The molecular epidemiological characteristics and genetic diversity of salmonella typhimurium in Guangdong, China, 2007-2011.
BACKGROUND
Salmonella enterica serovar Typhimurium is the most important serovar associated with human salmonellosis worldwide. Here we aimed to explore the molecular epidemiology and genetic characteristics of this serovar in Guangdong, China.


METHODS
We evaluated the molecular epidemiology and genetic characteristics of 294 endemic Salmonella Typhimurium clinical isolates which were collected from 1977 to 2011 in Guangdong, China, and compared them with a global set of isolates of this serovar using epidemiological data and Multilocus Sequence Typing (MLST) analysis.


RESULTS
The 294 isolates were assigned to 13 Sequencing types (STs) by MLST, of which ST34 and ST19 were the most common in Guangdong. All the STs were further assigned to two eBurst Groups, eBG1 and eBG138. The eBG1 was the major group endemic in Guangdong. Nucleotide and amino acid variability were comparable for all seven MLST loci. Tajima's D test suggested positive selection in hisD and thrA genes (p<0.01), but positive selection was rejected for the five other genes (p>0.05). In addition, The Tajima's D test within each eBG using the global set of isolates showed positive selection in eBG1 and eBG138 (p<0.05), but was rejected in eBG243 (p>0.05). We also analyzed the phylogenetic structure of Salmonella Typhimurium from worldwide sources and found that certain STs are geographically restricted. ACSSuT was the predominant multidrug resistance pattern for this serovar. The resistant profiles ACSSuTTmNaG, ACSSuTTmNa and ACSuTTmNaG seem to be specific for ST34, and ASSuTNa for ST19.


CONCLUSIONS
Here we presented a genotypic characterization of Salmonella Typhimurium isolates using MLST and found two major STs are endemic in Guangdong. Our analyses indicate that genetic selection may have shaped the Salmonella Typhimurium populations. However, further evaluation with additional isolates from various sources will be essential to reveal the scope of the epidemiological characteristics of Salmonella Typhimurium in Guangdong, China.
Guangdong Provincial Institute of Public Health, Guangdong Provincial Center for Disease Control and Prevention, Guangzhou, China.
Jiufeng
J
Sun
Institute of Microbiology, Guangdong Provincial Center for Disease Control and Prevention, Guangzhou, China.
Bixia
B
Ke
Department of Epidemiology, School of Public Health and Tropical Medicine, Southern Medical University, Guangzhou, China.
Yanhui
Y
Huang
Institute of Microbiology, Guangdong Provincial Center for Disease Control and Prevention, Guangzhou, China.
Dongmei
D
He
Institute of Microbiology, Guangdong Provincial Center for Disease Control and Prevention, Guangzhou, China.
Xiaocui
X
Li
Institute of Microbiology, Guangdong Provincial Center for Disease Control and Prevention, Guangzhou, China.
Zhaoming
Z
Liang
Institute of Microbiology, Guangdong Provincial Center for Disease Control and Prevention, Guangzhou, China.
Changwen
C
Ke
D000900:Anti-Bacterial Agents / Q000494:pharmacology; D044466:Asian People; D002681:China / Q000453:epidemiology; D004269:DNA, Bacterial / Q000737:chemistry / Q000235:genetics; D019353:Endemic Diseases; D014644:Genetic Variation; D005838:Genotype; D005843:Geography; D006801:Humans; D008826:Microbial Sensitivity Tests; D017720:Molecular Epidemiology; D058885:Multilocus Sequence Typing / Q000379:methods; D010802:Phylogeny; D012480:Salmonella Infections / Q000453:epidemiology* / Q000208:ethnology / Q000382:microbiology; D012486:Salmonella typhimurium / Q000145:classification / Q000187:drug effects / Q000235:genetics*; D017422:Sequence Analysis, DNA; D012703:Serotyping / Q000379:methods
D000900:Anti-Bacterial Agents; D004269:DNA, Bacterial