Factors affecting the growth of enterococci in highly alkaline media.

The ability to grow in a medium at pH 9.6 was one of the tolerance tests suggested by Sherman and Stark (1934) for the identification of Streptococcus faecalis. Subsequent investigations have indicated that the ability to grow at this high pH is a general characteristic of the enterococcus group with the exception of some strains of Streptococcus durans (Smith and Sherman, 1938; Shattock and Hirsch, 1947; Shattock, 1955). Shattock and Hirsch (1947) pointed out some of the experimental difficulties in determining this characteristic and devised a liquid medium buffered with glycine that standardized the conditions of the test and gave more reproducible results. However, this laboratory has experienced some difficulty in obtaining consistent results with the method of Shattock and Hirsch. Skadhauge (1950) used a broth medium adjusted to pH 9.6 with sodium carbonate, apparently with good results. The present study has clarified some of the factors that may lead to erratic results with these tests.