An analysis of Streptococcus pneumoniae identification using biochemical and serological procedures

Five methods for identification of Streptococcus pneumoniae were evaluated with stock strains representing all 83 capsular types and 130 fresh clinical isolates of alpha-hemolytic streptococci. The identification methods included bile solubility, optochin sensitivity, countercurrent-immunoelectrophoresis (CIEP), and coagglutination (CoA) using laboratory-prepared reagents (LPR) and the Phadebact Pneumococcus Test (Phadebact). The Quellung reaction was performed on the 83 capsular types of S. pneumoniae and on the clinical isolates that produced serological cross reactions with the three serological tests and those that were bile-soluble and optochin-sensitive. All 83 pneumococcal types were in complete agreement with each of the different test methods. Of the 130 alpha-hemolytic streptococci, 26 were identified as S. pneumoniae, and 104 isolates were identified as viridans streptococci using biochemical, physiologic, Quellung, or mouse virulence tests. All 104 viridans streptococci were bile-insoluble and optochin-resistant; however, 63 reacted with either one, both, or all three serological methods. Our data suggest that bile solubility and optochin tests are more reliable for pneumococcal identification than serological methods currently available.