Abstract:Objective To evaluate the antimicrobial resistance characteristics and molecular epidemiological features of Escherichia coli in retail whole chickens in Beijing， including resistance rates， resistance profiles， serotypes， sequence types （STs）， major resistance genes and plasmids distribution.Methods From December 2017 to March 2023， Escherichia coli was isolated from whole chickens， and was subjected for antimicrobial susceptibility testing. Cefotaxime （CTX）-resistant isolates were selected for whole-genome sequencing， and bioinformatics methods were used to analyze the genomic characteristics of the isolates.Results The prevalence of Escherichia coli in 87 retailed whole chickens samples was 87.4%， of which 84.2% of the strains showed varying degrees of resistance against detected antibiotics， with tetracycline （76.2%） as the most resistant antibiotic， and 71.8% of the strains were multidrug resistant. Genomic analysis of 38 CTX-resistant isolates showed that they belonged with 28 serotypes and 29 STs， and core genome multi-locus sequence typing （cgMLST） revealed even higher genetic diversity. The dominant antimicrobial resistance genes were the ESBL-encoding gene bla_CTX-M-65 （44.7%， 17/38） for β-lactam resistance， the plasmid-mediated qnrS1 （60.0%， 18/30） and chromosomal mutation GyrA_S83L （96.7%， 29/30） for quinolones resistance. Additionally， 78.9% of the strains exhibited co-resistance to third-generation cephalosporins and quinolones. Plasmid analysis indicated that the IncFIB plasmid type was the most prevalent （81.6%， 31/38）.Conclusion The contamination of multidrug resistant Escherichia coli in retail whole chickens in Beijing City was high. These strains carried multiple resistance genes， posing a potential risk of plasmid-mediated horizontal gene transfer. These findings highlight the need to strengthen food safety regulation and antibiotic usage supervision.

Abstract:Objective To perform molecular typing and traceability analysis on samples from a food poisoning incident caused by Staphylococcus aureus at a school in Boluo County， Huizhou City， and to provide guidance for future management and judgment of similiar epidemic events.Methods Suspected samples were collected， and Staphylococcus aureus was identified using a VITEK MS mass spectrometer. Enzyme-linked immunosorbent assay （ELISA） was used to detect enterotoxin types. Whole-genome sequencing （WGS） was employed to identify resistance and virulence genes， and to perform multilocus sequence typing （MLST） and whole-genome single-nucleotide polymorphism （wgSNP） analysis. A phylogenetic tree was constructed to trace the origin of the pathogen.Results A total of 10 Staphylococcus aureus strains were isolated， including 6 from anal swabs， 3 from vomitus， and 1 from chicken steak. ELISA testing revealed that 8 patient-derived strains and 1 food-derived strain produced type A enterotoxin， while 1 patient-derived strain produced type B enterotoxin. The 9 strains producing type A enterotoxin were all ST6， and the 1 strain producing type B enterotoxin was ST338. The ST6 strains carried multiple resistance genes， and all harbored the enterotoxin A gene （sea） and several hemolysin genes. The ST338 strain carried the enterotoxin B gene （seb）. Phylogenetic analysis showed that the ST6 patient-derived strains and the food-derived strain belonged to the same cluster， with SNP differences ranging from 0 to 14.Conclusion This food poisoning incident was caused by ST6 S. aureus contaminating the chicken steak. This study provides important data support for the prevention and control of foodborne diseases.

Abstract:Objective To establish a method for the determination of polychlorinated naphthalenes in bivalve molluscs by gas chromatography-triple quadrupole mass spectrometry （GC-MS/MS）.Methods The samples were dehydrated with anhydrous Na₂SO₄， extracted by accelerated solvent extraction， and purified by Captiva EMR-Lipid and alkaline alumina solid phase extraction column. The analytes were separated on SH-I-5Sil MS column， analyzed by GC-MS/MS in multiple reaction monitoring mode （MRM） and quantified by external standard method.Results The correlation coefficients （r） of eight polychlorinated naphthalenes were above 0.998 in the range of 1~100 μg/L. The detection limits and quantitative limits were in the range of 6.5~14.7 pg/g and 21.8~49.1 pg/g， respectively. The recoveries ranged from 77.5%~112.2%， and the relative standard deviation were 0.9%~7.9%.Conclusion The method is accurate and reproducible， making it suitable for the quantification of polychlorinated naphthalenes in bivalve molluscs.

