Sir.—Subsequent to the article by Maruyama et al (Journal 1979; 133:1143-1145), which reported resistance of group A streptococci to erythromycin, our group performed resistance studies to penicillin, erythromycin, and cephalosporin on 200 group A streptococci cultures. We found all to be sensitive to each antibiotic.
We used the standard Kirby-Bauer disk sensitivity method, as follows: We first isolated group A β-streptococci from cultures of throat material by use of the bacitracin disk method. Tryptic soy broth was inoculated with a few colonies of β-streptococci and incubated to desired turbidity (about eight hours). The broth culture was then streaked in three planes onto a Mueller-Hinton plate supplemented with sheep blood. With flamed forceps, antibiotic disks of penicillin (10 units), erythromycin (15 μg), and cephalosporin (30 μg) were added. Plates were incubated overnight at 35 °C and zone diameters read the next day against known ranges for each antibiotic tested. Our