Resistance And Molecular Characterization Of Resistance Genes In Salmonella Enteritis

Salmonella is an important zoonotic and food borne pathogen,and also an important food borne pathogens,which causes human diarrhea and even food poisoning through the pollution of animal food,whom usually need antibiotic treatment.Salmonella Enteritidis is one of the most common non-typhoid serotypes of foodborne infection in China.Salmonella resistance becomes more complex with the widespread use of antibiotics and multi-drug resistance is concerned.ACSSuT is a multidrug-resistant phenotype that is of concern to Salmonella non-Typhoid but rarely is reported in Salmonella Enteritidis.Therefore,it is necessary to investigate the drug resistance and multidrug resistance of Salmonella Enteritidis.Salmonella Enteritidiswere collected in Shanghai and the antimicrob ial susceptibility of 16 drugs were tested.The results showed that the higher resistance rate of Salmonella enteritidis was nalidixic acid(95.29%),ampicillin(62.22%),sulfa(8.3%),cefepime(8.34%),cefotaxime(7.05%),ciprofloxacin(10.4%),cefotaxime(3.18%),ofloxacin(0.52%)respectively,and all of them were sensitive to imipenem.A total of 110 strains of Salmonella Enteritidis with ACSSuT were selected.The results showed that all the drug-resistant strains carried the corresponding drug resistance genes and the higher frequency of resistance genes was sul2(74.55%),flo(67.27%),blaCTX-M(60.00%),tet A(49.09%),aph(3')-IIa(46.36%),mediated resistance of sulfonamides,chloramphenicol,cephalosporins,tetracycline,and aminoglyco-side respectively.21 virulence genes were tested in 110 isolates,the results indicated that Mar,siiE,Pipa,sopE2,spv C,spv R,pef A,prot6 E,Rck,fim A,lpf D,sseI were widespread in the multi-drug resistant SalmonellaEnteritidis.All of strains carried14-19 virulence genes,suggesting that multidrug-resistant enteritis had high virulence and high potential of prevalence.ACSSuT strains had an increased resistance to other tested drugs except for imipenem.For cefotaxime,cefotaxime and cefepime,the rates were 70.64%,48.62% and 58.72%,respectively.Usually ESBLS strains are resistant to both three generations of cephalosporins and aztreonam.In this study,60.9% of the strains were found to be ESBLS phenotype-positive strains.The prevalence of extended-spectrum beta-lactamases(ESBLS)genes showed thatCTX-M was the predominant gene,and CTX-M-55 subtypes account for 96%.The results showed that five(4.54%)strains carrying theclass 1 integron gene cassette.The most common integrin cassette was aadA2-dfrA12,indicating that class 1 integron played an important role in the spread of aminoglycosides and sulfonamides drug resistance genes in multi-drug resistant Salmonella Enteritidis.ESBLS genes were not detected in class 1 integron cassette indicating that the emergence and prevalence of co-resistance to ACSS uT and cephalosporins strains was not mediated by the integrin,and CTX-M-55 was closely related to the drug resistance to the third-generations cephalosporins andother mobile DNA elements may be involved too.The resistance rate of ciprofloxacin(9.09% VS3.18%)and ofloxacin(4.59% VS 0.52%)were slightly higher than that of the whole ACSSuT strain.In this study,the QRDR mutation and five pairs of PMQR were detected.The results showed that 93% of the strains had mutations and only gyrA single mutations were present,of which the proportion of 87 mutations were more than 90%,and single mutation mainly mediated resistance to nalidixic acid.Qnr B was the most prevalent plasmid-mediated genes,the detection rate of PMQ R was qnrB(10.91%)and aac(6')-Ib-cr(8.18%).Compared with QRDR single mutant,ciprofloxacin reduced sensitivity in the isolates with mutations in gyrA and presence of PMQR and qnr B had a greater effect on ciprofloxacin than aac(6')-Ib-cr,which can be reduced to a greater extent to the sensitivity of the strain to ciprofloxacin.PFGE typing method was used to study the homology of Salmonellaenteritidis,and the diffusion mechanism of drug resistance gene was discussed.PFGE typing showed that 109 strains were successfully classified.66 strains of CTX-M positive strains were divided into 24 genotypes.Among them,26 strains were sharing the same PFGE type,and these strains were positive for CTX-M-55.The other strains showed diversity in the PFGE type.The results showed that the prevalence of CTX-M-55 was not only related to the distribution of clonal propagation,but also by the plasmid and other mobile components caused by the horizontal transfer together.The special mechanism of transmission needs to be further exploied.