Bacterial aggregation in relation to peritoneal dialysis.

The ability of gram-positive cocci to aggregate and form biofilms at the exit site and on catheter surfaces in continuous ambulatory peritoneal dialysis (CAPD) has been associated with peritonitis. In the present study, 16 (80%) of 20 dialysate effluents from patients with staphylococcal peritonitis were found to contain aggregates of Staphylococcus epidermidis or S. aureus. Using an in vitro assay system, 20 (83%) of 24 pathogenic bacterial strains were found to aggregate in fresh dialysis solutions within 4 to 24 h at 37 degrees C. Further studies with one strain, S. epidermidis 1938, showed increased aggregation when the bacteria were incubated in dialysate effluents compared to fresh dialysis solutions. Viability experiments showed that aggregated bacteria were less sensitive to the killing effects of fresh dialysis solutions and that dialysate effluents could support bacterial growth. The results suggest that attention be paid to aggregation as a potential mechanism used by bacteria in causation of peritonitis.