Abstract:Objective To investigate the contamination status of Listeria monocytogenes in frozen prepared dishes collected from Huzhou City during 2023—2024， and to elucidate the antimicrobial resistance and genetic characteristics of the isolates.Methods A total of 127 retail frozen prepared dish samples were randomly collected in Huzhou City from 2023 to 2024. L. monocytogenes was isolated and identified according to the China national food safety standard GB 4789.30—2016. Minimum inhibitory concentrations （MICs） for 8 antibiotics were determined for 21 L. monocytogenes isolates using the broth microdilution method. Whole genome sequencing and bioinformatics analysis were conducted to analyze isolates lineages， serotypes， sequence types （STs）， clonal complexes （CCs）， core genome multi locus sequence types （cgMLSTs）， resistance genes， virulence genes， and stress response genes.Results L. monocytogenes was detected in 21 of 127 samples， with an overall detection rate of 16.54% （21/127）. Serotype 1/2a was dominant， accounting for 57.14% （12/21） of all isolates. The 21 isolates belonged to two lineages （Lineage Ⅰ and Ⅱ）， and were classified into 7 CCs and 7 STs. The predominant CC-ST types were CC121-ST121 （28.57%）， CC8-ST8 （23.81%）， and CC87-ST87 （19.05%）. All isolates carried the LIPI-1 pathogenicity island and key internalin family virulence genes such as inlA， inlB， and inlC. Premature stop codon （PMSC） mutations in inlA were observed exclusively in Lineage Ⅱ strains. One CC288-ST330 strain carried LIPI-3 associated virulence genes， and all CC87-ST87 strains carried LIPI-4， indicating more pathogenic potentiality. Strains of ST5， ST8， ST9， and ST155 carried stress survival island 1 （SSI-1） genes. In total， 95.24% （20/21） of isolates were sensitive to the tested antibiotics， while one isolate showed resistance to both the first-line antibiotic penicillin （PEN） and the broad-spectrum antibiotic meropenem （MEM）. cgMLST phylogenetic analysis revealed close evolutionary relationships among strains isolated from samples with the same manufacturer， and a possible persistence of ST8 strains was observed across two consecutive years in one production facility， suggesting ongoing contamination existed.Conclusion A certain level of L. monocytogenes contamination existed in frozen prepared dishes in Huzhou City， with particular concern for high-virulence ST87 strains and occasional antibiotic resistance. These findings highlight the need for food production enterprises to strengthen raw material control and process management， while also promoting consumer awareness of food safety during handling and cooking of prepared dishes to reduce potential health risks.

Abstract:Objective To investigate the distribution characteristics of Vibrio parahaemolyticus from different aquatic product sources in Jiangsu Province from 2019 to 2021， and to analyze the differences in genomic characteristics and antimicrobial resistance.Methods This study analyzed the temporal and source-specific distribution of Vibrio parahaemolyticus that was detected from 838 aquatic product samples （collected between 2019 and 2021） using the method outlined in GB 4789.7—2013. Whole-genome sequencing （WGS） and antimicrobial susceptibility testing were conducted on 55 successfully revived Vibrio parahaemolyticus strains. Bioinformatics analyses were employed for phylogenetic construction， virulence and resistance gene screening， and serotype predicting， from which serotypes were validated using traditional serum agglutination method.Results A total of 92 Vibrio parahaemolyticus strains were detected， with a detection rate of 10.98%， showing no statistically significant difference among different food sources （χ2=0.44， P=0.801）. Among the 55 sequenced strains， 34 strains were classified into 33 sequence types （STs）， while STs of 21 strains were unknown. The predominant serotype in seafood isolates was O5：K17 （18.52%）， while O2：K22 （26.32%） was predominant in freshwater product isolates. Derivative serotypes O5：K17 and O1：K25 of the pandemic serotype O3：K6 were detected in both seafood and freshwater product isolates. None of the strains carried the tdh gene， while only two seafood isolates harbored trh， along with hlyB and hlyC genes. All strains were resistant to cefazolin. Quinolone resistance genes qnrC and qnrS5 were detected exclusively in one freshwater product isolate.Conclusion Vibrio parahaemolyticus in Jiangsu province demonstrated diverse distributions in both STs and serotypes. The primary risk associated with seafood lies in the combinations of predominant pandemic lineages and the presence of specific virulence gene， where freshwater products serve as a critical reservoir for the emergence and transmission of antimicrobial resistance genes with high risks. Pickled aquatic products are also potential sources of food safety risk， which require strengthened surveillance.

