Molecular typing of Salmonella paratyphi A strains isolated in Hangzhou area from 2002 to 2013
Objective 
To analyze the molecular characteristics of Salmonella paratyphi A (S.paratyphi A) strains prevailing in Hangzhou area in recent years. 
 
 
Methods 
Pulse field gel electrophoresis (PFGE) and multiple-locus variable-number tandem repeat analysis (MLVA) were performed for molecular typing and epidemiological analysis of 72 S. paratyphi A strains isolated in Hangzhou area during 2002 to 2013. 
 
 
Results 
The 72 S. paratyphi A strains were divided into 11 PFGE (by using restriction enzymes of Xba Ⅰ and Bln Ⅰ) and 6 MLVA types. Among the selected 34 variable number tandem repeat (VNTR) sites, 4 sites (1188K, 2075K, 2201K and 4346K) showed high polymorphism, in which PFGE displayed a higher resolution than MLVA. Except for the 5 PFGE types of X4B5, X7B7, X8B8, X9B9 and X10B10, the other 6 PFGE types belonged to a same clone sharing a similarity of greater than 95%, and the S. Paratyphi A strains in that clone accounted for 93.1% of the total strains isolated in Hangzhou. 
 
 
Conclusion 
The occurrence of paratyphoid A in Hangzhou area from 2002 to 2013 was mainly caused by S. paratyphi A strains belonging to the same clone. Combination of PFGE with MLVA was conducive to epidemiological investigation of paratyphoid A. 
 
 
Key words: 
Salmonella paratyphi A; Pulse field gel electrophoresis; Multiple-locus variable-number tandem repeat analysis