The entry of meropenem into human macrophages and its immunomodulating activity.

The uptake of meropenem by human macrophages and its consequences upon subsequent phagocytosis and killing of intracellular staphylococci has been studied. The cellular to extracellular concentration ratios (C/E) of meropenem were always high (range 3-12) at extracellular concentrations ranging from 0.125 to 1 mg/L. The uptake was not energy-dependent, being similar when viable and formalin-killed cells were used and was influenced neither by environmental temperature nor by the addition of a metabolic inhibitor. Meropenem at half the MIC caused a significant enhancement of phagocytosis and a reduction in the survival of intracellular Staphylococcus aureus. Pre-exposure of either staphylococci or macrophages to sub-MIC concentrations of meropenem led to an increase in uptake of bacteria and intracellular bactericidal activity by macrophages.