Bacterial interference: effects of oral antibiotics on the normal throat flora and its ability to interfere with group A streptococci

Abstract

The effects of orally administered penicillin and tetracycline on the composition of the normal [human] throat flora [Neisseria spp., Micrococcus spp., diphtheroids, .alpha.-hemolytic and nonhemolytic streptococci] and its interference with the growth of group A streptococci were evaluated by throat culture and an agar overlay technique. Tetracycline caused only a slight, transient quantitative decrease in the composition of the flora and interference activity. Penicillin caused significant quantitative and qualitative decreases in the composition of the flora and interference activity. The diminution in interference activity persisted up to 3 wk after therapy. The differences observed between the antibiotic regimens correlated with differences in initial susceptibility of the flora to the antibiotic used and emergence of the resistance during therapy. Although effects of antibiotics on the composition of the flora are transient, effects on its ability to interfere with group A streptococci may persist long after therapy is discontinued. Penicillin therapy may enhance susceptibility of certain individuals to subsequent infection with group A streptococci.