Rapid immunochemical identification of enterococci with use of a centrifugal analyzer after a brief antigen-extraction step.

The precipitin reaction between antigens from enterococci and group-specific antisera was monitored turbidimetrically with a centrifugal analyzer. Linear standard curves (absorbance vs antigen concentration) were developed for studying optimal conditions for enzymic extraction of the antigen by use of an enzyme-containing filtrate from Streptomyces albus. This extraction was optimized by adding to the filtrate 1 mg of lysozyme per milliliter and incubating the bacteria for 40 min at 52 degrees C. The assay was adjusted so that detection of enterococci was indicated by positive absorbance changes near 0.1 A. When the concentration of bacteria from which the antigen was extracted was within a standardized range, non-enterococci produced no positive absorbance changes. Reproducibility of standard antigen and antisera solutions was excellent during three months. The procedure provides an objective, well-controlled means for identifying clinically important enterococci from pure cultures in about 1 h. In contrast, current methods involving biochemical media require as long as 48 h.