The application of flow cytometry to the characterisation of a probiotic strain Lactobacillus reuteri DPC16 and the evaluation of sugar preservatives for its lyophilization

In this study, we applied flow cytometric (FCM) analyses to characterize the resistance of a probiotic strain Lactobacillus reuteri DPC16 (DPC16) against diverse stresses. Two fluorescent probes, propidium iodide (PI) and carboxylfluorescein diacetate (cFDA), were combined to the FCM method to reveal multiple cellular statuses of DPC16. The FCM results confirmed that the DPC16 strain had probiotic potential in respect of acid tolerance and bile acid resistance, whereby more than 60% of DPC16 bacteria remained intact after 1 h exposure to pH 2.0, and over half of DPC16 bacteria were unaffected by the presence of bile salts at a concentration of 0.2 g/100 mL for 1 h even without nutrient supply. In addition, the comparison among a number of lyo-preservatives for the DPC16 strain confirmed that lactose was able to maintain over 60% viable DPC16 bacteria after the lyophilization and subsequent storage period, outperforming all the other selected sugars. To conclude, the superior stress resistance of the novel DPC16 strain was confirmed by the FCM analyses in this study. The FCM technique also proved to be readily incorporated into probiotics research, and capable of providing insightful information. (C) 2011 Elsevier Ltd. All rights reserved.