Fusidic acid resistance inRhodococcus erythropolisdue to an inducible extracellular inactivating enzyme

Fusidic acid is a steroid antibiotic inhibiting Gram-positive microorganisms. The mechanism of resistance previously characterised involves mutation alteration of the target moiety, protein synthesis elongation factor EFG. In the nocardioform bacterium Rhodococcus erythropolis, a novel resistance mechanism to this antibiotic was found, i.e., an inducible extracellular fusidic acid-in-activating enzyme. The presence of this enzyme increased roughly 30-fold the antibiotic concentration at which the organism could grow.