Effect of monovalent cations on assimilation of tetracycline antibiotics by bacteria.

The action of monovalent inorganic cations -Li+, Na+, K+, Rb+, Cs+, NH4+ - on assimilation of tetracycline antibiotics by Gram-positive (Staphylococcus aureus), and Gram-negative (Escherichia coli) bacteria sensitive and resistant to these antibiotics, was studied. It was found that K+ ions and, to a lesser degree, Rb+ and NH4+ ions, stimulate assimilation of tetracyclines by these microorganisms when incubated in Tris-buffer. The action of K+ ions is exhibited over a wide range of concentrations from 0.1 to 20 mM. In the case of Staph. aureus the action of K+ and Rb+ is exhibited after lag phase about 5 min in duration, but in the case of E. coli, the action of these ions is exhibited soon after their addition to the incubation medium. In all cases NH4+ ions act without a lag phase. The possible mechanisms of the effect of inorganic cations on assimilation of tetracyclines by bacteria are discussed.