Effect of bacterial products including endotoxin on neutrophil function in infected urine

Experiments were performed to determine the effects of products of bacterial growth (including endotoxin) on phagocytosis and intracellular killing by polymorphonuclear leucocytes (PMNL) in urine. Bacteriologically filtered supernates of two strains of Escherichia coli grown in urine were added in varying amounts to mixtures of PMNL and E. coli, also in urine. Phagocytosis of the two strains was reduced from > 90% in controls to 66% and 48%, respectively, in the presence of undiluted culture filtrate (containing endotoxin 2-2.5 micrograms/ml). Intracellular killing was also decreased and was abolished by dilutions corresponding to endotoxin concentrations of 0.6 and 0.75 micrograms/ml. When PMNL exposed to these inhibitory dilutions were resuspended in fresh urine, their phagocytic ability was fully restored and 13-24% of their killing activity was regained. A minimum concentration of commercially purified E. coli endotoxin of 200 micrograms/ml was required to abolished PMNL killing, with phagocytosis uninhibited. The results strongly suggest that bacterial growth metabolites, not endotoxin, are responsible for the depression of phagocytosis and intracellular killing in infected urine. A moderate dilution of the bacterial products in urine permits good PMNL function. Extrapolating this to the clinical situation, diluting the urine by water loading (as recommended for patients with urinary infections) should ensure efficient activity of PMNL under in-vivo conditions providing urinary pH and osmolality are not adversely affected.