedness of these isolates based on DNA sequence analysis of hypervariable regions on the bacterial chromosome. The results of these studies should facilitate a better understanding of the geographic and phylogenetic relatedness of E. amylovora occurring around the world as well as aid in the identification of spurious isolates, which may not be true members of the E. amylovora group.
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