Identification of β-haemolytic streptococci (BHS) in the diagnostic laboratory has depended traditionally on the use of presumptive tests in the first instance (Wilkinson, 1979). Definitive group identification rests on extraction of group-specific carbohydrate antigens and their reaction with specific antisera in capillary tubes or agar gel; counterimmunoelectrophoresis may also be used (Hill , 1975). Other methods of identification include slide agglutination tests (Christensen , 1973) and fluorescence staining (Moody, Ellis and Updyke, 1958).

The present study was undertaken to determine whether an enzyme-linked immunosorbent assay (ELISA) could be adapted to provide a reliable system for grouping BHS. Although this type of assay has been employed for detection of protein antigens and antibodies (Engvall and Perlmann, 1972; Russell, Facklam and Edwards, 1976), many workers have been unable to apply it to polysaccharide antigens, which have an overall negative charge that interferes with adsorption to polystyrene surfaces (Dr B. M. Gray, Dept of Pediatrics and Microbiology, University of Alabama in Birmingham, USA). In this paper we report that this difficulty can be overcome by adsorbing whole cells to polystyrene plates. Results of a trial of the ELISA procedure compared with a double-diffusion method in agar gel are presented.


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