JCM Accepts, published online ahead of print on 17 June 2009

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J. Clin. Microbiol. doi:10.1128/JCM.00223-09
Copyright (c) 2009, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

Multiple locus variable number of tandem repeat analysis of Salmonella enterica serovar Typhi

Sophie Octavia and Ruiting Lan^*

School of Biotechnology and Biomolecular Sciences, University of New South Wales, Sydney, NSW 2052, Australia

^* To whom correspondence should be addressed. Email: r.lan{at}unsw.edu.au.

Multilocus variable number of tandem repeats (VNTRs) analysis (MLVA) is widely used as molecular markers to differentiate isolates of homogenous pathogenic clones. We explored the genomes of Salmonella enterica serovar Typhi strains CT18 and Ty2 for potential VNTRs. Among the forty-three identified, two were found to be polymorphic. Together with seven polymorphic VNTRs from previous studies, they were used to type 73 global Typhi isolates. A total of 70 MLVA profiles were found, distinguishing all except three pairs of isolates into individual profiles. The discriminatory power was 0.999. Phylogenetic analysis showed that the MLVA profiles can be divided into seven clusters. However, except for the closely related isolates the relationships derived were in conflict with that inferred from Single Nucleotide Polymorphism (SNP) typing using 38 SNPs done previously. We concluded that MLVA can only resolve the relationships among closely related isolates. A combination of SNP typing and MLVA typing offers the best approach for local and global epidemiology and the evolutionary analysis of Typhi. We suggest seven of the nine most polymorphic VNTRs be used as a standardized typing scheme for epidemiological typing.