Comparison of four methods for identifying Streptococcus pneumoniae

Four methods (bile solubility, optochin, latex agglutination, and DNA probe ) were compared for identification of clinical isolates of Streptococcus pn eumoniae. Of 209 isolates tested, 151 (Group I) were selected based on typi cal colony morphology of S. pneumoniae, while 58 (Group II) were selected o n the basis of alpha-hemolysis alone. Using the DNA probe as a reference me thod, 141 isolates from Group I and 10 from Group II were identified as S. pneumoniae. The optochin disk test and the latex agglutination test both ex hibited a 100% sensitivity and specificity for Group I isolates; bile solub ility identified all but 1 isolate in this group. For Group II isolates, th e sensitivity and specificity of optochin testing was 100%, 80 and 94% for latex and 80 and 100% for bile. The results of this study indicate that all methods tested give reliable results for isolates with typical colony morp hology of S. pneumoniae. Bile solubility and latex may not be as reliable w hen testing ol-hemolytic colonies without colony morphology typical S. pneu moniae. (C) 2000 Elsevier Science Inc. All rights reserved.