Cost-effective method of serotyping Streptococcus pneumoniae using staphylococcal co-agglutination.
Typing of Streptococcus pneumoniae to determine the serotype prevalence has paved the way for polyvalent vaccines to prevent invasive pneumococcal infection. Variation of serotype prevalence in different geographical areas necessitates typing of strains from these areas for effective vaccine protection. High cost of antisera very often is a hindering factor in undertaking this exercise. We have tried to evaluate typing by co-agglutination to reduce cost. Clinical isolates of S.pneumoniae from Pondicherry and surrounding Tamil Nadu were serotyped using antisera coated Staphylococcus aureus Cowan I strain and compared with standard quellung reaction. There was hundred percent correlation. By this method we could determine the serotypes causing invasive infections in this area. A commercially available Pneumotest kit was used as source of type specific antisera. Serotype 1 was found to be the major isolate (20.1%) by both the tests. Twenty-four isolates (13%) belonged to the nonvaccine types. Rest of the isolates was made up by serotypes 6, 5, 19, 23 and 12. Co-agglutination method was found to be a simple rapid and economical technique. Ten milliliters of the reagent could be made, using 0.1 ml of standard antisera. Shelf life was found to be six months at 40C.
Department of Microbiology, JIPMER, Pondicherry - 605 006, India.
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Rajalakshmi
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Kanungo