title: Application of propidium monoazide quantitative real-time PCR to quantify the viability of Lactobacillus delbrueckii ssp. bulgaricus.
abstract: In this study, a combination of propidium monoazide (PMA) and quantitative real-time PCR (qPCR) was used to develop a method to determine the viability of cells of Lactobacillus delbrueckii ssp. bulgaricus ND02 (L. bulgaricus) that may have entered into a viable but nonculturable state. This can happen due to its susceptibility to cold shock during lyophilization and storage. Propidium monoazide concentration, PMA incubation time, and light exposure time were optimized to fully exploit the PMA-qPCR approach to accurately assess the total number of living L. bulgaricus ND02. Although PMA has little influence on living cells, when concentrations of PMA were higher than 30μg/mL the number of PCR-positive living bacteria decreased from 106to 105cfu/mL in comparison with qPCR enumeration. Mixtures of living and dead cells were used as method verification samples for enumeration by PMA-qPCR, demonstrating that this method was feasible and effective for distinguishing living cells of L. bulgaricus when mixed with a known number of dead cells. We suggest that several conditions need to be studied further before PMA-qPCR methods can be accurately used to distinguish living from dead cells for enumeration under more realistic sampling situations. However, this research provides a rapid way to enumerate living cells of L. bulgaricus and could be used to optimize selection of cryoprotectants in the lyophilization process and develop technologies for high cell density cultivation and optimal freeze-drying processes.
authors: College of Food Engineering and Nutritional Science, Shaanxi Normal University, Xi' an, Shaanxi, P. R. China, 710119.
authors: Yuyu
authors: Y
authors: Shao
authors: Key Laboratory of Dairy Biotechnology and Engineering, Ministry of Education, Inner Mongolia Agricultural University, Hohhot, Inner Mongolia, P. R. China, 010018.
authors: Zhaoxia
authors: Z
authors: Wang
authors: Key Laboratory of Dairy Biotechnology and Engineering, Ministry of Education, Inner Mongolia Agricultural University, Hohhot, Inner Mongolia, P. R. China, 010018.
authors: Qiuhua
authors: Q
authors: Bao
authors: Key Laboratory of Dairy Biotechnology and Engineering, Ministry of Education, Inner Mongolia Agricultural University, Hohhot, Inner Mongolia, P. R. China, 010018. Electronic address: hepingdd@vip.sina.com.
authors: Heping
authors: H
authors: Zhang
mesh_terms: D000818:Animals; D001386:Azides; D001419:Bacteria; D005612:Freeze Drying; D048668:Lactobacillus delbrueckii; D050296:Microbial Viability; D011419:Propidium; D060888:Real-Time Polymerase Chain Reaction
chemical_list: D001386:Azides; D011419:Propidium
keywords: Lactobacillus delbrueckii ssp. bulgaricus ND02; live/dead cells; propidium monoazide; quantitative real-time PCR