Tetracycline resistance in Mycoplasma hominis

The composition of the cytoplasmic membrane of a clinical isolate of Mycoplasma hominis that was resistant to tetracycline (minimal inhibitory concentration, 30 micrograms/ml) was compared with that of a susceptible strain (minimal inhibitory concentration, less than 1 microgram/ml). Neither differences in passive permeability of the lipid portion of the membrane to the drug nor modulation of active transport by membrane lipids explained the resistance to tetracycline. Polyacrylamide gel electrophoresis revealed several differences between the membrane protein composition of the two strains. One 25,000-dalton protein was prominent in the membrane of the resistant strain but almost nonexistent in that of the sensitive strain. Therefore, the resistance may have been correlated with differences in protein composition. Preliminary evidence suggested that the resistance trait was plasmid-mediated.