THE SEPARATION FROM YOGHURT CULTURES OF LAGTOBACILLI AND STREPTOCOCCI USING REINFORCED CLOSTRIDIAL AGAR AT pH 5·5 AND PLATE COUNT AGAR INCORPORATING MILK

Reinforced clostridial agar, best known for its use in the isolation of Clostridia species, has been shown to be selective for Lactobacillus bulgaricus found in yoghurt by suppressing the growth of Streptococcus thermophilus when the pH of the agar is 5·5. Str. thermophilus was isolated on plate count agar (PCA) incorporating 10 per cent milk by incubating at 37°C for a maximum of 24 h, since L. bulgaricus colony development was only sparse after this period of incubation.