Abstract
The in vitro antibacterial activity of minocyclin (7-dimethylamino-6-deoxy-6-demethyltetracycline), a new antibiotic, was compared with that of tetracycline (TC), demethylchlortetracycline (DMCT) and deoxytetracycline (DOTC).
Minocycline showed antibacterial activity against Gram-positive bacterial species, such as Staph. aureus, Strept. hemolyticus, Strept. mills, Strept. salivarius, Lact. fermenti, at the concentration of 0.2mcg/ml and proved to be the most active among 4 tetracycline derivatives. Against Gram-negative ones including E. coli and Salm. typhosa, the activity of minocycline was about equal to that of the other TC derivatives. Against Nocardia dentocariosus, it was equal to that of DOTC and superior to that of the other analogues. While, against Corynebacterium isolated from oral cavity and Pseudomonas aeruginosa, it was proved only in high concentration.
The histogram on the sensitivity of 86 strains of Strept. viridans to TC derivatives showed the peak of minimum inhibitory conc entration(MIC) at the concentration of 0.39 mcg/ml in TC and under 0.2 mcg/ml in DMCT, DOTC and minocycline. However, minoczcline inhibited most frequently under 0.2 mcg/ml. In TC, DMCT and DOTC, the peak of MIC for resistant strains was revealed at the concentration of 6.25 to 12.5mcg/ml, but was not observed in minocycline. Against 17 TC resistant strains, the mean activity of DMCT and DOTC was 4 to 8 times higher than that of TC and that of minocycline was 4 to 16 times.
From the results obtained, in which the broad antibacterial spectrum and the bacteriocidal activity to Gram-positive strains was proved and also the activity to the many strains of Strept. viridans, especially, to the TC resistant strains was proved, minocycline seems to be effective, to the oralinfections from the point of antibacterial activity.
