Abstract: A small amount of bacterial spores with strong tolerance still exist in raw milk after sterilization and can multiply under certain conditions, causing a serious impact on product quality and consumer health. In this study, raw milk samples containing Bacillus were collected to isolate aerobic Bacillus and thermophilic aerobic Bacillus. The isolates obtained were identified based on their morphological, physiological, biochemical and molecular biological characteristics, and the heat resistance of the isolated thermophilic aerobic Bacillus was studied. Results showed that 10 strains of Bacillus were isolated from the milk samples, of which three were thermophilic aerobic Bacillus and seven were aerobic Bacillus. Among them, Bacillus coagulans and Bacillus clausii could tolerate heat treatment at 115 ℃ for 15 min. All Bacillus in raw milk could be killed by heat treatment at 121 ℃ for 20 min which decreased the number of spores by four orders of magnitude. The dominant Bacillus species in raw milk were Bacillus subtilis, Bacillus cereus, Bacillus pumilus, Bacillus licheniformis, Bacillus circulans, Bacillus gelatini, Bacillus amyloliquefaciens, Bacillus coagulans, and Bacillus clausii. Bacillus coagulans and Bacillus clausii had stronger heat resistance and could tolerate heat treatment at 115 ℃ for 15 min.

Key words: raw milk; Bacillus; identification; heat resistance

摘要： 生牛乳杀菌后残留少数芽孢具有极强耐受性，在一定条件下芽孢大量繁殖，使牛乳发生变质，严重影响产品品质和消费者健康。采集并选择含有芽孢杆菌的生牛乳样品，进行需氧芽孢杆菌和嗜热需氧芽孢杆菌的分离，通过形态学、生理生化和分子生物学方法对分离菌株进行鉴定，同时对分离到的嗜热需氧芽孢杆菌进行耐热性研究。结果表明：共分离出10?株芽孢杆菌，其中3?株为嗜热需氧芽孢杆菌，7?株为需氧芽孢杆菌，其中能耐受115?℃/15?min热处理的有凝结芽孢杆菌和克劳氏芽孢杆菌，121?℃/20?min热处理可以将生牛乳中芽孢杆菌全部杀灭，致死率达100%，芽孢数下降4?个数量级；生牛乳中芽孢杆菌的优势菌有枯草芽孢杆菌、蜡样芽孢杆菌、短小芽孢杆菌、地衣芽孢杆菌、环状芽孢杆菌、明胶芽孢杆菌、解淀粉芽孢杆菌、凝结芽孢杆菌和克劳氏芽孢杆菌；耐热性较强的有凝结芽孢杆菌和克劳氏芽孢杆菌，最高能耐受115?℃/15?min热处理。

关键词: 生牛乳；芽孢杆菌；鉴定；耐热性