THE MOLECULAR DIFFERENTIATION OF RENIBACTERJUM SALMONINARUMISOLATES

Studies were undertaken to examine the extent of molecular variation among isolates of the fish pathogen Renibacterium sa/moninarum. As many isolates as possible were gathered from diagnostic laboratories within the UK, and checked for viability and contamination. The isolates were derived mainly from infected rainbow trout and Atlantic salmon that were farmed in England, Scotland and Wales, subject to the requirements of statutory legislation. Incomplete histories were available for the sources of the isolates, which spanned a time scale of 36 years, from 1962-1998. Molecular variation between the isolates was examined using two strategies. Firstly, defined regions of the genome were examined for polymorphisms. PCR analysis of previously characterised genes, msa, hly, and rsh, revealed no length polymorphisms among 43 UK isolates of R. salmoninarum. The 23S and SS rRNA genes were sequenced and sequence analysis of the 16S-23S (ITS I) and 23S-SS (ITS2) rRNA regions was performed. Sequence analysis confirmed the correct taxonomic placement of R. salmoninarum within the Micrococcus/Arthrobacter subdivision of the Actinomycetes. Some isolates possessed small sequence variations within ITS I that can provide an indication of their geographical origins. Sequence variation also exists in the ITS