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Appl Environ Microbiol. 1966 May; 14(3): 386-390
Copyright © 1966 American Society for Microbiology. All Rights Reserved.

Identification of Fluorescent-Antibody Labeled Group A Streptococci by Fluorometry

Instrumentation Field Station, Heart Disease Control Program, Division of Chronic Diseases, Department of Health, Education, and Welfare, Washington, D.C.
George Washington University Hospital, Washington, D.C.
Division of Laboratories, Connecticut State Department of Health, Hartford, Connecticut

ABSTRACT

A quantitative system, amenable to automation, for determining the presence of group A streptococci in broth culture is described. After separation from the broth, the cells' protein coats are removed by digestion with 0.1% trypsin, and they are then stained with anti-A fluorescent antibody (FA). Excess FA is removed, and bound FA is put into solution by dissociation with demineralized distilled water. The amount of FA bound to the cells is quantitated by fluorometry of the solution. The level of nonspecific staining is measured by staining the cells with fluorescein-conjugated normal rabbit globulin absorbed with group A cells, dissociating, and quantifying, as above. The two quantities are subtracted to measure specific binding of FA to group A cells. A clinical trial showed 92% agreement with microscopists.