预制食品中蜡样芽孢杆菌的污染情况与分离菌株的毒力及多位点序列分型分析

Contamination Status of Bacillus cereus in Prefabricated Foods and the Toxigenic Profiles and Multi-locus Sequence Typing of Isolated Strains

摘要:

为探究市售预制食品中蜡样芽孢杆菌（Bacillus cereus, B. cereus）的污染情况，根据国标GB 4789.14-2014对样品进行蜡样芽孢杆菌的检测及分离菌株的生化鉴定，并采用聚合酶链式反应（Polymerase Chain Reaction, PCR）方法对分离菌株进行毒力及多位点序列分型（Multi-Locus Sequence Typing, MLST）分析。结果表明，佛山市某地区97份预制食品中蜡样芽孢杆菌检出率为36.08%，其中冷冻类食品的检出率最高（54.17%）。97.14%的阳性样品污染水平超过3 log CFU/g，40.00%的阳性样品污染水平超过5 log CFU/g，存在较为严重的食品安全风险。35株代表性分离菌株均携带特征基因（gyrB）和肠毒素基因（hblD、nhe、entFM、cytK），其中发现1株菌株携带呕吐毒素合成酶基因（cesA）。MLST结果显示，分离菌株可分为18个序列型（Sequence Type, ST）。其中，ST177和ST2056为优势ST型，ST-205为优势克隆复合体，7株菌株确认为新的ST型，大多来源于冷冻类预制食品。综上，冷冻类预制食品的蜡样芽孢杆菌检出率及污染水平均较高，分离菌株携带多种毒力基因，呈现ST型多样性，需加强对预制食品中蜡样芽孢杆菌的风险监测与防控。

Abstract:

To characterize the contamination status of Bacillus cereus in commercially available prefabricated foods, its presence and the biochemical identification of isolated strains were investigated according to China’s national food and safety standard (GB 4789.14-2014). The toxigenic profiles and multi-locus sequence typing (MLST) of isolated strains were detected via PCR. Results showed that B. cereus was widely present in 97 samples of prefabricated foods obtained from Foshan City, China, with an overall detection rate of 36.08%. The detection rate was highest in frozen food products (54.17%). Among the positive samples, 97.14% were detected with viable counts >3 log CFU/g, and those of 40.00% were >5 log CFU/g, indicating a high food safety risk. All 35 representative isolated strains carried the feature (gyrB) and enterotoxin genes (hblD, nhe, entFM, cytK), and the cereulide synthetase gene (cesA) was detected in one strain. The MLST results showed that the isolated strains could be classified into 18 sequence types (STs), with ST177 and ST2056 being predominant and ST-205 representing the main clonal complex. Seven strains were identified as new STs, most of which were isolated from frozen prefabricated foods. In conclusion, the distribution and contamination levels of B. cereus in frozen prefabricated foods are relatively high. The isolated strains carried multiple virulence genes and exhibited ST type diversity, highlighting the need for monitoring and preventing B. cereus contamination in prefabricated foods.