| In this study, a total of 391 samples were collected from retail market in Guangdong province, as a result 279 Salmonella strains were obtained, and the isolation rate of Salmonella in these samples was 71.34%. And a total of 26(9.32%) Salmonella Derby isolates were obtained in all Salmonella isolates. On the other hand, 133 Salmonella Derby isolates were collected from Shanghai, contains 74 human source strains and 59 food source strains. A total of 159 isolates of Salmonella Derby were used in this study.In this study, 159 Salmonella Derby isolates were tested for the antimicrobial susceptibility test of 16 antibiotics, and the results indicated that isolates displayed a high-level and wide spectrum of antibiotic resistance, 98.11%(156/159) Salmonella Derby isolates was resistant to at least one antimicrobial, the highest frequency of resistance was to tetracycline(88.05%) and sulfamethoxazole(78.62%) and streptomycin(58.49%). Different sources and different regions of the Salmonella Derby isolates on the drug resistance exists differences: the streptomycin resistance of Salmonella Derby isolates from food source was significantly higher than the streptomycin resistance of Salmonella Derby isolates from human source; the sulfamethoxazole resistance of Salmonella Derby isolates in Guangdong Province was 100%, which was significantly higher than that in Shanghai. Multiple drug resistance statistics results indicated that Salmonella Derby isolates contain 50 resistance patterns, 69.81%(111/159) isolates were resistant to ≥3 antimicrobials, and exist isolates with a thirteen-drug-resistance pattern.In this study, 159 Salmonella Derby isolates were tested for 10 virulence genes, and the results indicated that the virulence gene avr A(100%), bcf C(100%), ssa Q(99.37%), sii D(98.74%), mgt C(98.11%), sop B(98.11%), sop E(96.86%), sod C1(95.60%), gip A(4.40%) and spv C(0.63%) were present in flock, and the predominant virulence gene pattern was "avr A-ssa Q-mgt C-sii D-sop B-sod C1-sop E-bcf C"(84.91%, 135/159) in flock. The types of virulence gene of Shanghai Salmonella Derby isolates were more than that of the Guangdong Salmonella Derby isolates, it suggested the pathogenicity of Salmonella Derby in Shanghai was higher than that in Guangdong.In this study, 159 Salmonella Derby isolates were tested for 18 plasmid incompatibility groups, and the results indicated that 11 plasmid incompatibility groups were present in flock. The highest frequency of plasmid incompatibility groups that harbored by flock were FIA(50.94%), P(33.33%) and FIC(28.30%). In plasmid incompatibility groups profiles, 82.39%(131/159) Salmonella Derby isolates harbored the plasmid incompatibility groups, and there was no obvious predominant plasmid incompatibility groups patterns, the number of plasmid incompatibility group harbored by one strain reach the maximum of 6. Different sources and different regions of the Salmonella Derby isolates harbored plasmid incompatibility groups exist differences:plasmid incompatibility groups HI1, HI2 and P harbored rate in different sources of Salmonella Derby isolates flock were significantly different, plasmid incompatibility groups T, FIB and Frep B harbored rate in different regions of the Salmonella Derby isolates flock in the different regions is significant, plasmid incompatibility groups Y and FIIs only exist in the Salmonella Derby isolates flock in Shanghai.The Salmonella Derby isolates were digested with restriction endonuclease Xba I and analyzed using PFGE, the rate was 94.97%(151/159), contain 84 PFGE pattern, the range of similarities of PFGE pattern was 65%-100%. The isolates grouped into 11 clusters with 85% pattern similarity, the statistics results showed that the isolates from different sources, different time of isolation and different regions of isolation were grouped together in a cluster, moreover in some cases shared identical patterns. The results suggested that the Salmonella Derby strain has potential cross-contamination between different sources, time and geographic regions.In this study, there was association between virulence genes and similarity of strain, between plasmid incompatibility groups and similarity of strain. In addition, there was association between certain PFGE molecular typing and virulence gene profiles, certain PFGE molecular typing and plasmid incompatibility groups profiles, suggesting virulence subtyping and plasmid incompatibility groups subtyping can be useful typing tools to discriminate isolates in different requirements.Salmonella Derby as a common serotype of Salmonella enterica, ranks among the top five of the isolation rate in in the various researches.However, the related researches on Salmonella Derby is very limited, as a result the resistance, pathogenicity and plasmid carrying status of Salmonella Derby is not clear so far. In this study, Salmonella Derby recovered from different sources and different regions was characterized for antimicrobial susceptibility, virulence genes, plasmid incompatibility groups and molecular subtypes using pulsed field gel electrophoresis, and investigated the molecular characterization and antimicrobial resistance of Salmonella Derby. |
