INRA, UMR1253, F-35000 Rennes, France.
Appl Environ Microbiol. 2011 Feb;77(4):1493-500. doi: 10.1128/AEM.02233-10. Epub 2010 Dec 17.
In most ripened cheeses, bacteria are responsible for the ripening process. Immobilized in the cheese matrix, they grow as colonies. Therefore, their distribution as well as the distance between them are of major importance for ripening steps since metabolites diffuse within the cheese matrix. No data are available to date about the spatial distribution of bacterial colonies in cheese. This is the first study to model the distribution of bacterial colonies in a food-type matrix using nondestructive techniques. We compared (i) the mean theoretical three-dimensional (3D) distances between colonies calculated on the basis of inoculation levels and considering colony distribution to be random and (ii) experimental measurements using confocal microscopy photographs of fluorescent colonies of a Lactococcus lactis strain producing green fluorescent protein (GFP) inoculated, at different levels, into a model cheese made by ultrafiltration (UF). Enumerations showed that the final numbers of cells were identical whatever the inoculation level (10(4) to 10(7) CFU/g). Bacterial colonies were shown to be randomly distributed, fitting Poisson's model. The initial inoculation level strongly influenced the mean distances between colonies (from 25 μm to 250 μm) and also their mean diameters. The lower the inoculation level, the larger the colonies were and the further away from each other. Multiplying the inoculation level by 50 multiplied the interfacial area of exchange with the cheese matrix by 7 for the same cell biomass. We finally suggested that final cell numbers should be discussed together with inoculation levels to take into account the distribution and, consequently, the interfacial area of colonies, which can have a significant influence on the cheese-ripening process on a microscopic scale.
在大多数成熟奶酪中，细菌负责成熟过程。它们被固定在奶酪基质中，形成菌落生长。因此，它们的分布以及它们之间的距离对于成熟步骤非常重要，因为代谢物在奶酪基质中扩散。目前尚无关于奶酪中细菌菌落空间分布的数据。这是首次使用非破坏性技术对食品基质中细菌菌落分布进行建模的研究。我们比较了（i）基于接种水平计算的菌落理论三维（3D）平均距离，同时考虑到菌落分布是随机的，以及（ii）使用荧光标记的乳球菌（Lactococcus lactis）菌株产生的绿色荧光蛋白（GFP）的共聚焦显微镜照片进行的实验测量，该菌株在不同水平下接种到超滤（UF）制成的模型奶酪中。计数结果表明，无论接种水平如何（10(4)到 10(7) CFU/g），最终细胞数量都是相同的。结果表明，细菌菌落呈随机分布，符合泊松模型。初始接种水平强烈影响菌落之间的平均距离（从 25 μm 到 250 μm），也影响其平均直径。接种水平越低，菌落越大，彼此之间的距离越远。接种水平增加 50 倍，与奶酪基质的交换界面面积增加 7 倍，而细胞生物量相同。最后，我们建议将最终细胞数量与接种水平一起讨论，以考虑到分布，从而考虑到菌落的界面面积，这可能对微观尺度的奶酪成熟过程产生重大影响。
