Multiple locus sequence typing of Salmonella Typhi, isolated in north India - a preliminary study

BACKGROUND & OBJECTIVES: In India enteric fever is a major public health problem and Salmonella Typhi is the most common aetiologic agent. Any control strategy for such infections depends to a large extent on the understanding of the disease and relatedness of strains across the world. Multi locus sequence typing (MLST) is one such method of genotyping of bacteria based upon housekeeping genes of known function and chromosome position. MLST data of pathogens are important to determine the molecular evolution by a stable and reproducible method. This study was undertaken to determine the sequence types of representatives S. Typhi isolates obtained from enteric fever patients in a tertiary care centre in north India, over a period of 20 years (1990-2010). METHODS: A total of 30 representative isolates of S. Typhi identified by biochemical and serological tests were subjected to multi locus sequence typing (MLST). Seven housekeeping genes of known function and chromosome position were used for the typing by MLST. Sequencing was carried out by using an automated DNA sequencer and results were analyzed to generate phylogenetic tree. RESULTS: MLST pattern grouped S. Typhi into two sequence types- ST1 and ST2. ST1 was predominantly present followed by ST2. INTERPRETATION & CONCLUSIONS: By MLST the presence of both sequence types, ST1 and ST2, was found in S. Typhi isolates in our region. Predominately ST1 was present followed by ST2. These preliminary results corroborate the global distribution of both sequence types of S. Typhi and also emphasize for the continuous screening of S. Typhi.