Modifying effects of pH and temperature on (14C)erythromycin uptake into Staphylococcus aureus--relation to antimicrobial activity.

The uptake of (14C)erythromycin into Staphylococcus aureus was investigated by use of a rapid centrifugation method. Erythromycin uptake was saturable with time and with increasing erythromycin concentrations (apparent uptake constant Km = 6.0 x 10(-7) moles/l). Inhibitors of glycolysis, respiration and oxidative phosphorylation did not influence the uptake process but uptake was decreased by reducing temperature. Increases of erythromycin uptake, decreases of half life times of the uptake reaction and a log dose linked to enhancement of antimicrobial activity were seen with alkaline pH levels of the incubation medium. The experimental data conform well with the concept of non ionic diffusion. The high affinity of erythromycin to the intracellular ribosomal target site probably generates the driving force of uptake and the unionized antibiotic obviously represents the antimicrobially active molecular form.