Molecular typing of Irish Streptococcus equi ssp equi strains

Streptococcus equi subsp. equi is the causative agent of strangles, a highly contagious upper respiratory infection of horses. A molecular typing scheme and database based on the variability of the S. equi SeM protein has been developed for use as an epidemiological tool to discriminate between S. equi strains. The majority of SeM alleles in the database are of UK origin. To date, there has been very little published material detailing the molecular epidemiology of S. equi isolates in any country other than the UK. The population of S. equi strains in Ireland had not been studied. This project was undertaken to identify and classify Irish strains of Streptococcus equi ssp equi within the Irish Horse Industry throughout Ireland. Using SLST (single locus sequence typing) based on the seM gene of Streptococcus equi ssp equi, 230 strains were analysed. Of these isolates 171 samples gave an amplicon. These amplicons were sequenced and the sequences analysed for similarities. A total of 163 samples gave robust sequence information. This analysis allowed division of the isolates into 20 groups, 12 of which contain at least 2 isolates and 8 groups containing single isolates. The sequences were compared to the Streptococcus equi seM database in the UK. The findings show that at least one of the groups is unique to Ireland, and some are most likely of UK origin, but many more are probably passed back and forth between the two countries. Analysis of the encoded protein sequences indicated that there were 17 positions where there were amino acid changes between different groups. However, it is unlikely that these changes alter the fibrinogen binding properties of the SeM protein