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ObjectiveTo investigate the serotype distribution and antimicrobial resistance characteristics of Salmonella isolated from retail chicken in Beijing City.MethodsA total of 135 Salmonella strains were isolated from retail chicken meat collected from three large wholesale markets in Fengtai District in Beijing City from 2014 to 2015. The serotype of these Salmonella strains was identified using both a Luminex serotyping kit and a traditional serum agglutination method. Multilocus sequence typing was performed according to the recommended conditions of the Enterobase database. Antimicrobial susceptibility testing plates were used to determine the susceptibility of the isolates against 12 classes of drugs representing 25 antimicrobial agents. PCR was used to detect the prevalence of the 10 mobile colistin resistance genes （mcr） and three NDM-type carbapenemases genes （blaNDM）.ResultsAmong the 135 Salmonella strains， 6 serogroups were detected， with D1 and B being the main serogroups； 20 serotypes were detected， in which Enteritidis， Indiana， and Thompson were the dominant ones with percentages of 50.4%， 15.6%， and 8.1%， respectively； 21 ST types were obtained， and a good correspondence was observed between serotypes and ST types. 91.9% of all tested isolates showed resistance to the tested drugs and showed the highest resistance to nalidixic acid， ampicillin， ampicillin-sulbactam， tetracycline. Multi-drug resistant strains accounted for 71.1% of all strains and were resistant to as many as 18 kinds of antimicrobial compounds belonging to 10 categories. Among the 17 strains co-resistant to 8 or more classes of drugs， 16 were of the Indiana serotype. The proportion of strains with high multi-drug resistance was different in different packaging methods， different seasons， and different wholesale markets. All strains were negative for the mcr and blaNDM genes.ConclusionThe serotypes of Salmonella isolates from chicken meat in wholesale markets in Beijing City from 2014 to 2015 were complex， with the dominant serotype of Salmonella Enterititis， and the overall antimicrobial resistance level of all isolates was high. To assess the possible food safety risks， continuous monitoring for Salmonella Indiana with high levels of antimicrobial resistance must be carried out and their drug resistance and transmission mechanisms must be studied to help develop first-line and ultimate drugs for clinical treatment of Salmonella diseases.

The microbial control in broiler chicken slaughtering and processing is essential in ensuring food safety and human health. Scalding， washing， and cooling are crucial stages for controlling microbial contamination during broiler chicken processing， and a combined use of multiple measures can effectively reduce microbial load on broiler chicken carcasses. Among these antimicrobial agents， sodium hypochlorite， cetylpyridinium chloride， and acidified sodium chlorite are effective in reducing contamination by pathogens such as Salmonella， Escherichia coli， and Campylobacter on broiler chicken carcasses. However， the effectiveness of reducing microbes depends on the stages of microbial control and the amount and duration of antimicrobial agent application. This article provides an overview of the control measures for microbial contamination at various stages of broiler chicken slaughtering and processing. Additionally， this study systematically elucidates the microbial reduction effects of various antimicrobial agents in these process stages. This review aims to provide data references for preventing and controlling microbial contamination during broiler chicken slaughtering and processing in domestic industries， thereby promoting the healthy development of the broiler production industry and safeguarding consumer health.

The lithology and hardness of the coal seam roof are directly related to the stability and water permeability of the roadway and the safe production of the coal mine. It has become a common method to predict gas content based on AVO inversion, but the conventional AVO inversion formula is a simplified approximation of Zoeppritz equation in different degrees under certain conditions, which affects the inversion accuracy to some extent. On the basis of petrophysical analysis of the roof, the pre-stack inversion of quasi-linear Zoeppritz equation with the smallest overall angle error was employed to lithology and hardness prediction of coal seam roof in Yangquan Mining Area, Shanxi Province. The results show that the expression of quasi-linear Zoeppritz equation is simple, and through the AVO characteristic analysis of different Zoeppritz approximate formulas, found that the precision of quasi-linear Zoeppritz equation is the highest, second only to that of accurate Zoeppritz equation. The analysis of rock mechanics characteristics shows that Young’s modulus multiplied by density is the most sensitive to hardness, and pseudo-gamma P-wave velocity can effectively reflect roof lithology. The lithology and hardness characterization parameters obtained from inversion are combined with the parameter well data and geological data to comprehensively evaluate the roof stability, provide geological evidence for roadway excavation and reduce the coal mine production risk.

