Comparison of Three M17 Media for the Enumeration of Streptococcus thermophilus in Fermented Dairy Products.

Three M17 agar media for the enumeration of Streptococcus thermophilus in fermented dairy products, such as yogurt and other commercial fermented milk, were compared: CM785 Oxoid, 15108 Merck, and a M17 made in the laboratory. In all cases, the highest counts were taken on Oxoid medium. The difference between the averages of the counts on the Oxoid M17 and the laboratory-made M17 is significant, (P ≤ 0.05). However, the difference between the counts on the Oxoid and Merck media is not significant.