Susceptibility of beta-hemolytic streptococci to 65 antibacterial agents.

Tests for susceptibility of 29 group A, 4 group C, and 2 group G strains of beta-hemolytic streptococci to 63 antibiotics and to trimethoprim and sulfamethoxazole, singly and combined in a ratio of 1:16, were carried out in vitro. All strains tested were moderately or highly susceptible to all the antibiotics used except those belonging to the aminoglycoside and polymyxin groups. A few were also resistant to the tetracyclines and to sulfamethoxazole alone. Comparisons with results obtained in previous years indicate that, except for the tetracyclines and sulfonamides, there has been no change in the susceptibility of beta-hemolytic streptococci to the most important and useful antibiotics, particularly penicillin.