The main objective of this study was to use bacteriocin producing Lactobacillus acidophilus strain LA-5 for the in situ lysis of Lactobacillus delbrueckii subsp. bulgaricus for reducing fermentation time, enhancing viability and survival of probiotic bacteria in fermented dairy foods, and for controlling post-acidification. To achieve these objectives it was necessary to study viability of probiotic bacteria in yoghurt and observe fermentation time and post-acidification.