Molecular epidemiology of Streptococcus equi subsp. Zooepidemicus isolated from thoroughbred horses using multi locus sequence typing (MLST) in Korea

Background: Multi Locus Sequence Typing (MLST) is a new global molecular typing method used for analyzing the DNA polymorphisms in bacteria. In this study, using MLST, we analyzed the sequence profiles of Streptococcus (S.) zooepidemicus isolates from the Jeju and Jangsu provinces in South Korea. Objective: This study characterized the molecular epidemiology of S. zooepidemicus infection in Thoroughbred horses using MLST with an aim to control and prevent bacterial endometritis in mares. Methods: A total of 79 S. zooepidemicus isolates were included in this study. Sequencing of the 7 loci for the MLST analysis was performed as described in the MLST website manual (http:// pubmlst.org/szooepidemicus/) with some modifications. For each locus, every unique sequence was assigned a distinct allele number, and each Sequence Type (ST) was defined by a series of 7 integers (the allelic profile) corresponding to the alleles at the 7 loci (arcC, nrdE, proS, spi, tdk, tpi, and yqiL) using the MLST module in the Main Workbench. Results: Among the 79 isolates, 73 different MLST patterns were identified, each corresponding to 1-3 strains. The genetic relationships between the 79 isolates are presented in a dendrogram, and they diverged by up to 11% homology. At 11% homology, three MLST groups, M1, M2, and M3, were identified, and at 26% homology, five subgroups, L1-L5, were observed. We observed various MLST patterns in the strains isolated from Jeju and Jangsu. In addition, by estimating the epidemiological relationships among the strains isolated from Jangsu in 2007 and Jeju in 2009, which had similar MLST patterns, we determined that some strains from Jangsu may have been transported to Jeju. Conclusion: MLST can be used as a framework for determining the epidemiological relationships that form the genetic basis of host and infection site selection.