Effects of selective media and atmosphere of incubation on the isolation of group A streptococci

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Abstract
The effects of selective media and atmosphere of incubation on the isolation of group A .beta.-hemolytic streptococci were evaluated. Sheep blood agar medium with gentamicin (2.5 or 5.0 .mu.g/ml) was inferior to antibiotic-free sheep blood agar medium. This resulted from the partial restriction of group A streptococcal growth on gentamicin medium. Recovery of .beta.-hemolytic streptococci from specimens in air, CO2 or anaerobic incubation was evaluated. The isolation of group A streptococci was equivalent in the 3 incubation atmospheres; non-group A .beta.-hemolytic streptococci were isolated significantly more often from specimens incubated in an anaerobic or CO2 atmosphere than from those incubated in air. Sheep blood agar medium, stabbed with a wire loop and incubated in air, is recommended for the isolation of group A streptococci from [human] throat swabs [for prevention of sequelae of streptococcal pharyngitis].