title: Rapid quantification of live/dead lactic acid bacteria in probiotic products using high-sensitivity flow cytometry.
abstract: A laboratory-built high-sensitivity flow cytometer (HSFCM) was employed for the rapid and accurate detection of lactic acid bacteria (LAB) and their viability in probiotic products. LAB were stained with both the cell membrane-permeable SYTO 9 green-fluorescent nucleic acid stain and the red-fluorescent nucleic acid stain, propidium iodide, which penetrates only bacteria with compromised membranes. The side scatter and dual-color fluorescence signals of single bacteria were detected simultaneously by the HSFCM. Ultra-high temperature processing milk and skim milk spiked with Lactobacillus casei were used as the model systems for the optimization of sample pretreatment and staining. The viable LAB counts measured by the HSFCM were in good agreement with those of the plate count method, and the measured ratios between the live and dead LAB matched well with the theoretical ratios. The established method was successfully applied to the rapid quantification of live/dead LAB in yogurts and fermented milk beverages of different brands. Moreover, the concentration and viability status of LAB in ambient yogurt, a relatively new yet popular milk product in China, are also reported.
authors.affiliation: The MOE Key Laboratory of Spectrochemical Analysis & Instrumentation, The Key Laboratory for Chemical Biology of Fujian Province, Department of Chemical Biology, College of Chemistry and Chemical Engineering, Xiamen University, Xiamen, Fujian 361005, People's Republic of China.
authors.forename: Shengbin
authors.initials: S
authors.lastname: He
authors.forename: Xinyi
authors.initials: X
authors.lastname: Hong
authors.forename: Tianxun
authors.initials: T
authors.lastname: Huang
authors.forename: Wenqiang
authors.initials: W
authors.lastname: Zhang
authors.forename: Yingxing
authors.initials: Y
authors.lastname: Zhou
authors.forename: Lina
authors.initials: L
authors.lastname: Wu
authors.forename: Xiaomei
authors.initials: X
authors.lastname: Yan
mesh_terms: D000818:Animals; D058491:Bacterial Load; D005434:Flow Cytometry / Q000379:methods; D005516:Food Microbiology; D007780:Lacticaseibacillus casei / Q000302:isolation & purification*; D008892:Milk / Q000382:microbiology*; D019936:Probiotics / Q000032:analysis*; D015014:Yogurt / Q000382:microbiology*