Rapid identification of Streptococcus pyogenes by flow cytometry

Flow cytometry combined with immunofluorescence of Streptococcus pyogenes was used to assay bacteria suspended in buffer solution and in saliva derived from throat swabs of healthy volunteers. The method allowed the enumeration of as few as 5 × 10³ and 5 × 10⁴ CFU per milliliter of buffer and saliva respectively. Controls including Streptococcus salivarius instead of Streptococcus pyogenes or buffer instead of specific antibodies confirmed the specificity of the detection of Streptococcus pyogenes in the samples. The results suggest that flow cytometry may serve as a basis for an automated reliable method for the diagnosis of streptococcal infections.