Multilocus variable number tandem repeat analysis of E dwardsiella piscicida isolates pathogenic to fish

This study describes a novel multilocus variable number tandem repeat analysis ( MLVA ) based on six variable number of tandem repeat ( VNTR ) loci for genotyping of 37 E dwardsiella piscicida (previously E dwardsiella tarda ) isolates from multiple sources. The number of alleles identified for each of the six VNTR loci ranged from 3 to 5 with VNTR loci 1 ( DI  = 0.632) and 3 ( DI  = 0.644), displaying the highest degrees of polymorphism. MLVA typing of the 37 E . piscicida isolates resulted in the identification of five major clusters consistent with their geographical origins, and were designated as MLVA types I , II , III , IV and V . Types III and V were resolved further into subtypes largely consistent with outbreak source. An MLVA profile comprising a string of integers representing the number of tandem repeats for each allele provided a unique identification for each MLVA type and/or strain. The MLVA protocol described in the current study is robust, relatively simple, has a higher power of resolution than multilocus sequence analysis ( MLSA ) and is capable of discriminating closely related isolates.