Simultaneous detection and enumeration of viable lactic acid bacteria and bifidobacteria in fermented milk by using propidium monoazide and real-time PCR

Abstract This study describes a procedure that allows specific detection and enumeration of viable bacteria in four species of lactic acid bacteria ( Streptococcus thermophilus , Lactobacillus delbrueckii subsp. bulgaricus , Lactobacillus casei subsp. casei and Lactobacillus acidophilus ) and of Bifidobacterium lactis , mixed in fermented milk products. The procedure is based on the combined use of propidium monoazide (PMA), able to distinguish between viable and irreversibly damaged cells, with species-specific quantitative real-time PCR (RTi-PCR). Loss of viability of the species in a fermented milk through storage at 4 °C was similarly ( P