Abstract:Objective To establish a method for determining reasonable control levels of perchlorate in raw materials for infant formula by applying a probabilistic model.Methods Based on the levels of perchlorate in the raw materials of infant formula and the constituent ratio of ingredients， a probabilistic model between raw materials and final products was established using Monte Carlo simulation and the key influencing raw materials were identified through sensitivity analysis. The content threshold of perchlorate in the key raw material， which is the reasonable control level， was found by using step-back method according to the limit of perchlorate in infant formula.Results At the initial levels of perchlorate contamination in raw milk， milk powder， lactose， whey protein powder and other ingredients collected in this study， the probability that the perchlorate level in the final product exceeded the limit value set by the European Union， which is 1.6% when a certain formula is used to manufacture infant formula. Sensitivity analysis showed that raw milk was the ingredient that has the greatest impact on the perchlorate content in the final product. Given that the perchlorate in other raw materials remains the current level， the perchlorate content in raw milk should be controlled below 43.6 μg/kg， to ensure a probability exceeding 99.9% that the perchlorate content in infant formula powder remains below the regulatory limit value. When taking this value as the risk control level for perchlorate in raw milk， the current ratio of raw milk samples exceeding this level was approximately 3.5%.Conclusion The method established in this study can effectively simulate the probability distributions of stable chemical contaminants when transferring from raw materials to the final product and identify the most influential ingredient. By applying this method， the reasonable control level of perchlorate in raw materials of infant formula can be proposed， providing a scientific basis for infant formula enterprises to prevent and control risks associated with raw materials.

Abstract:Objective To investigate the distribution patterns and population exposure risks of rare earth elements （REEs） in vegetables from typical rare earth mining areas across four provincial-level administrative divisions in China （Guangdong， Guangxi， Shandong， Sichuan）， and to provide scientific evidence for establishing regulatory policies on REEs in food.Methods A total of 963 vegetable samples were collected from mining and non-mining areas in these four provinces （autonomous region）， where China’s major rare earth deposits are located. Inductively coupled plasma mass spectrometry （ICP-MS） was employed to quantify 16 REEs， followed by systematic analysis and exposure risk assessment using a simple distribution assessment model.Results REE concentrations in vegetables from mining areas were significantly higher than those from non-mining areas （P<0.05）， with the most pronounced differences observed in cerium （Ce）， lanthanum （La）， and neodymium （Nd）. The average concentrations of 16 REEs in mining area vegetables， ranked in descending order， were Ce > La > Nd. Light rare earth elements （LREEs） predominated over heavy rare earth elements （HREEs）. Significant variations in REE levels were identified across vegetable categories： bulb and leafy vegetables exhibited universally higher concentrations， whereas cucurbitaceous （Cucurbitaceae） and Brassica vegetables （e.g.， cole crops） showed relatively lower levels. The average daily dietary exposure to REEs through vegetable consumption for residents in mining areas was 4.4 times higher than that for non-mining area residents， accounting for 4.12% of the acceptable daily intake （ADI）， indicating health risks remain within acceptable limits.Conclusion Elevated REE levels in vegetables from rare earth mining areas and significantly higher population exposure risks highlight the urgent need to evaluate the impacts of natural environmental factors and mining/smelting activities on REE exposure in these regions.

