Presumptive identification of group A, B, and D streptococci on agar plate media

Abstract

Several presumptive tests were evaluated for their effectiveness in differentiating streptococci [isolated from human skin, throat, wounds, blood and CSF]. When the tests were combined into a battery and the resulting reactions were interpreted as patterns, the overall presumptive identification rate was at least 97%. The hemolytic reaction, susceptibility to bacitracin and sulfamethoxazole plus trimethoprim (1.25 .mu.g plus 23.75 .mu.g), standard CAMP [Christie, Atkins, Munch-Peterson test] reactions on sheep blood Trypticase soy agar and bile-esculin and 6.5% of NaCl agar tolerance tests with incubation in candle extinction jars were used. Subsequently, 98.9% of group A, 95.3% of group B, 100% of .beta.-hemolytic non-group A, B or D, 92.3% of group D enterococcal, 100% of group D non-enterococcal and 92.8% of the viridans streptococci were presumptively identified. The hemolytic reactions, susceptibility of bacitracin and sulfamethoxazole-plus-trimethoprim disks, CAMP disk reactions on sheep blood Trypticase soy agar and bile-esculin and 6.5% NaCl agar tolerance tests with incubation in normal atmosphere were used. Subsequently, 98.1% of group A, 98.6% of group B, 99.2% of .beta.-hemolytic non-group A, B or D 97.5% of group D enterococcal, 97.6% of group D non-enterococcal and 92.4% of the viridans strains were presumptively identified.