RAPID DETECTION OF GROUP A β-HEMOLYTIC STREPTOCOCCI BY DIRECT IMMUNOFLUORESCENCE

Group A β-hemolytic streptococci is the most important etiology of bacterial pharyngitis. Since rheumatic fever and glomerolonephritis which are both serious diseases of man, are the sequelae of streptococcal pharyngitis, so rapid laboratory diagnosis of the infection is an important for rapid treatment and prevention of post-streptococcal diseases. Conventional bacteriological methods take at least 48 hours to identify this bacteria. The aim of this project was to detect group A β-streptococci by direct immunofluorescence within 8-10 hours. For this purpose, group A β-hemolytic streptococcus strain ATCC 1447 was cultured into 300 ml of Todd-Hewitt broth and was incubated with shaking at 37º C with overnight shaking. Following centrifugation, the bacteria were collected and after treatment, whole bacteria were used as antigens for immunization of rabbits. After the titer of anti-streptococci in rabbit sera reached to a sufficient level, the immune sera were collected, its immunoglobulins were sedimented and conjugated with FITC. Serial dilution of conjugated immune sera were prepared and smears of various bacteria (S. aureus, Streptococuus pyogen, group B, C, and α-streptococci) were stained with conjugated serum and observed under UV microscope. The result showed that the reagent can detect Streptococcus pyogen reliably. Of the strains examined by this method, only Streptoccus pyogen showed 4+ in compare with S. aureus which showed 2+ positivity (brightness). The specificity and sensitivity of the method was determined 96.1% and 94.4% respectively.