ObjectiveA dual real-time polymerase chain reaction (PCR) method for simultaneous detection of two virulence genes tdh and trh of Vibrio parahaemolyticus was established, and the virulence genes carried by 2 771 strains of foodborne Vibrio parahaemolyticus in China were comprehensively detected.MethodsAccording to the tdh and trh virulence genes of Vibrio parahaemolyticus, PCR primers and fluorescent probes were designed respectively, the real-time PCR reaction system and reaction procedure were optimized, and a dual real-time PCR detection method which can detect the two virulence genes at the same time was established. The virulence genes carried by 2 771 strains of foodborne Vibrio parahaemolyticus isolated in 2015 and 2016 were detected by the established method, and compared with the result of PCR method to evaluate the sensitivity, accuracy and specificity of the method.ResultsThe established dual fluorescence PCR method could detect both tdh and trh virulence genes at the same time, and its sensitivity was 1.5×10-4 ng/μL. The accuracy and specificity were 100%. In 2015, the carrying rates of tdh and trh genes in foodborne Vibrio parahaemolyticus in China were 0.26% (3/1 137) and 1.67%(19/1 137) respectively, and were 0.24%(4/1 634) and 0.43%(7/1 634) in 2016 respectively.ConclusionIn this study, a dual real-time PCR method for simultaneous detection of tdh and trh virulence genes of Vibrio parahaemolyticus was established, which could quickly and accurately screen the virulence genes of Vibrio parahaemolyticus. The carrying rate of tdh and trh virulence genes of Vibrio parahaemolyticus isolated from food in China was low. The dual real-time PCR method can be applied to the study of the pathogenicity of Vibrio parahaemolyticus in food, and provide scientific data for the risk assessment of dietary exposure to Vibrio parahaemolyticus in China.

ObjectiveWhole genome sequencing and analysis was conducted on a Burkholderia gladiolus pv. cocovenenans strain, isolated from raw corn flour sample which caused family agglutinative bongkrekic acid poisoning. The genetic characteristics of its virulence and pathogenicity were analyzed as well.MethodsGenomic DNA was extracted from DBJ isolate, the whole genome sequencing was carried out. Bioinformatics method were used to mine and analyze the data obtained from sequencing.ResultsTwo independent chromosomes (G1 and G2) and one plasmid (P) were found in DBJ isolate. The lengths of the chromosomes and plasmid were about 4 Mb and 300 kb respectively. The GC content of the two chromosomes was both around 68.0%, and that of the plasmid was slightly lower at 63.0%. The bon gene cluster was found on chromosome G2. The phylogenetic analysis showed that DBJ isolate and UCD-UG_CHAPALOTE stain which was isolated from corn sample in Canada were in the same clade. Among 255 strains, 31 carrying bon gene cluster and they had obvious genetic evolutionary tendency.ConclusionThe bon gene cluster was located on the chromosome of Burkholderia gladiolus pv. cocovenenans DBJ, and it was the main pathogenic gene causing food poisoning in human.

Objective: To investigate the presence of tellurite resistance (ter) gene cluster and its resistance in Escherichia coli 0157 strains collected by national foodborn disease surveillance system from 2005 to 2007., Methods: The ter gene cluster was tested by PCR. Tellurite resistance was evaluated by plate dilution method., Results: Of the investigated 89 E. coli strains,the presence of ter gene cluster was found in 51 strains. They were separately from 41 of 42 E. coli O157: H7 strains,all of 6 strains of O157 : NM (non-mobile flicH7 positive) and only 3 of 41 O157: NM (flicH7 negative)/O157: hund strains. The 51 strains with ter gene cluster were resistance to the high level of potassium tellurite. The MIC was from 64-512 microg/ml. In contrast, the MIC of most of 38 strains without ter gene cluster was from 2-16 microg/ml. Only one strain was 128 microg/ml. 28 of 29 stx-positive E. coli isolates contained the ter gene cluster and had the high levels of tellurite resistance., Conclusion: E. coli 0157 from food had the diversity levels of tellurite resistance. The presence of the ter gene cluster had significant associated with the high levels of tellurite resistance.

