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Studies on antibiotic synergism against enterococci: II. Effect of various antibiotics on the uptake of 14C-labeled streptomycin by enterococci

Robert C. Moellering, Jr. and Arnold N. Weinberg

1Infectious Disease Unit and Department of Medicine, Massachusetts General Hospital and Harvard Medical School, Boston, Massachusetts 02114

Published December 1, 1971

The mechanism by which agents that inhibit bacterial cell wall synthesis produce a synergistic effect against enterococci when combined with aminoglycoside antibiotics has not been elucidated. Using 14C-labeled streptomycin, it could be shown that uptake of this aminoglycoside antibiotic was markedly enhanced in enterococci growing in the presence of penicillin or other agents which inhibit the synthesis of bacterial cell walls. There was no enhancement of streptomycin uptake when the cells were incubated with antibiotics which primarily affect the bacterial cell membrane or inhibit protein synthesis. Increased streptomycin uptake was produced by penicillin only in actively growing bacteria. These observations are consistent with the hypothesis that enterococci exhibit a natural barrier to the entry of streptomycin which can be overcome by agents which inhibit cell wall synthesis, thus producing a synergistic effect.

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