Molecular characteristics of Salmonella typhi and Salmonella paratyphi A isolates in Hangzhou area

Abstract

Objective To determine the molecular characteristics of predominant Salmonella typhi and Salmonella paratyphi A strains prevalent in Hangzhou area from 2002 to 2008.Methods Pulse field gel electrophoresis (PFGE),multi-locus variable-number tandem repeat analysis (MLVA) and multi-locus sequence typing (MLST) were applied for typing as well as analysis of the molecular characteristics of 31 S.typhi isolates and 404 S.paratyphi A isolates from Hangzhou area during 2002 to 2008.Results The 404 S.paratyphi A isolates could be divided into six PFGE types (P1-P6).99.0％ of the S.paratyphi A isolates (400/404) belonged to the same one clone family (P1 and P2 types),in which P1 strains occupied 93.3％ (373/400) of the isolates.The 31 S.typhi isolates displayed a high diversity,which could be classified into 14 PFGE types,28 MLVA types with 90.3％ resolving power and 3 MLST types.The S.typhi strains prevalent in Hangzhou area were similar to those in Southeast Asia but different from those in Europe.The variable number tandem repeat (VNTR) sites with high polymorphism,TR1,TR2 and Sal02,could be used to the markers for diagnosis of S.typhi isolates in the area.The MLST types of 31 S.typhi isolates included all the three types currently found in the world but the ST2 type of S.typhi strains was predominant (23/31,74.2％).Conclusion The paratyphoid A prevalence in Hangzhou area in the recent years is caused by infection of the same clone family of S.paratyphi A whereas the S.typhi strains prevalent in the area display a high diversity. Key words: Salmonella typhi; Salmonella paratyphi A; Pulse field gel electrophoresis; Multi-locus variable-number tandem repeat analysis; Multi-locus sequence typing