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Updated: Jun 20, 2026

Deferred Growth Inhibition Assay to Quantify the Effect of Bacteria-derived Antimicrobials on Competition
Published on: September 3, 2016
INHIBITION OF BACTERIAL GROWTH BY DRUGS OF THE MORPHINE SERIES
Abstract:
The growth of Escherichia coli is reversibly inhibited by drugs of the morphine series. The order of inhibitory effectiveness for the drugs tested was levallorphan > levorphanol > dextrorphan > nalorphine > morphine. The synthetic analgesic, levorphanol, was studied in greater detail. Its effectiveness was found to be strongly dependent on the pH of the medium. Raising the pH of the medium provides a higher concentration of the neutral free base which is thought to diffuse across cell membranes more readily. However, considerations other than the rate of entry of drug into the cells must be of importance since an already established growth inhibition is promptly reversed upon lowering the pH of the medium. Two mutants of Escherichia coli with altered sensitivity to levorphanol were isolated.
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