Susceptibility of Acinetobacter calcoaceticus var. anitratus (Herellea vaginicola) to minocycline.

The in vitro activity of minocycline against Acinetobacter calcoaceticus var. anitratus (Herellea vaginicola) was examined. All strains of A. anitratus were inhibited by minocycline at concentrations of 0.4 mug/ml or less. The strains studied were considerably more susceptible to minocycline than tetracycline. No difference between the susceptibility to minocycline and tetracycline was seen with Escherichia coli, Klebsiella pneumoniae, Enterobacter and Proteus sp. A regression line of the log minimal inhibitory concentration (MIC) values and the diameter of the zone of inhibition, determined by the Kirby-Bauer technique, showed good linear correlation for minocycline. Comparison of the disk diffusion results and MICs indicated that an inhibitory zone size of 19 mm produced by a 30-mug minocycline disk was equivalent to a MIC of 3.1 mug/ml, a serum concentration achieved by oral administration of the drug. When the zone of inhibition was greater than 19 mm, however, there was poor correlation with the MIC for Enterobacteriaceae.