Evaluation of a rapid system for species identification of alpha-hemolytic streptococci

A new 4-h commercial system (API 20S; Analytab Products, Plainview, N.Y.) for the identification of streptococci was compared with the conventional biochemical profile method in the species identification of alpha-hemolytic streptococci. A total of 194 clinical isolates (including 74 isolated from blood cultures, 64 isolated from wound cultures, and 56 isolated from respiratory cultures) and 20 reference strains were tested. Only 4 of the 20 reference strains were correctly identified to species level by the API 20S system. Six were identified to group level (viridans), four were incorrectly identified, and six did not conform to the identification key. Of the 194 clinical isolates tested, 79 (39%) were correctly identified to species level, 34 (17.5%) were identified to group level, 34 (17.5%) were incorrectly identified, and 50 (25.8%) did not conform to the identification key. Of the 12 different species of alpha-hemolytic streptococci isolated from clinical specimens, the API 20S system consistently identified Streptococcus faecalis and Streptococcus faecium, but consistently misidentified the other 10 species, especially Streptococcus mitis. Our results indicate that for identification to species level, the API 20S system is of little value for alpha-hemolytic streptococci other than enterococci.