SUMMARY: Resistance of 111 to tetracycline was due to an extrachromosomal genetic unit (plasmid) that could be eliminated by growth at 44°. The susceptible (eliminated) strain actively concentrated tetracycline from the nutrient medium by an energy-dependent transport system. The resistant culture accumulated the drug to a much lesser degree than the susceptible culture, both according to the 380 of the bacterial extract and to its radioactivity after incubation with tritiated tetracycline. Accumulation of tetracycline was low and independent of the external concentration until this reached a level corresponding approximately to the minimal inhibitory concentration.

Pre-incubation with tetracycline at low concentrations decreased ability to accumulate the drug. This pre-incubation effect was not prevented by nalidixic acid but was by actinomycin D.


Article metrics loading...

Loading full text...

Full text loading...

This is a required field
Please enter a valid email address
Approval was a Success
Invalid data
An Error Occurred
Approval was partially successful, following selected items could not be processed due to error