In vitro sensitivity of Mycobacterium marinum to minocycline and doxycycline

Using a Steers replicator technique the in vitro sensitivities of 32 clinical isolates of Mycobacterium marinum to doxycycline and minocycline were tested. Of 32 strains, sensitivity to doxycycline ranged from 3 strains (9%) with a drug concentration of 2 microgram/ml to 11 strains (34%) at a concentration of 6 microgram/ml. Sensitivity to minocycline ranged from 2 strains (6%) at the 2microgram/ml concentration to 23 strains (72%) at the 8 microgram/ml concentration. Our data suggest that a significant percentage of M. marinum strains are sensitive to therapeutically achievable levels of doxycycline and minocycline. These drugs may prove clinically useful in treating infections caused by sensitive strains of M. marinum.