| Salmonella spp,Escherichia coli 0157:H7,Listeria monocytohenes and Campylobacter jejuni are now the most important pathogens of foodborne diseases around the world.They not only can cause the animal and human's gastroenteritis,but also can cause the food poisoning of human beings,and even worse they can lead to deaths.The reports about food poisoning all over the world caused by the four pathogens are very common every year,which seriously hinder the sustainable development of our society and economy.The study here was carried out to continually investigate the prevalence of the four foodborne pathogens in the retail fresh meats in Nanning,and further to evaluate the pathogenicity and antimicrobial resistance of the Salmonella isolates.Totally 863 fresh meat samples including duck,chicken,beef and duck were randomly collected from 5 supermarkets and 4 wet markets in Nanning during July,2015 to November,2016.And the four foodborne pathogens were then detected according to the national standard method plus the supplemental PCR method developed in the laboratory.The serotypes of the 166 Salmonella isolates were assayed with the reference sera,and compared with the 159 Salmonella isolates of poultry on farms in the same period of time.The pathogenicity against Kunming mice of the dominant serotypes were evaluated,and 9 sets of PCR primers targeting the virulence genes were designed and used to detect.The drug resistance phenotypes against 16 common used antimicrobials of the 166 Salmonella isolates and 13 drug resistance genes were detected.Salmonella was the highest prevalent foodborne pathogens(19.24%,166/863)in the retail meats,then followed by E.coli 0157:H7(14.60%,126/863),C.j(8.92%,77/863)and Lm(0.81%,7/863).Further more,the contamination of Salmonella in samples from supermarkets(22.20%,93/419)was higher than that from wet markets(16.44%,73/444),and Lm was only detected in samples from supermarkets(1.43%,6/419)while comparing the results between supermarkets and wet markets.The comparisons of the results in different kinds of fresh meats showed that the percentages of pork samples positive for Salmonella and E.coli 0157:H7 and beef samples positive for Lm were higher than other kinds of meats,and a higher prevalence of C.j was found in meats of poultry than in livestock meats.An obvious difference was found in the prevalence of the four foodborne pathogens on different markets and at different seasons.The highest prevalence of Salmonella was detected in supermarket D and the highest prevalence of E.coli 0157:H7 and C.j were detected in wet market I,while Lm was only detected in supermarket E.A higher prevalence of Salmonella and E.coli O157:H7 was detected during summer and autumn than in other seasons and the highest prevalence of C.j was detected in summer,while the prevalence of Lm was very low in each month without seasonal difference.Totally nine serogroups including totally sixty-eight serovars were identified in the 166 Salmonella isolates obtained from the retail fresh meat samples,and the predominant serogroup was B and the predominant serovars were S.agona(15.06%),S.derby(15.06%),S.enteritidis(5.42%),S.riggil(4.82%),S.rissen(3.61%)and S.typhimurium(3.61%).Totally eight serogroups including thirty serovars were identified in the Salmonella isolates obtained from the retail chicken meat samples,while there were eight groups including totally twenty-six serovars among the Salmonella strains isolated from farm chicken samples.And the predominant serogroup was B and the predominant serovars were S.agona(15.91%),S.derby(9.09%),S.enteritidis(6.82%),S.men ston(6.82%),S.chartres(4.55%),while S.pullorum(75.47%),S.gallinarum(2.52%)were the predominant serovars in the poutry isolates even the predominant was also serogroup B.There were six serovars were detected in both retail chicken meat samples and farm chicken samples,e.g.S.agona,S.typhimurium,S.menston,S.braenderup,S.newlands,S.blegdam.The predominant serovars e.g.S.agona,S.derby,S.enteritidis,S.typhimurium,isolated from fresh meat samples,showed 40%-70%mortalities in the challenge test conducted to Kunming mice and that were associsted with the possess of sseL gene in Salmonella pathogenic island(SPI)-2 of the isolates.Antimicrobial susceptibility results indicated that 89.16%(148/166)of the Salmonella isolates displayed resistance phenotypes against the 16 antimicrobials to some extents.The highest incidence of resistance in Salmonella isolates was against TET(72.29%),then followed by AMP,CHL,AMC,TSU.Moreover,74.10%Salmonella isolates displayed multidrug resistance(MDR)against the 16 antimicrobials,and 55.42%of the Salmonella isolates displayed resistance to 2-7 antimicrobials,10.24%of them displayed resistance up to 10 or even 14 antimicrobials.The antimicrobial susceptibility analysis between the Salmonella isolates of retail chicken-meats and farm-chicken showed that the frequency of multidrug resistance of Salmonella isolated from chicken meats was much higher than that from farm chickens(67.44%vs 28.06%).In addition,there were 13.95%of chicken-meat Salmonella isolates displayed resistance to 10 or even more antimicrobials,while there were only 2.88%of farm-chicken.The drug resistance genes identified results showed that all genes against thirteen drugs including?-Lactams,sulfonamides,aminoglycosides and tetracycline were detected in the 166 Salmonella isolates.The coincidence between the phenotype and gene positive of drug resistance was 80.00%or more,and even was 96.70%on?-Lactams.The results of the study demonstrated that there were some extents of contamination of the four foodborne pathogens in the retail fresh meat products in Nanning,and that of Salmonella was the highest.The predominant serogroup of the Salmonella isolated from fresh meat was B,and the most predominant serovars were S.agona,S.derby,S.enteritidis,and S.typhimuriunm and they displayed high pathogenicity to Kunming mice.The status of drug resistance and multidrug resistance of the Salmonella isolates was serious. |
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