College of Food Engineering and Nutritional Science, Shaanxi Normal University, Xi'an, Shaanxi, China, 710119.
Key Laboratory of Dairy Biotechnology and Engineering, Ministry of Education, Inner Mongolia Agricultural University, Hohhot, Inner Mongolia, China, 010018.
J Dairy Sci. 2017 Nov;100(11):8776-8782. doi: 10.3168/jds.2017-12892. Epub 2017 Aug 31.
Differential enumeration of subpopulations in concentrated frozen and lyophilized cultures of Lactobacillus delbrueckii ssp. bulgaricus ND02 derived from 2 propagation procedures was determined. The subpopulations consisted of 3 categories (physiological states): viable cells capable of forming colonies on agar plates (VC+), viable cells incapable of forming colonies on agar plates (VC-), widely referred to as viable but nonculturable (VBNC) cells, and nonviable or dead cells (NVC). Counts of VC+ were recorded using a conventional plate count procedure. A fluorescent vital staining procedure that discriminates between viable (VC+ and VC-) and NVC cells was used to determine the number of viable and nonviable cells. Both propagation procedures had 2 variables: in procedure (P)1, the propagation medium was rich in yeast extract (4.0%) and the pH was maintained at 5.7; in P2, the medium was devoid of yeast extract and the pH was maintained at 5.1. The results showed that post-propagation operations-concentration of cells by centrifugation and subsequent freezing or lyophilization of cell concentrate-induced different degrees of transience from VC+ to VC- states in cells derived from P1 and P2. Compared with cells derived from P2, cells from P1 were more labile to stress associated with centrifugation, freezing, and lyophilization, as revealed by differential counting.
采用 2 种增殖程序浓缩冷冻和冻干的嗜热链球菌亚种保加利亚 ND02 培养物中的亚群进行了差异计数。亚群由 3 种类型（生理状态）组成：能够在琼脂平板上形成菌落的活细胞（VC+）、不能在琼脂平板上形成菌落的活细胞（VC-），通常称为活但不可培养（VBNC）细胞和非活或死细胞（NVC）。使用常规平板计数程序记录 VC+的计数。荧光活菌染色程序可区分活（VC+和 VC-）和 NVC 细胞，用于确定活细胞和非活细胞的数量。这两种繁殖程序都有 2 个变量：在程序（P）1 中，繁殖培养基富含酵母提取物（4.0%），pH 值保持在 5.7；在 P2 中，培养基不含酵母提取物，pH 值保持在 5.1。结果表明，继繁殖操作之后——通过离心浓缩细胞，随后冷冻或冻干细胞浓缩物——导致源自 P1 和 P2 的细胞从 VC+状态向 VC-状态发生不同程度的短暂转变。与源自 P2 的细胞相比，源自 P1 的细胞在与离心、冷冻和冻干相关的应激下更容易发生变化，这一点通过差异计数得到了揭示。