Abstract:Objective To assess the quality of the literature related to the carcinogenicity of perfluorooctane sulfonic acid （PFOS） using the weight of evidence method， and to evaluate its carcinogenic risk through the dose-response analysis.Methods A systematic search for relevant literature on human epidemiologic studies related to PFOS and cancer up to June 2024 was conducted. After evaluation and secondary screening， based on the guidelines for evaluating the relevance and reliability of toxicological data developed by the China National Center for Food Safety Risk Assessment， the dose-response for breast cancer risk analysis was performed using the cancer slope factor （CSF） method in conjunction with the results of meta-analyses of population-based epidemiological studies.Results From the 2 532 retrieved human epidemiological articles， 35 valid ones were screened， of which 22 were of high quality and 13 were of moderate quality in terms of the reliability. Thirty-two articles were graded as “A/B” or “B” in terms of the relevance. Meta-analysis showed that both low serum PFOS levels （<4.77 ng/mL； OR=1.46， 95% CI： 1.18-1.80） and moderate serum PFOS levels （>4.77 ng/mL and ≤15.67 ng/mL； OR=1.07， 95% CI： 1.04-1.10） were positively associated with the risk of breast cancer. The CSF results indicated that for every 1 ng/kg BW/d increment in external PFOS exposure， the attributable risk of breast cancer incidence increased by 1.64×10^-3.Conclusion Evidence from the weight-of-evidence evaluation integrated with meta-analysis confirmed a significant dose-response association between PFOS exposure and population-level breast cancer incidence， suggesting that PFOS exposure may be associated with an increased risk of breast cancer.

Abstract:Objective To investigate the prevalence and antimicrobial resistance of diarrheal Escherichia coli （DEC） isolated from surveillance cases of diarrhea from 2016 to 2023 in Tongzhou District， Beijing.Methods The antimicrobial susceptibility tests were carried out using microbroth dilution method. The whole genome was sequenced on illumina sequencing platform， and the antimicrobial resistance genes were identified through blasting with CARD database.Results From 2016 to 2023， the detection rate of DEC in Tongzhou District was 7.45% （226/3 033）. Among all DEC isolates， most of them were enterotoxigenic Escherichia coli （ETEC）， followed by enteropathogenic Escherichia coli （EPEC） and enteroagglutinative Escherichia coli （EAEC）. The multi-drug resistant rate was 41.59% （94/226）， from which strains resistant to three antimicrobials were dominant. The antimicrobial resistance rate of all isolates was higher against ampicillin， tetracycline， nalidixic acid and cotrimoxazole， and was relatively lower against polymyxin E， tigecycline and amikacin. The changes of antimicrobial resistance rates of ampicillin， ampicillin-sulbactam and ciprofloxacin in different years were statistically significant， and an increasing trend in antimicrobial resistance rates was observed. The multidrug-resistant isolates carried 64 antimicrobial resistance genes in 8 classes， including β-lactam （bla_TEM， bla_CTX， bla_AmpC， bla_EC）， Tetracycline （tetA）， quinolones （qnrS1） and folate pathway antagonists （sul1， sul2， drfA17）.Conclusion High multidrug resistant rate of DEC in Tongzhou District， and the harboring of multiple antimicrobial resistance genes in DEC， which have the potential to spread among different bacteria through horizontal gene transfer， were raising a public health concern. Therefore， antimicrobial resistance monitoring should be strengthened to provide better guidance for clinical antibiotic usage.

