Species identification of members of the Streptococcus milleri group isolated from the vagina by ID 32 Strep system and differential phenotypic characteristics

Abstract

The importance of bacterial vaginosis as a risk factor in obstetric and gynecological infections has recently been recognized. The bacterial vaginosis group of organisms includes members of the Streptococcus milleri group, the identification of which has caused much confusion. We prospectively surveyed the rates of carriage of S. milleri group organisms in 397 high vaginal swabs received in our laboratory. For the identification of 99 clinical isolates and 23 control strains, we compared the results obtained by the rapid ID 32 Strep system (Analytab Products) and by a scheme utilizing six differential phenotypic characteristics (presence of beta-N-acetylglucosaminidase, alpha-glucosidase, beta-D-fucosidase, beta-galactosidase, beta-N-acetylgalactosaminidase, and beta-glucosidase) as described by Whiley et al. (R. A. Whiley, H. Fraser, J. M. Hardie, and D. Beighton, J. Clin. Microbiol. 28:1497-1501, 1990). We identified Streptococcus anginosus in 18% and Streptococcus constellatus in 0.05% of the specimens examined. Of the isolates of S. anginosus that reacted with grouping antisera, 20 of 25 belonged to Lancefield group F. The incubation conditions for bacterial cultures and for reaction mixtures affected the results of phenotypic characterization in the production of alpha-glucosidase, beta-galactosidase, and beta-glucosidase. However, by using bacterial cultures grown under hypercapnic conditions and incubating the reaction mixtures aerobically, consistent phenotypic characteristics were obtained, allowing identification similar to that obtained by the ID 32 Strep system. We therefore recommend the phenotypic scheme as an inexpensive, reliable, and convenient method for the initial identification of species of the S. milleri group.