Rapid, colorimetric test for the determination of hippurate hydrolysis by group B Streptococcus

A colorimetric test for the determination of hippurate hydrolysis was developed. Brain heart infusion broth made with 1% sodium hippurate served as the test medium. Hydrolysis was determined by the addition of two chemical developers, M (rhodamine B) and A (uranium acetate). A dark pink color indicated hydrolysis; no color change indicated no hydrolysis. The method was efficacious in either rapid or overnight incubation. One hundred twenty-five strains of group B, 44 strains of group A, 15 strains of group C, and 10 strains of group G Streptococcus were tested. By using the Lancefield method as the standard, there was 100% agreement with both the colorimetric and ferric chloride tests for hippurate hydrolysis, and 96% agreement with the CAMP test.