Abstract:This article focused on the applicability of supportive testing method standards of national food safety standard， GB 24154—2015， general guidance on sports nutrition food， in China. There are many types of sports nutrition food， and their substrates are complicated. In addition to the conventional nutrients such as vitamins and minerals， they may also contain characteristic nutrients like creatine， peptides， and amino acids. The accuracy and scientific characteristics of the corresponding testing methods need to be put forward to meet higher requirements. The product standard is currently under revision， and most of the nutritional component testing methods have been adapted. There are still some nutritional components with insufficient and missing testing methods. It is recommended that the supportive testing method standards be improved synchronously with the revision of the product standard to align with new product classifications and ingredient requirements. This research can help improve the standard， promote the standardization of the industry， and give an example for the subsequent revision of the standard.

Abstract:Objective This study aimed to analyze the epidemiological characteristics of Salmonella spp. in the whole chicken production chain in China from 2003 to 2023， in order to understand their prevalence， serotypes and antimicrobial resistance profiles.Methods Through searching the databases of CNKI， PubMed， and Web of science， 192 publications involving Salmonella associated with the chicken production chain in China and published from 2003 to 2023 were retrieved， and from them the data were grouped and statistically analyzed by SPSS， R and Excel. The data was divided into four time periods： T1 （2003—2007）， T2 （2008—2012）， T3 （2013—2017）， and T4 （2018—2023）. Contemporary reported data on Salmonella contamination， serotypes and antimicrobial resistance from the European Union and the United States were analyzed for comparison.Results Based on literature review， the prevalence of Salmonella in the whole chicken production chain in China from 2003 to 2023 was 17.6%， and the retail （33.7%） and slaughtering （21.3%） stages were higher than the hatching （14.9%） and breeding stages （12.7%）. The positive rate of Salmonella in the slaughtering and retail stages was significantly higher than that in the European Union and the United States （P<0.01）. The dominant serotypes of Salmonella in chicken production chain in China were S. Enteritidis （34.8%）， S. Pullorum （12.0%）， S. Indiana （9.2%）， S. Typhimurium and S. Typhimurium monophasic variant （5.2%）， S. Kentucky （3.7%）. There was a fluctuation in the serotype proportion of Salmonella from chickens at different time period. The S. Kentucky increased in the T2-T4 time period， while the S. Indiana and S. Enteritidis decreased. With S. Enteritidis， S. Typhimurium and S. Typhimurium monophasic variant being the dominant serotypes among China， the European Union and the United States， some serotypes had regional differences. Analysis of Salmonella resistance to 11 antimicrobial drugs showed that the overall resistance rate of Salmonella in China was above 90% during 2003—2023， and the resistance rate in the T4 time period was higher than that in the other three time periods. The multidrug resistance rate showed an increasing trend over time periods.S. Pullorum demonstrated the highest resistance rate （100.0%） to nalidixic acid， while S. Indiana showed the highest resistance to ampicillin （90.0%） and tetracycline （75.7%）. In China， the European Union， and the United States， resistance rates for both tetracycline and ampicillin ranked among the highest. However， the overall resistance level in China was higher than that in the European Union and the United States.Conclusion Literature data analysis showed that the contamination and drug resistance rate of Salmonella from the whole chicken production chain in China were relatively high， and it is necessary to strengthen the scientific guidance and supervision on chicken production in China.

Abstract:Livestock and poultry products are important reservoirs for antibiotic resistance genes （ARGs）， which have become a new type of environmental pollutant. The ARGs contained in these products， together with heavy metal pollution， pose a severe threat to the ecological environment. Livestock and poultry products （LPPs） carrying ARGs can transmit antibiotic resistance to humans through production and food chains， potentially leading to treatment-resistant infections and endangering public health. Studies have found a significant correlation between heavy metal concentrations and the abundance of ARGs in livestock and poultry products， with heavy metal contamination promoting the transmission and spread of ARGs. The combined pollution of antibiotics and heavy metals raises the overall level of bacterial resistance in both livestock products and their farming environments， directly harming the ecological environment and human health. This paper reviews the research progress on ARGs and heavy metal pollution in livestock and poultry products， explores the mechanisms of interaction between ARGs and heavy metals， and provides a strategic framework for future research directions in this field.