title: Identification of group A streptococci by direct fluorometry.
abstract: A simple direct fluorometric method for rapid identification of group A streptococci is described. The method permits the detection of the organism in mixed cultures without the aid of a microscope and is amenable to automated processing of specimens. Experience with the indirect fluorometric method revealed that nontrypsinized cells from a 10-fold dilution of overnight broth cultures could be stained with uniform brilliance with fluorescent antibody (1:15 dilution) and that fluorescent antibody dissociated from such cells at 55 C for 20 min gave serologically specific fluorometric values. With this information, it was possible to develop a simpler fluorometric test which gave results comparable to those obtained by conventional cultural-precipitin grouping techniques. In the direct test described, cultures from throat swabs were incubated overnight, and cells from a 10-fold dilution were stained with specific fluorescent antibody (1:50 dilution) and then rinsed. The stained specimens were transferred to a continuous-filter paper strip (Whatman 3 MM) and read serially in a Turner 110 fluorometer with Corning 5840 and Wratten 2A filters in place. The reagents used required careful standardization and testing to assure that fluorometric readings above a specified value would be indicative of the presence of group A streptococci.
mesh_terms: D001331:Automation; D001431:Bacteriological Techniques; D005455:Fluorescent Antibody Technique; D005470:Fluorometry; D006801:Humans; D008722:Methods; D010614:Pharynx / Q000382:microbiology; D013210:Staphylococcus / Q000302:isolation & purification; D013291:Streptococcus / Q000302:isolation & purification; D013297:Streptococcus pyogenes / Q000302:isolation & purification*