Rapid identification of Streptococcus bovis by using combination constitutive enzyme substrate hydrolyses

Several studies have documented the association of blood and rectal-culture positivity for Streptococcus bovis with gastrointestinal neoplasia, especially colonic carcinoma. Conventional methods using bile-esculin hydrolysis, salt tolerance, and sugar fermentations to differentiate S. bovis from other streptococci are laborious, slow, and relatively expensive. Commercially available systems are costly and require at least 24 to 48 h of incubation. A rapid identification procedure for S. bovis and related bacteria was developed. The method uses a reagent containing two hydrolyzable substrates, p-nitrophenyl-alpha-D-galactopyranoside and 4-methylumbilliferyl-beta-D-glucoside, in the presence of 2.5% sodium deoxycholate. This combination test, performed with a rapid assay for L-pyrrolidonyl-aminopeptidase, could distinguish S. bovis, Streptococcus equinus, Enterococcus spp., Streptococcus pneumoniae, and the viridans group streptococci in culture within 30 min. Twelve species of the genera Streptococcus and Enterococcus were tested. The rapid method correlated well with conventional techniques. The reagents are readily available, inexpensive, and easy to make and can be stored in the refrigerator for at least 6 months.