| Listeria monocytogenes(Lm),an important zoonotic foodborne pathogen,can infect humans and more than 60 animal species with a fatality rate of 20%-30%.Listeriosis is mainly caused by eating food contaminated with Lm.Lm can be detected in raw meat such as chicken,pork and mutton,which are higher than other foods.So that it poses a serious threat to the health of consumers.In China,most cases of listeriosis are sporadic,and ST9,ST8 and ST87 are the frequent STs in clinical isolates.In recent years,the production and consumption of chicken have been tremendously increasing in China.Lm can transmit through the chain of chicken production,which poses potential risks to human health.Therefore,it is essential to clarify the epidemiological characterization of Lm in the slaughtering and marketing links.However,there is a paucity of information on the distribution of Lm through the chain of chicken production.This study investigated the contamination characteristics of Lm in the slaughtering and marketing links.The genetic evolution relationship of isolates was studied via comparative genomics analysis of MLST,cgMLST and SNP.Moreover,we compared the distribution of virulence genes and antibiotic-resistant genes of isolates,which would provide a theoretical basis for effectively controlling the pollution and transmission of Lm in chicken.The pollution of Lm in retail chicken meat is severe.The establishment and application of efficient food sterilization technology is beneficial to control the pollution of Lm.It is beneficial to control Lm by establishing and applying green and efficient food sterilization technology.UV-C radiation has advantages of simple operation,high efficiency and rapidity.UV-C technology as new methods for sterilizing food has caught the attention of the food industry.In this study,we explored the inactivation effect of UV-C radiation on Lm and the effect on the quality of chicken meat,providing a scientific foundation for controlling the pollution of Lm by UV-C radiation.1.Investigation of Lm transmission in chicken slaughter chainA total of 200 samples were collected from the chicken slaughterhouse with the positive rate of 20.0%.There was a higher prevalence in the process of precooling and segmentation,indicating they were critical control points in chicken slaughter chain.40 isolates of Lm were serotyped into three serotypes(1/2 a,1/2b and 1/2c),among which the dominant serotype was 1/2c(47.5%).All isolates represented 8 sequence types,among which the dominant STs were ST9(40.0%),ST87(20.0%)and ST8(10.0%).All strains carried Listeria pathogenicity island 1(LIPI-1)and internalin genes inIA,inlB,inlC and inlH.In addition,ST330 strains carried Listeria pathogenicity island 3(LIPI-3),and ST87 strains harbored Listeria pathogenicity island 4(LIPI-4).These results showed that Lm derived from the chicken slaughterhouse has potential pathogenic risks to consumers.SNP cluster analysis showed that there was a closely genetic relationship between isolates from environmental samples in the same link at different times,indicating that Lm might persist in the slaughterhouse environment.Between strains from the same branch isolated from different sources which showed high genetic similarity,indicating that the cross-contamination existed between broiler carcasses and the environment.2.Molecular subtyping of Lm from retail chicken meatA total of 542 samples were collected from chicken samples with the positive rate of 31.4%.Among them,a total of 299 samples from three supermarkets in Yangzhou with the positive rate of 32.8%;The Lm positive rate of supermarket C was higher than that of supermarket A and B;It suggested that the Lm positive rate fluctuated with month and no seasonal variation;The presence of Lm in chilled chicken was higher than that of frozen chicken and cooked chicken.170 isolates of Lm were subtyped into four serotypes(1/2 a,1/2b,1/2c and 4b),among which the predominant serotype was 1/2a(47.1%).All isolates were classified into 16 STs,among which the dominant STs were ST9(34.7%),ST8(20.0%)and ST87(10.0%).There was an allelic difference among some STs,forming three clonal complexes of CC9,CC7 and CC155.85.9%of isolates carried complete LIPI-1.LIPI-3 was distributed in ST288 isolates,and ST87 isolates harbored LIPI-4.All isolates carried 2-6 antibiotic-resistance genes.ST155 and ST705 strains harbored more than 4 antibiotic-resistance genes.59 isolates(34.7%)of Lm harbored a complete CRISPR-Cas system.The CRISPR-Cas system of Lm isolates was divided into two types,type?B and type?A.Interestingly,all ST121 isolates carried two CRISPR-Cas systems,type?B and type?A.Core genome multilocus sequence typing(cgMLST)classified the 170 isolates into 13 CCs,and CC288,CC429 and CC87 presented a closely phylogenetic relationship.There was a closely relationship between isolates from different supermarkets in Yangzhou,which were supplied by the same slaughterhouse,indicating that part of Lm strains in retail chicken meat originated from the slaughter link.Additionally,some isolates showed high genetic similarity to clinical isolates,suggesting that Lm in retail chicken meat had potential pathogenic risks to cause listeriosis.3.Effect of UV-C irradiation on the inactivation of Lm and the quality of chicken meatTo evaluate the effect of UV-C irradiation on the inactivation of Lm,BHI plates were inoculated with different serotypes Lm and then irradiated with UV-C light.Microbiological data indicated that the population of Lm with UV-C dose at 6 J/m2 was significantly lower than that of the control group.Meanwhile,there was no significant difference among the sensitivity of different serotypes of Lm.Chicken breasts were inoculated with Lm and irradiated with UV-C dose of 50,100,200 and 400 mJ/cm2.Microbiological data indicated that the population of Lm decreased significantly with increasing UV-C dose.The main evaluation indexes of sensory quality included Hunter color values,thiobarbituric acid reactive substances(TBARS)value and pH value.Our results indicated that there were no significant differences in Hunter L*,a*,and b*values between all doses and the control group.The TBARS value of the chicken breasts slowly increased with increasing UV-C dose,while there was no significant difference among 50,100 mJ/cm2 and the control group.Compared with the control group,400 mJ/cm2 of irradiation significantly increased pH value,while there was no significant difference with other doses.In order to achieve the best sterilization efficacy with minimal effects on chicken quality,the irradiation dose was chosen as 100 mJ/cm2.Compared with the control group,100 mJ/cm2 of irradiation significantly decreased the population of Lm during storage,indicating that growth of Lm was affected by UV-C irradiation during storage at 4?.In this study,we evaluated the epidemiological characteristics of Lm from the slaughter and sale links.Lm might persist in the chicken slaughterhouse environment and occur cross-contamination between broiler carcasses and the environment.Lm contamination of retail chicken meat was severe,and some Lm isolates showed high genetic similarity to clinical isolates,suggesting that Lm in retail chicken meat had potential risks to cause listeriosis.Besides,the results indicated that optimized UV-C irradiation decreased the population of Lm inoculated in the chicken without impairing quality.Additionally,the growth of Lm was also affected by UV-C radiation during storage at 4?.This study provided a new insight for the control of Lm and the prevention of listeriosis. |
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