Identification and genetic diversity of Bacillus cereus strains isolated from a pasteurized milk processing line in Algeria

Abstract

Bacillus cereus is a food pathogen of major concern to the dairy industry. Strains of B. cereus were isolated in 2006 and 2010 from a pasteurized milk processing line in a dairy plant in Algeria. Pasteurized milk is obtained from reconstituted and processed milk powder. This study was designed to discriminate between the isolated B. cereus strains and to predict their food poisoning potential. Strains were fingerprinted by M13-PCR, and identified at the phylogenetic group level by amplified panC gene sequence analysis. They were clustered into three distinct M13-PCR groups: one major group which included 17 strains and two minor groups which contained two and one strains, respectively. Strains originating from both the process equipment and milk powder were from the major group indicating that milk powder was the main source of initial contamination. Strains from the major and second group were affiliated to the mesophilic phylogenetic group III while the unique strain of the third group was classified into the mesophilic phylogenetic group IV. The data presented in this study showed a very low genetic diversity among B. cereus strains identified in milk powder and secondly by milk processing systems, as well as persistence in the dairy environment of specific B. cereus genotypes, across 4 years. M13-PCR typing and phylogenetic affiliation were useful for characterizing B. cereus dairy isolates, permitting their differentiation within the B. cereus group, and showing homogeneous contamination throughout the pasteurized milk processing line. The recurrent genotypes which belong to the potentially toxigenic group III B. cereus could threaten pasteurized milk safety.

摘要:

蜡状芽孢杆菌是乳品行业中比较受关注的一种食品级病原菌。在2006年和2010年从阿尔及利亚乳品厂巴氏杀菌乳加工生产线上分离出蜡状芽孢杆菌。该工厂巴氏杀菌乳以复原乳和奶粉为原料。本研究目的是分离鉴别蜡状芽孢杆菌并预测他们对食物的潜在毒性。分离的菌株通过M13引物PCR指纹法分析,菌株的系统发育组别水平通过panC 基因序列分析法来鉴定。这些菌株被分成三个不同的M13-PCR菌群: 一个是具有17 菌株的大菌群和两个分别仅含有2株和1株的小菌群。这些菌株既来自加工设备,也来自奶粉,其中奶粉是菌株的主要来源物,奶粉是主要的污染源。来自主要菌群的菌株和次级菌群中的1株菌株属于嗜温菌种属III,然而第三组菌群中仅有的1株菌株属于嗜温菌种属IV。本研究的数据表明从奶粉和奶加工体系中分离的蜡状芽孢杆菌有较低的遗传多样性,在四年生产过程中特殊的蜡状基因型菌株一直存在于乳品环境中。M13-PCR 分类技术和菌种隶属对蜡状芽孢杆菌的定性很有用,允许蜡状芽孢杆菌菌属内部存在差异,同时表明了在整个巴氏杀菌乳生产线上存在相似的污染。重复出现的基因型菌株属于潜在的产毒蜡状芽孢杆菌属III,能够严重威胁到巴氏杀菌乳的安全。