Weber Mareike, Geißert Janina, Kruse Myriam, Lipski André
Rheinische Friedrich-Wilhelms-Universität Bonn, Institut für Ernährungs- und Lebensmittelwissenschaften, Abteilung Lebensmittelmikrobiologie und -hygiene, Meckenheimer Allee 168, 53115 Bonn, Germany.
Universität Tübingen, Institut für Medizinische Mikrobiologie und Hygiene, Elfriede-Aulhorn Str. 6, 72076 Tübingen, Germany.
J Dairy Sci. 2014 Nov;97(11):6761-76. doi: 10.3168/jds.2014-8340. Epub 2014 Sep 18.
Microbial diversity of 3 raw milk samples after 72 h of storage at 4 °C in a bulk tank was analyzed by culture-dependent and -independent methods. The culture-dependent approach was based on the isolation of bacteria on complex and selective media, chemotaxonomic differentiation of isolates, and subsequent identification by 16S rRNA gene sequencing. The culture-independent approach included the treatment of raw milk with the dye propidium monoazide before direct DNA extraction by mechanic and enzymatic cell lysis approaches, and cloning and sequencing of the 16S rRNA genes. The selective detection of viable bacteria improved the comparability between bacterial compositions of raw milk based on culture-dependent and -independent methods, which was the major objective of this study. Several bacterial species of the phyla Actinobacteria, Bacteroidetes, Firmicutes, and Proteobacteria were detected by the culture-dependent method, whereas mainly bacteria of the phylum Proteobacteria as well as low proportions of the phyla Bacteroidetes and Actinobacteria were detected by the culture-independent method. This led to the conclusion that the phylum Firmicutes was strongly discriminated by the culture-independent approach. Generally, species richness detected by the culture-dependent method was higher than that detected by the culture-independent method for all samples. However, few taxa could be detected solely by the direct DNA-based method. In conclusion, the combination of culture-dependent and -independent methods led to the detection of the highest bacterial diversity for the raw milk samples analyzed. It was shown that DNA extraction from raw milk as the essential step in culture-independent methods causes the discrimination of taxa by incomplete cell lysis. Treatment of raw milk with the viability dye propidium monoazide was optimized for the application in raw milk without former removal of milk ingredients and proved to be a suitable tool to ensure comparability of bacterial diversity depicted by both methods.
采用依赖培养和不依赖培养的方法,分析了3份原料乳样品在4℃的奶罐中储存72小时后的微生物多样性。依赖培养的方法基于在复杂和选择性培养基上分离细菌、对分离株进行化学分类学鉴别以及随后通过16S rRNA基因测序进行鉴定。不依赖培养的方法包括在通过机械和酶促细胞裂解方法直接提取DNA之前,用单叠氮碘化丙啶染料处理原料乳,以及对16S rRNA基因进行克隆和测序。对活菌的选择性检测提高了基于依赖培养和不依赖培养方法的原料乳细菌组成之间的可比性,这是本研究的主要目标。通过依赖培养的方法检测到了放线菌门、拟杆菌门、厚壁菌门和变形菌门的几种细菌,而通过不依赖培养的方法主要检测到了变形菌门的细菌以及少量拟杆菌门和放线菌门的细菌。由此得出结论,厚壁菌门在不依赖培养的方法中受到强烈区分。一般来说,所有样品通过依赖培养的方法检测到的物种丰富度高于通过不依赖培养的方法检测到的物种丰富度。然而,只有少数分类群可以仅通过基于直接DNA的方法检测到。总之,依赖培养和不依赖培养方法的结合导致在所分析的原料乳样品中检测到最高的细菌多样性。结果表明,在不依赖培养的方法中,作为关键步骤的从原料乳中提取DNA会因细胞裂解不完全而导致对分类群的区分。用活菌染料单叠氮碘化丙啶处理原料乳,在不预先去除乳成分就应用于原料乳方面进行了优化,并且被证明是确保两种方法所描述的细菌多样性具有可比性的合适工具。