Faculty of Natural and Agricultural Sciences, Department of Consumer and Food Sciences, University of Pretoria, Private bag X20, Hatfield 0028, Pretoria, South Africa.
Faculty of Natural and Agricultural Sciences, Department of Consumer and Food Sciences, University of Pretoria, Private bag X20, Hatfield 0028, Pretoria, South Africa.
J Dairy Sci. 2020 Jun;103(6):4991-5002. doi: 10.3168/jds.2019-17919. Epub 2020 Apr 16.
This study aims to characterize Bacillus subtilis complex group from raw, pasteurized, and packaged extended shelf-life (ESL) milk samples, to determine their biofilm potential and source-track the microbial contaminants to control their presence during processing. Isolates were characterized using multi-locus sequence typing (MLST) with 7 housekeeping genes. The primers used were designed from the coding regions with the highest number of polymorphic sites. The heat resistance profile indicated that all 12 isolates are psychrotolerant as well as thermophilic, with temperature ranges of 6°C to 55°C (B43, B44, B52, B54, B55, B56, B57), 6°C to 60°C (B46, B47, B48), and 15°C to 60°C (B49, B50). A general linear model 2-way repeated-measure ANOVA of the biofilm-forming potential of the isolates shows a statistically significant difference across the time of incubation (6, 12, 18, and 24 h). All isolates except 2 formed moderate to strong biofilms, with B44 having the most robust biofilm formation (3.14 ± 0.60). Scanning electron and confocal microscopy images reveal the strain specificity of the biofilm structure. The MLST analysis identified all isolates as belonging to either B. subtilis or Bacillus velezensis. All the isolates were novel sequence types (ST) when compared with the PubMLST database (https://pubmlst.org/) but showed relatedness to isolates in the raw milk that was processed. The closest ST are 96 for B. velezensis and 128 for B. subtilis, mostly isolated from soil. This study presents the significance of biofilms of thermophilic B. subtilis and B. velezensis and their possible perpetuation in the dairy processing plant. The information provided is a call for an innovative food contact surface or any other intervention that can minimize or prevent microbial adhesion in the processing plant, to prevent negative effects in ESL milk.
本研究旨在对生奶、巴氏杀菌奶和包装延长货架期（ESL）奶样品中的枯草芽孢杆菌复合群进行特征分析，以确定其生物膜形成能力，并追踪微生物污染物的来源，从而在加工过程中控制其存在。使用 7 个看家基因的多位点序列分型（MLST）对分离株进行特征分析。使用的引物是从具有最多多态性位点的编码区域设计的。耐热性分析表明，所有 12 个分离株均为嗜冷菌和嗜热菌，温度范围为 6°C 至 55°C（B43、B44、B52、B54、B55、B56、B57）、6°C 至 60°C（B46、B47、B48）和 15°C 至 60°C（B49、B50）。分离株生物膜形成能力的一般线性模型 2 向重复测量方差分析显示，在孵育时间（6、12、18 和 24 h）上存在统计学差异。除 2 株外，所有分离株均形成中度至强生物膜，其中 B44 的生物膜形成能力最强（3.14 ± 0.60）。扫描电子显微镜和共聚焦显微镜图像显示了生物膜结构的菌株特异性。MLST 分析将所有分离株鉴定为枯草芽孢杆菌或解淀粉芽孢杆菌。与 PubMLST 数据库（https://pubmlst.org/）相比，所有分离株均为新的序列类型（ST），但与加工生奶中的分离株具有相关性。最接近的 ST 是解淀粉芽孢杆菌的 96 和枯草芽孢杆菌的 128，主要从土壤中分离得到。本研究介绍了嗜热枯草芽孢杆菌和解淀粉芽孢杆菌生物膜的重要性及其在乳制品加工厂中的可能持续存在。提供的信息呼吁使用创新的食品接触面或任何其他干预措施，以尽量减少或防止加工厂中微生物的粘附，从而防止 ESL 奶产生负面影响。
