Molecular epidemiological study on emerging enteric infections in Asia

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We studied the DNA fingerprints of new pandemic strains of Vibrio parahaemolyticus isolated in Thailand and Vietnam by using the pulsed field gel electrophoresis(PFGE) method. The results indicated that strains harbored in molluscan bivalves are responsible for infection in Thailand and that clear transition of O3:K6 serotype to O1:K25,etc. occurred in Vietnam. The nucleotide sequences of 11 genes in 60 pandemic strains representing the isolates in various Asian countries were combined and analyzed. The result indicated that O3:K6,O4:K68, and O1:KUT strains are phylogenetically related and possible ancestral strains of the pandemic strains were found.Of the 20 ctx^+ Vibrio cholerae strains isolated from the seafoods in Malaysia 15 strains belonged to the new serotype (O139). These strains and ctx^+ V.cholerae strains isolated in India and Bangladesh and from international travelers were subjected to the PFGE-dendrogram analysis. The phylogenetic relationship among these strains suggested that Malaysian O139 strains were introduced from the Bengal area in two separate occasions. The nucleotide sequences of five genes of 79 strains of V.cholerae including the above strains were determined and analyzed by a multilocus sequence typing approach. The result supported the phylogenetic relationship of the strains obtained by the PFGE method.Our study on Escherichia coli O157 suggested this organism is widely distributed in Asian environment. However, considerable number of the environmental strains produced very little amount of Stx2. This was due at least in part to the change in the DNA sequence around the Q gene. This genetic change and the fact that very few patients infected by E.coli O157 are reported in Asian countries appear to be related.