Study On The Epidemic Characteristics And Antibiotic Resistance Of Salmonella Among Chicken And Pork Meats At The Farmer's Market In Guangdong

Salmonella is an important foodborne pathogen that can be transmitted to humans through animal and food chains,causing serious harm to human health and livestock and poultry production.It also has a great impact on public health security issues.Guangdong is an economically developed province in southern China.Its livestock production and consumption rank among the top in the country.The safety of livestock and poultry products is directly related to consumer health.However,the lack of data on the prevalence and resistance of Salmonella in chicken and pork meats in Guangdong farmers' market,which has brought great difficulties to the prevention and control of Salmonella in chicken and pork,and the prevention of Salmonellosis in humans.Therefore,this study aims to understand the prevalence of Salmonella in chicken and pork meat in Guangdong farmer's market,serotypes distribution,antimicrobial resistance,and ESBLs genotypes,providing guidance for the rational use of antibiotics in livestock and poultry breeding,and also provides a theoretical basis for the prevention and control of Salmonella.At the same time,the quinolone antibiotics and PFGE molecular typing in Salmonella common serotypes of chicken were studied,which provides the latest data for monitoring the prevalence of resistance genes and laying the foundation for the study of in-depth resistance mechanisms.Get the following main results:From 2016-2017,a total of 903 livestock and poultry meat samples(including 475 chicken and 428 pork)were collected from the retail markets in Guangdong(including Guangzhou,Shenzhen,Heyuan,Shaoguan,Foshan and Yunfu),and 615 strains of Salmonella were identified,the total isolated rate was 68.1%.Among them,302 were chicken(63.6% of isolates)and 313 were pork(73.1% of isolates).A total of 38 serotypes were identified in 615 strains of Salmonella,and the serotypes differed significantly between chicken and pork samples.27 serotypes were identified in chicken,the common serotypes were Agona(55 strains,18.2%),Corvallis(45 strains,14.9%),Kentucky(38 strains,12.6%)and Mbandaka(32 strains,10.6%);25 serotypes were identified in pork,common serotypes were Typhimurium(78 strains,24.9%),Rissen(67 strains,21.4%),Derby(66 strains,21.1%)and London(48,15.3%).The antibiotic susceptibility tests show that high antibiotic resistance rates were found in sulfisoxazole(76.1%),tetracycline(75.3%),ampicillin(48.0%),ofloxacin(44.7%).All Salmonella isolates were sensitive to cefepime(2.8%),ceftazidime(2.3%),amikacin(1.3%)and amoxicillin/clavulanic acid(1.1%).Of note,the "last-line" drugs polymyxin B(2.0%)and imipenem(0.5%),which are clinically used to treat bacterial infectious diseases have been detected.The multidrug resistance rate of the strain was 77.1%,and 61 different drug resistance spectra were obtained.The detection rate of multidrug resistance in Salmonella isolates(81.1%)was significantly higher than that in pork(73.2%)(P<0.05).The resistance rates of different serotypes of Salmonella differ greatly.ESBLs genotype detection revealed that bla OXA-1 was the dominant ESBLs gene(9/21,42.9%),followed by bla CTX-M-55(5/21,23.8%).This study examined the prevalence of quinolone-resistant QRDR mutations and the PMQR mediated by dominant serotype Salmonella in chicken,the results showed that the total detection rate of Salmonella PMQR gene in 138 strains was 83.3%.The detection rates of qnr S,aac(6')-Ib-cr,qnr B,qnr A,oqx AB,and qnr D were 71.0%,21.7%,18.1%,2.9%,1.4%,and 0.7%,respectively.The qnr S gene was the dominant PMQR detected by S.Agona and S.Corvallis;aac(6')-Ib-cr is the main S.Kentucky.40 amino acid mutation was detected in the QRDR genes of gyr A and par C in three serotypes of S.Corvallis,and S.Kentucky.Some mutations only exist in certain serotypes.For example,the Asp87 Tyr mutation in the gyr A gene only occurs in S.Corvallis;the mutations of Ser83 Phe and Asp87 Asn occurred in S.Kentucky;the Ser80 Ile mutation in the par C gene also occurs only in S.Kentucky.After PFGE typing of the same serotype strain,a total of 44 different PFGE genotypes were detected in 55 of S.Agona;34 different PFGE genotypes in 45 of S.Corvallis;38 of S.Kentucky exhibited 23 different PFGE genotypes.The PFGE results showed that the same serotype Salmonella isolated at different times and locations exhibited the same or different genotypes.The results of this study show that the chicken and pork of Salmonella contamination in Guangdong farmer's market is serious,the serotypes are complex and diverse,and antimicrobial resistance and multidrug resistance are very common.It is suggested that the food safety awareness of the management department and the production department should be enhanced,and the whole process of supervision and enforcement of food safety should be strengthened and strict control of antibiotic use.