| Salmonella is a kind of the most common food-borne pathogen,which spread mainly through the animal foodstuff,and caused human food poisoning incidents almost every year on a global scale.Recent studies show that the drug resistance of Salmonella has increased year by year,which undoubtedly presented a serious impact on the clinical efficacy of antimicrobials.Therefore,it is of important significance to do related research on Salmonella in animal food sources.In our study,we investigated the pollution of Salmonella in the production chian of a large-scale duck abattoir in Sichuan province,and serotype,antimicrobial susceptibility test,virulence genes detected,PFGE typing analysis were performed among the Salmonella isolates.1 Isolation and identification of Salmonella isolates from duck slaughter chainA total of 523 samples from the duck slaughter chain were collected during May 2016 to July 2017,include pre-slaughter,post-depilation,post-evisceration,post-segmentation and pre-cooling samples.Salmonella were isolated in accordance with GB 4789.4-2010 and further identified by using dual PCR method.The results displayed that 143 samples were contaminated with Salmonella,with a total pollution rate of 27.3%,and 156 Salmonella isolates were recovered from these samples.The contamination rates of the samples in different slaughter links were 43.5%,27.0%,24.8%,24.4%,18.3%,and in different times were 33.3%,15.6%,31.7%,respectively.A total of 11 distinct serotypes were generated among the 156 Salmonella isolates,mainly in S.Indiana(n=41),S.Newlands(n=29)and S.Newport(n=27).The distribution and prevalence of serotypes in different slaughter links and sampling times showed a big difference.2 Analysis of antibiotic resistance of Salmonella isolates from duck slaughter chainKirby-Bauer disk diffusion method was performed to detect the susceptibility of 156 Salmonella isolates against 10 antimicrobial agents.The results indicated that the resistance of the 156 Salmonella isolates was most frequently observed resistant to nalidixic acid(94.2%),followed by ampicillin(59.6%),tetracycline(51.3%)and trimethoprim-sulfamethoxazole(46.2%).Less resistance was detected to ciprofloxacin(27.6%),ceftriaxone(25.6%),minocycline(20.5%),kanamycin(19.2%),amoxicillin-clavulanic acid(14.7%)and gentamycin(14.1%).98.1% of the isolates were resistant to at least one antimicrobial agent,while 63.5% presented multi-drug resistance,and 50 different resistance patterns were displayed among the isolates.3 Detection of virulence genes of Salmonella isolates from duck slaughter chainVirulence genes which located in Salmonella pathogenicity islands(SPI),fimbrial,plasmid and prophage were detected among the isolates by PCR method.The results suggested that the carriage rate of Salmonella isolates on tested SPI,fimbrial virulence genes and plasmid virulence gene spvR was over 80.0%,followed by plasmid virulence gene spv B(26.9%)and spvC(10.9%).No Salmonella isolate detected carrying plasmid virulence gene pefA and prophage virulence gene sopE.97.4% of the isolates carried at least one tested SPI virulence gene,while 91.0% carried 5 and more tested virulence genes simultaneously.A total of 30 kinds of virulence gene profiles were found.The differences in the distribution of virulence genes were mainly reflected in the serotypes,in which S.Typhimurium had a rate of 100.0% for all tested virulence genes except pefA and sopE.4 PFGE typing of Salmonella isolates from duck slaughter chainXba I and the protocol developed by CDC were adopted for 108 representative Salmonella isolates PFGE typing.It turned out that 8 isolates couldn't be typed by PFGE,and the PFGE fingerprinting profiles similarity of the rest 100 isolates were between 33.81% and 99.09%,which generated 41 different PFGE types.There was a certain correlation between PFGE type and Salmonella serogroup,but no relationship was found of that with resistance pattern or virulence gene profile.Besides,the PFGE types indicated that Salmonella could be spread along the slaughter chain and cross-contamination was existed;Exogenous Salmonella may transmit into the slaughter chain through different slaughter links;Part of the Salmonella strains could survive in the farms or slaughter chain for a long time and spread to the slaughtering objects.In this paper,a systematic investigation and analysis of Salmonella which recovered from duck slaughter chain was carried out.The results of separation identification and antimicrobials susceptibility test provided a data support for the monitoring of Salmonella pollution in ducks and the changes of their antibiotic resistance;The results of the virulence gene detection provided a reference for assessing the potential risk of Salmonella in duck slaughter chain;At last,the PFGE typing results provided the theoretical basis for studying the spread of Salmonella in duck slaughter chain. |
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