BACTERICIDAL ACTIVITY OF HUMAN PERITONEAL-MACROPHAGES FROM PATIENTS UNDERGOING PERITONEAL-DIALYSIS

Peritoneal macrophages (PM) play an essential role in the pathogenesis of bacterial peritonitis, the main complication of peritoneal dialysis (PD). We determined the antibacterial activity of PM from 31 PD patients using gram-positive (Staphylococcus aureus, Staphylococcus epidermidis) and gram-negative (Escherichia coli, Pseudomonas aeruginosa) test organisms. In an 8-hour test assay, PM revealed the highest antibacterial activity against E. coli [median bactericidal index (B(i)) = 5.46 representing 0.74 log growth inhibition compared to controls] and the lowest against P. aeruginosa (B(i) = 1.63, 0.21 log growth inhibition, p < 0.05). The antibacterial activity against S. aureus (B(i) = 1.99, 0.3 log growth inhibition) and S. epidermidis (B(i) = 2.0, 0.31 log growth inhibition) was within this range. When compared to peripheral blood polymorphonuclear leukocytes, PM reached only 4% (S. aureus) and 8.1% (E. coli) of their antibacterial activity (p < 0.05). Using E. coli as a test organism, PM isolated after a 4-hour dialysis period revealed the highest antibacterial activity when compared to PM isolated after longer dialysis periods (p < 0.05). Increasing the duration of PD to 6 and 8 h subsequently decreased the antibacterial activity of PM, suggesting that unphysiologic concentrations of toxic metabolites in the peritoneal effluent might have a harmful influence on PM functions.