1959 Volume 12 Issue 4 Pages 154-158
Experimental studies were made on the quality of tomato juice agar, plate count agar, and delta's fuchsin lactose agar for the detection and count of lactic bacteria in fermented milk and acidmilk drinks.The results obtained are summarized as follows.
1) Tomato juice agar is an excellent plate medium for the detection and count of lactic bacteria.
2) Plate count agar, as well as tomato juice agar, has a good qualility to favor the growth of lactic bacteria.It is difficult, however, to differentiate lactic bacteria from others by use of this medium. When B. C. P. is added to this medium at the rate of 0.006%, lactic bacteria change the color of the indicator used around a colony to yellow. Accordingly, the differentiation of lactic from non-lactic bacteria can be made comparatively with case.
3) Lactic streptococci grow selectively on Delta's fuchsin lactose agar and the growth of lactic bacilli and other bacteria is controlled on this medium.
4) From the results mentioned above, tomato juice agar and B. C. P.-added plate count agar are recommended for the direct plate count of lactic bacteria and Delta's fuchsin lactose agar is available for distinguishing bacilli from cocci.
5) With these media, t he detection and count of the estimated number of lactic bacteria were carried out in 10 samples of fermented milk and acid-milk drinks and the following results were obtained.
In fermented milk, the largest number of lactic bacteria was 72×109/cc and the smallest 63×108/cc, while in acid-milk drinks, the largest number was 24×1010/cc and the smallest 26×105/cc.
In fermented milk, 3 of 4 Yoghurt samples contained Lact.bulgaricus as starter, and the remaining one contained Lact. bulgaricus and Str. lactis. Only one sample of fermented milk contained Lact. acidophilus as starter. In acid-milk drinks, 2 of 5 samples contained. Lact. bulgaricus and the remaining 3, Lact. acidophilus as starter.
