| Salmonella can not only infect a variety of livestock and other animals,but also cause human food poisoning by contaminating various foods.It is an important zoonotic pathogen.More than 2,600 serotypes have been discovered to date,and Salmonella Corvallis is an important serotype in Salmonella.In the past,Salmonella Corvallis was rarely reported,and the serotype has been experiencing a trend of outbreaks in some countries such as Brazil,Japan,Bulgaria,Denmark and Tunisia in recent years.Studies have shown that Salmonella Corvallis has become a dominant serotype in poultry in Guangdong and Henan.However,there is still a systematic study on the resistance,scientific epidemiological characteristics and genetic evolution of Salmonella Corvallis,which will bring difficult to the prevention and control of this bacteria in China.Therefore,for the first time,Salmonella Corvallis were collected from different sources and regions（Guangdong,Guangxi,Shanghai,etc.）in this study,and its resistance,quinolones andβ-lactam resistance genes,virulence genes,plasmid incompatible groups,and biofilm formation ability were detected,and PFGE molecular typing was performed on these bacteria.The aim of this study is to understand the drug resistance,molecular epidemiology and genetic correlation of different sources of S.Corvallis in China,and provide basic data for clinical drug use and risk prediction control of this serotypes.In this study,205 strains of Salmonella Corvallis were isolated from Guangdong,Guangxi and Shanghai,including 114 humans（55.61%）and 91 food sources（44.39%）.The drug resistance test showed that the highest rate was sulfisoxazole（94.15%）,followed by tetracycline（77.56%）,florfenicol（48.29%）,and chloramphenicol（42.93%）.In addition,strains resistance to ciprofloxacin,cefotaxime,cefepime,imipenem,gentamicin and amikacin also were found.The drug resistance rates were 21.46%,2.44%,and 0.98%,0.49%,2.44%,and 1.95%,respectively.The resistance rates of ciprofloxacin and chloramphenicol in human strains were higher than those from food sources.It is worth noting that the multi-drug resistance rate has reached 63.9%,and the multi-drug resistance pattern has as many as 25,showing that the drug resistance is complicated.In this study,the drug resistance genes were detected in clinically important quinolones andβ-lactam drugs.The results showed that there were only par C（Thr57Ser）mutations（96.59%）in the quinolone resistance-determining region（QRDR）.In the plasmid-mediated quinolone resistance gene（PMQR）,the qnr S gene（85.85%）was ubiquitous,and qnr B（14.63%）and aac（6’）-Ib-cr（28.78%）genes were also found.The highest detection rate of bla TEM-1（18.05%）in the broad-spectrumβ-lactamase（ESBLs）gene,followed by bla CTX-M-55（4.88%）,bla TEM-116（1.95%）and bla OXA-1（1.46%）.In addition,the carbapenem resistance gene bla NDM-5（0.49%）was also detected.It is indicated that the clinically important drug-resistant S.Corvallis,which is mediated by drug resistance genes,has emerged in China and needs early prevention and control.The results of plasmid incompatibility group showed that a total of 45 strains were found to be incompatible,a total of 6 plasmid incompatibility group.mainly HI2（18.54%）,and N,Frep B,I1,A/C and Y were detected in small parts bacteria.Combining plasmid typing with drug resistance and drug resistance gene results showed that 94.74%（36/38）of the strains resistant to quinolones andβ-lactams in Salmonella carrying the Inc HI2 plasmid.65.79%（25/38）strains were resistant to ampicillin,nalidixic acid and ciprofloxacin.In the strain carrying the qnr B,aac（6’）-Ib-cr and bla TEM-1genes,the carrying rate of the Inc HI2plasmid could reach 90.00%,64.41%and 81.08%,respectively,suggesting that these genes may be located on the plasmid type and proceed propagation.The biofilm formation ability test showed that 95.61%of the strains could form biofilms,and 7.8%,14.15%and 73.66%of the strains had strong,medium and weak biofilm formation ability,respectively.Combined with drug resistance,streptomycin resistance of strains with strong biofilm formation ability was higher than that of moderate and weak,and strong and moderate florfenicol and chloramphenicol resistance were higher than weak ones.Virulence gene test results showed that 10 of the 15 virulence genes（sip A,sop E2,ssa B,ssr A,Mart,sii E,pip A,fim A,pef A and stn）were detected in all strains,indicating that these bacteria A large number of virulence genes are commonly carried.The homology of Salmonella was studied by pulsed-field gel electrophoresis（PFGE）.The results showed that the homology ranged from 40.11%to 100%,and the gene was clustered according to 85%homology.There are 15 gene clusters and 8 non-clustered genotypes,for a total of 74 genotypes.The dominant gene cluster is F cluster and the dominant genotype is D1.The genotypes of these bacteria generally showed genetic diversity,and it was also found that strains from different regions and different regions possess the same genotype.In addition,genotypes were found to be associated with drug-resistant phenotypes and biofilms.For example,75%（33/44）of ciprofloxacin-resistant strains were mainly concentrated in the K and L gene clusters,and57.58%（19/33）strains in the D cluster have medium or strong biofilm formation ability.In summary,this study is the first systematic epidemiological study of Salmonella Corvallis in different origins in China.It has been found that drug resistance is more serious and has higher multi-drug resistance rates,quinolones andβ-Amide-resistant genes may be transmitted through popular plasmid types and mediate drug resistance,and generally carry a large number of common virulence genes.In addition,almost all bacteria have biofilm formation ability,and most of them are multi-drug resistant bacteria.Molecular typing indicates that these bacteria are likely to spread in different regions and persist in these regions through clonal transmission and spread between humans and food.Prevention and control should be done as soon as possible to strengthen the monitoring of Salmonella Corvallis and use drugs rationally. |
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