Comparison of media and techniques for detection of group A streptococci in throat swab specimens

Detection of group A streptococci in primary throat cultures was compared by using aerobic and anerobic incubation with selective nonselective media. Sheep blood agar plates incubated anaerobically detected 98% of the group A streptococci, whereas aerobically incubated blood agar plates which had been stabbed at the time of inoculation detected only 63%. Blood agar plates containing sulfamethoxazole and trimethoprim (23.75 and 1.25 mirograms per ml, respectively) detected only 70% of group A streptocci when incubated aerobically and 84% when incubated anaerobically.