Evaluation of PFGE and MLVA in molecular typing of Salmonella Typhimurium isolated in China

Objective To compare the ability of pulse-field gel electrophoresis(PFGE) and two multiple loci VNTR analysis (MLVA) typing methods in molecular typing of Salmonella Typhimurium isolated in China and to obtain the valuable VNTR loci fit for S. Typhimurium molecular typing in China. Methods With the application of standard PFGE and MLVA including seven VNTR loci (MLVA_PN) protocols on PulseNet International network and MLVA protocol containing five VNTR loci (MLVA_EU) on European surveillance network, 175 isolates of S. Typhimurium from five provinces in China were typed. The molecular typing ability of the three methods were evaluated combined with the epidemiological information of the strains. Results The chromosomal DNA prepared from each S. Typhimurium strain was digested with XbaⅠrestricted endonucleotidase and 56 PFGE patterns were observed after pulse-field gel electrophoresis. The discrimination index (D) was 0.8823 for PFGE typing method. The predominant pattern of PFGE, JPXX01.CN0001of 55 S. Typhimurium isolates were further digested with the second enzyme BlnⅠto achieve additional 6 patterns. For MLVA_EU typing, it was showed 96 variant patterns and the D value reached 0.9758. For MLVA_PN method, 98 variant patterns were obtained and the D value was 0.9763, which indicated the discriminatory ability of the two MLVA typing methods for S. Typhimurium was similar. In addition, the typing results of 175 S. Typhimurium isolates by MLVA_EU were coincident with that by MLVA_PN. When S. Typhimurium strains isolated from patients and food in outbreaks were analyzed by PFGE with double enzymes digestion, MLVA_EU and MLVA_PN respectively, the results were coincident. Conclusion The discriminatory ability of the two MLVA typing methods were higher than that of PFGE. MLVA_EU containing five VNTR loci with the characterization of timesaving and easy manipulation is suitable for cluster analysis when detecting the outbreaks caused by S. Typhimurium in China.