
Full text loading...
Diagnostic Methods for Group A Streptococcal Infections, Page 1 of 2
< Previous page Next page > /docserver/preview/fulltext/10.1128/9781555815905/9781555813642_Chap50-1.gif /docserver/preview/fulltext/10.1128/9781555815905/9781555813642_Chap50-2.gifAbstract:
The M protein is a major virulence factor of group A streptococci. Antigenic differences within the hypervariable region at the N terminus constitute the basis for the Lancefield serological classification for group A streptococci. Identification of M types is accomplished using a precipitation reaction between M-protein antigen and type-specific antiserum. The antisera against the M-protein antigens are produced with whole-cell streptococcal (killed) vaccines used to immunize rabbits. M-protein antigen is extracted from streptococci using Lancefield's hot hydrochloric acid method. Rapid streptococcal antigen tests have overcome the inherent overnight delay associated with the culture method for identification of group A streptococci and have allowed clinicians to make management decisions based on laboratory data shortly after examining the patient. Nephelometry has been introduced as a simple, rapid procedure for quantitative measurement of anti-streptolysin O (ASO) titers. The principle of nephelometry is based on the ability to measure the rate of increase in light intensity scattered from particles suspended in solution as a result of complexes formed during an antigen-antibody reaction. The streptococcal antihyaluronidase determination is an enzyme neutralization test in which the antigen used is streptococcal hyaluronidase elaborated by the bacteria. It should be emphasized that the most common clinically used streptococcal antibody tests (ASO and anti-DNase B) provide evidence only for a preceding group A streptococcal infection.