Objective: To carry out isolation and the viable plate count of probiotics from yoghourt. To investigate the antimicrobial susceptibility of strains to penicillin, gentamicin, ampicillin, vancomycin, clindamycin and erythromycin., Methods: Probiotics were recovered and counted from yoghourt by plate count method. The recovered isolates were characterized by Gram's stain, biochemical test, antimicrobial susceptibility test., Results: MRS medium and (36 +/- 1) degrees C were the optimum condition of culture. In total, 52 probiotic isolates were recovered from 31 yoghourt products, 12 (38.7%) products showed a lower probiotic quantity than 1 x 10(6) cfu/ml of the national stantard, and 19 (61.3%) products were higher than 1 x 10(6) cfu/ml. Gram's stain showed that 37 isolates were gram positive bacilli and 15 isolates were positive coccus. These 52 isolates were grouped into six species by biochemical method, including L. bulgaricus, S. thermophilus, L. acidophilus, L. casei, L. delbrueckii and L. fermentum. All 52 isolates were susceptible to penicillin and ampicillin, one isolate was resistant to both clindamycin and erythromycin, four isolates were resistant to vancomycin., Conclusion: Most of yoghourt products contained sufficient viable probiotics as required by the national standard. A small quantity of isolates were resistant to some antimicrobials and multi -drug resistant isolates were also found.

Objective: To develop a PCR method for identifying the 16S rRNA of Lactobacillus and Streptococcus thermophilus at the species level., Methods: Optimizing the method for DNA extraction and the conditions for PCR amplification. Joining the PCR amplification products from 16S rRNA to plasmid puc18-T and detecting the sequence., Results: All 50 isolates recovered from yoghourt products were characterized by 16S rRNA sequence analysis and 7 groups were identified as L. bulgaricus (24 strains), S. thermophilus (12 strains), L. acidophilus (7 strains), L. casei (3 strains), L. delbrueckii (2 strains), L. fermentum (1 strain) and S. lutetiensis (1 strain)., Conclusion: 16S rRNA PCR method developed in this research is a sensitive and reliable method for the identification of both Lactobacillus and Streptococcus thermophilus.

Objective: To establish the principles for determination and evaluation of the preservative properties demonstrates the effectiveness of a substance when used as a food preservative., Methods: Sorbic acids were chosen as the model food preservative and the Gram positive bacterium Staphylococcus aureus, Gram negative bacteria Escherichia coli and Salmonella enteritidis, yeast Candida albicans and the filamentous fungus Aspergillus niger, A. flavas, Geotrichum candidum, Penicillium islandicum and Peniciuium cyclopium were employed as the experimental microorganisms. The test involves adding fresh and active cultures standardized to a concentration between 10(2) and 10(5) cfu/ml directly to sorbic acid solution at different concentrations ranged from 0.25 to 2 g/L to simulate contamination. The mixture was held for two days and microorganism survivals were monitored at regular intervals of 3, 6, 24 and 48 h, respectively., Results: Sorbic acids were active against an extensive range of bacteria, yeasts and molds. The inhibition got stronger and stronger with either the extension of time against microorganisms or the increasing in concentration of sorbic acid. The antibacterial activity of sorbic acid were a little bit stronger than its antimycotic activity, with the lower minimum inhibitory concentration and the shorter inhibitory time in bacteria than those in fungi. In general, Gram negative bacteria were more sensitive to sorbic acid than Gram positive one., Conclusion: The experimental design could be science-based, sound and available in evaluation of the antimicrobial effectiveness of food preservatives.

Lactobacillus species have been used in the food processing industry widely. The current state of evidence suggests that probiotic effects and safety of Lactobacillus are strain specific. The identity based on both species and strain is important to link a strain to a specific health effect as well as to ensure the safety of food containing this microorganism. Phenotypic and genetic tests are used at present. Technologies in isolation and identification of Lactobacillus on genus, species and strain basis are reviewed.