Automated immunofluorescent speciation of oral bacteria using flow cytometry

Mixtures containing two bacterial species were analyzed using flow cytometric techniques. Light scattering characteristics of Streptococcus mutans and Actinomyces viscosus show unique profiles for pure cultures. However, the light scatter analysis of a mixture containing these two species demonstrates overlapping near the origin. Thus, light scatter analysis was not sufficient to speciate bacteria with different morphologies. Labeling of samples with species-specific immunofluorescent antibodies permitted speciation of mixtures. As the percentage of the bacterium to which the antibody is directed increased in a two-component mixture, fluorescent flow cytometric analysis showed a corresponding increase in the percentage of cells displaying fluorescent labeling. These methods could permit the rapid identification of bacteria from oral sites without culturing.