Bacteriological Studies on Dairy Products

II. On Streptococci, Especially the Enterococcus Group Isolated

Abstract

The streptococci isolated from various dairy products in 1955 and 1957 were studied and identified, being especially taken into consideration the enterococcus group. At the same time, some selective media for isolation, identification, and count of entrococcus-group organisms were examined. The results obtained are summarized as follows.
1) Of 99 strains originated from 76 materials, 78 were identified as Streptococcus faecalis and 3 as Str. liquefaciens, but 18 remained unknown. Str. faecalis was identified in 55 of 57 strains originated from powdered milk and only 26 of 42 strains from butter.
2) The thermoresistance of the enterococcus group cultured in skim milk was tested by heating at 65°C for 30 minutes and at 75°C for 15 minutes. Of 81 strains, 70 survived in the former test and 15 in the latter test.
3) The streptococci which showed typical growth both in B.T.B.azide dextrose broth and on B. T. B. azide dextrose agar modified by NASU were presumed to be of the enterococcus group.
4) The presence of ethyl violet in the broth was not necessary for detection of the enterococcus group in dairy products.
5) Luxuriant growth of the enterococcus group in the above-described broth and in 0.1% methylene blue milk generally occurred at 37°C rather than 45°C.