Serological grouping ofstreptococci byslide agglutination

SUMMARY Streptococcal grouping seraforgroupsA,B,C,andG prepared forconventional testing byprecipitation weremadespecific byabsorption andusedtoidentify streptococci byslide agglutination withandwithout staphyloccocal coagglutination. Trypsinised suspensions of1055 strains, identified byprecipitation asbelonging togroupA,B,C,orG,weretested byslide agglutination. Ofthese, 998werecorrectly identified using astreptococcal suspension andantisera alone anda further 65were identified whena loopful ofprotein A-positive staphylococci was added. Suspensions of88strains notofgroupsA,B,C,orG gaveno reaction intheagglutination test withor without theaddition ofstaphylococci. Grouppolysaccharide extracted byconventional methods also caused agglutination ofstaphylococci on a slide whenspecific antiserum was added. Growthfromprimary or secondary cultures digested instreptomyces enzyme foronly15-30 minutes provided an excellent antigen fora quick andsimple methodofstreptococcal grouping using non-sensitised staphylococcal suspension andspecific antisera forcoagglutination. Theserological grouping ofstreptococci isnot performed asfrequently asitshould be,perhaps because thetechniques areslowandthereagents costly. Attempts havebeenmadetoovercome these drawbacks (Dajani, 1973; ElKholy etal., 1974). More recently, attention hascentred onanagglutination technique asa streptococcal grouping procedure (Christensen etal., 1973; Edwards andLarson, 1974; Hryniewicz etal., 1976; Tebbutt etal., 1976). Slide agglutination, asdescribed byRosendal (1956), is still usedsuccessfully inDenmark, butelsewhere the commercially available grouping antisera intended foruseinprecipitation arenotsufficiently specific forthemoresensitive agglutination test, andthe methodfailed togain widepopularity. Pharmacia Ltdproduce a coagglutination kit (Phadebact) forstreptococcal grouping. However, thereagents areexpensive andtheshelf-life comparatively short. Itemploysa suspension of Staphylococcus aureus rich inprotein A towhichthe groupantibody isnon-specifically absorbed. When mixedonaslide withasuspension ofastreptococcus ofthehomologous group, rapid coarse agglutination follows. Groupantigen isalso found inthesupernates