Study On The Epidemiological Characters And Molecular Typing Of Salmonella In Zhejiang Province

OBJECTIVE:Salmonella is a typical pathogenic bacterium which causing human diarrhea and typhoid fever. The Reiter’s syndromes caused by Salmonella usually continue for a long time, which can lead to refractory chronic arthritis. Both of Bacterial food poisoning caused by salmonella outbreak and number of illness are ranked among the top in China for many years. And the infectious diarrhea caused by Salmonella belongs to category C infectious disease. This study focuses on understanding the epidemiological characters of Salmonella in Zhejiang, the serotypes, the antibiotic susceptibility, the distribution of virulence-associated genes and the molecular epidemiology in five regions of Zhejiang. All the results can help us to provide basis data for controlling the Salmonellosis.METHODS:A total of94Salmonella strains isolated from clinic specimens from five regions of Zhejiang province during2010-2012were collected and serotyped. K-B method was used to perform antibiotic susceptibility test and multiplex PCR was used to detect the 17virulence-associated genes (spvB、spiA、pagC、cdtB、msgA、invA、sipB、prgH、 spaN、orgA、tolC、iroN、sitC、lpfC、sifA、sopB、pefA) of Salmonella. The seven housekeeping genes of Salmonella were tested for multiple locus sequence typing (MLST).RESULTS:1. There were18various serovars out of94Salmonella isolates, which including29(30.85%) strains of Salmonella enteritidis,27(28.72%) strains of Salmonella typhimurium,10(10.64%) strains of Salmonella paratyphi,5(5.32%) strains of Salmonella newport and Salmonella irumu respectively,4(4.26%) strains of Salmonella cholerae,2(2.13%) strains of Salmonella typhi and Salmonella infantis respectively, and1(1.06%) strain of the rest of serovars respectively.53Salmonella strains were isolated from intestinal sources, including11various serovars with Salmonella typhimurium as the most one that accounting for47.17%, and41Salmonella strains were isolated from extraintestinal sources, including12various serovars with Salmonella enteritidis as the most one that accounting for31.71%.2. For the53Salmonella strains isolated from intestinal sources, ampicillin was the most resistant drug, while cefepime was the most sensitive one. Ampicillin was also the most resistant one for the41Salmonella strains isolated from extraintestinal sources in which no drug resistance of cephalosporin (CTX、CAZ、FEP) occurred.3. The virulence-associated genes spiA、pagC、msgA、sipB、prgH、spaN、tolC、 sitC、sifA and sopB were found in all strains. And invA(97.87%)、orgA(96.81%)、iroN (97.87%) and lpfC(87.23%)were found in most ones. While spvB(45.74%)、 cdtB(12.17%) and pefA(45.74%) in part ones. The virulence gene cdtB showed the lowest positive rate of12.77%, which was only found in Salmonella serotypes typhi and paratyphi. Meanwhile spvB and pefA were mainly in Salmonella serotypes enteritidis and typhimurium. cdtB was only found in the strains isolated from extraintestinal sources. And most of lpfC were found existed in the ones isolated from intestinal sources.4. The allele numbers of Salmonella housekeeping genes thrA、purE、sucA、hisD、 aroC^hemD and dnaN were divided into16、13、12、12、12、17and16kinds respectively.24STs among the94isolates were characterized by MLST, among which ST11accounted for29.79%as the most one, and ST19,ST85and ST34accounted for15.96%,10.64%and9.57%respectively. There were15STs in Salmonella strains isolated from intestinal sources and14ones in Salmonella strains isolated from extraintestinal sources. Five new STs(ST1746、ST1747、ST1748、ST1749and ST1750) were reported to the website of http://mlst.ucc.ie/mlst/.CONCLUSION:1. The main serovars among Salmonella strains clinically isolated from five regions of Zhejiang province were Salmonella enteritidis and Salmonella typhimurium.2. The antibiotic resistance was not very serious in the experimental strains.3. The chromosomal virulence-associated genes except cdtB were widely distributed in these strains.SpvB and pefA which encoded by virulence plasmids were detected with high positive rate.4. MLST was generally associated with serotype.