Susceptibility of streptococci to newer tetracyclines and cephalosporins and to other antimicrobial agents.

Two hundred and thirty-nine strains of Streptococcus including 71 strains of Group A, 81 strains of Group B, 69 strains of enterococci, and 18 strains of S. pneumoniae were tested against 12 antimicrobial agents using an agar dilution method. Cefamandole was the most active cephalosporin tested. Doxycycline and minocycline were more active than tetracycline, although the tetracyclines were considerably less inhibitory than the cephalosporins. Regression line analysis of zones of inhibition versus minimal inhibitory concentration values for tetracycline and minocycline showed the tetracycline disc to be unacceptable for predicting the susceptibility of the Group A Streptococcus to minocycline. Minimal inhibitory concentrations for clindamycin, erythromycin, chloramphenicol, nitrofurantoin, and spectinomycin are also given.