To optimize the quantitative detection method for Salmonella enterica and analyze the quantitative contamination level of Salmonella enterica in raw pork samples from farmer's markets in Chengdu. Based on qualitative detection standard method of Salmonella enterica in China (GB 4789.4-2016) and the quantitative detection method of FSIS in the United States (MLG 4.08 and MLG appendix 2.05 MPN), the selective enrichment broth, screening plate, identification method and quantitative dilution ratio in quantitative detection of Salmonella enterica were optimized using 70 samples of raw pork. The optimized method compared by student's t-test was used to detect 40 samples of raw pork collected from farmer's markets in Chengdu from June to October 2020. For isolation of Salmonella from raw pork samples, the coincidence degree of TTB enrichment solution was significantly higher than that of RV enrichment solution (0.93±0.32 vs 0.35±0.62,t=8.324,P=0.001) and the consistency of suspicious colonies screened by XLT4 plate was significantly higher than that of Salmonella chromogenic medium (0.77±0.09 vs 1.00±0.00,t=2.971,P =0.017). The MPN method used 4 successive gradient dilutions, namely 12 tube method, could obtain more accurate quantitative value for Salmonella enterica. The combined use of selective enrichment broth TTB, XLT4 plate, Real-time PCR and MALDI-TOF mass spectrometry could get better results for screening and identifying Salmonella enterica. The detection rate for Salmonella enterica isolated from raw pork in farmer's markets was 92.5% (37/40). The most of the Salmonella positive samples (83.8%, 31/37) were detected with a contamination level ranged from 0.1 to 55 MPN/g. The optimized quantitative detection method for Salmonella enterica in raw pork in this study can effectively screen the target bacteria and obtain more accurate quantitative value.
为了优化猪肉中沙门菌定量检测方法，并对成都市部分农贸市场零售的猪肉样品中沙门菌污染浓度进行定量研究。本研究于2020年基于我国沙门菌定性检测方法（GB4789.4-2016）和美国农业部食品安全检验局（Food Safety and Inspection Service，FSIS）定量检测方法（MLG 4.08和MLG Appendix 2.05 MPN），使用成都地区市售70份肉猪样品对沙门菌定量检测中选择性增菌液、筛选平板、鉴定方式以及定量稀释比例进行优化，通过t检验分析获得适用的优化方法，使用优化方法对2020年6—10月成都市部分农贸市场采集的40份零售猪肉样品进行沙门菌定量检测。结果显示，对于生鲜猪肉样本，TTB增菌液筛选沙门菌符合度显著高于RV增菌液（0.93±0.32 vs 0.35±0.62，t=8.324，P =0.001），XLT4平板筛选到的可疑菌落符合度显著高于沙门显色培养基（0.77±0.09 vs 1.00±0.00，t=2.971，P =0.017）。使用4个连续梯度稀释的12管MPN法，可获得准确的沙门菌污染浓度数值。经选择性增菌液TTB增菌后划线于XLT4平板，并使用荧光PCR联合MALDI-TOF微生物质谱鉴定，可实现猪肉样品中沙门菌高效分离鉴定。部分农贸市场零售生鲜猪肉中沙门菌的检出率为92.5%（37/40），大部分阳性样品（83.8%，31/37）沙门菌的污染水平在0.1~55 MPN/g范围。本研究优化的沙门菌定量检测方法，可有效对猪肉中沙门菌污染进行定量分析。.