Susceptibility of Staphylococci to Minocycline In Vitro: Identification of Group III Bacteriophage Types by Characteristic Inhibition of Growth.

Minocycline in concentrations of 1.0 mug per ml or less inhibited growth of 50 staphylococcal isolates which were tested by the broth dilution method. All strains were resistant to penicillin and tetracycline, and 34% were resistant to lincomycin. Minocycline discs identified two populations of minocycline-susceptible strains. The first group with small zones of inhibition surrounding the disc had multiple resistance and all were lysed by group III phage (84/85). The organisms with larger diameter of zones of inhibition were less frequently resistant to the antibiotics tested, and only 7.4% of these organisms were lysed by the 84/85 phage.