Rapid Antibody Capture Assay for Detection Of Group-A Streptococci Using Monoclonal Antibody and Colloidal Gold-Monospecific Polyvalent Antibody Conjugate

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Abstract
A rapid one step, sensitive and specific antibody capture assay for detection of group-A streptococci from the throat swabs of children is described. Monoclonal antibody either MA-106 or MA-107 specific for group-A streptococci polysaccharide (APS) was used as the capture antibody on nitrocellulose paper and rabbit monospecific polyvalent antibody conjugated with colloidal gold to detect the presence of antigen. The lower detection limit of this assay is 15.6ng APS/ml. The assay is specific for APS and failed to recognize polysaccharides obtained from group-B, -C, -G streptococci as well as Staphylococcus aureus. Antigen extracted from throat swabs of children who were positive for β-hemolytic plaques (other than group-A streptococci) as seen on blood agar culture gave negative readings, thereby confirming the specificity of the assay for APS.