An Extracorporeal Model of Biofilm-Adherent Bacterial Microcolony Colonization for the Study of Peritonitis in Continuous Ambulatory Peritoneal Dialysis

Abstract

We have developed an extracorporeal system for investigating in vitro the biofilm-adherent bacterial microcolonies (BABM) that grow on Tenckhoff catheters (TC), to study peritonitis in patients undergoing continuous ambulatory peritoneal dialysis (CAPD). A modified Robbins’ device, attached to sampling plugs with TC discs and connected to the dialysate via a peristaltic pump, is run for 24 h; scrapings from pairs of TC discs are processed for assessment of viable BABM, one of each pair for culture by routine microbiology techniques and the other for examination by scanning and transmission electron microscopy (EM). No colonization was noted with fresh dialysis solutions and spent dialysates from patients without clinical peritonits; but, when bacterial suspensions were added to aliquots of the same dialysates, BABM were noted on both culture and EM. In a study of 4 patients on CAPD treatment, who had clinically evident peritonitis, routine cultures of spent dialysate were positive in only 2, but BABM were found in cultures and EM preparations of disc scrapings in all 4 cases. We conclude from these preliminary findings that this extracorporeal system is reliable, and well suited for studying the role of BABM in CAPD-associated peritonitis in vitro.

Significance of Biofilm-Adherent Bacterial Microcolonies on Tenckhoff Catheters of CAPD Patients

“…As our earlier studies [13,14] had evalu ated BB growth on TC that had been re moved, and thus did not establish that dis semination of BB in the peritoneal cavity may cause peritonitis, we developed an in vitro method to evaluate this with the TC remaining in place [21], In summary, we found minute amounts of BB (4-8%) in CAPD effluents from patients without peri tonitis but more than 60% BB growth in effluents from 4 patients who had peritoni- tis. Also we noted in control experiments that the growth of coagulase-negative S. epidermidis on TC disks in biofilm-adherent form, in this in vitro system, was dosedependent [22], These results indicate that BB colonization may act as a source of peri tonitis or as a reservoir of infection leading to peritonitis.…”

“…This is in keeping with the spectrum of bacteria responsible for peritonitis in CAPD patients [15,16]. Also, the production of biofilms by these bacterial populations in different human infections is well documented in the literature [1,9,11,12,[17][18][19][20], These studies [13,14] were made on TC that had been removed. Extensive BB colon ization developed over time on both the extra-and intraluminal surfaces of the TC in both control and study groups and, surpris ingly, the extent of BB growth on TC re moved from different groups of patients, with and without peritonitis, was similar.…”

“…In two parallel studies, published in 1986 and 1987 [13,14], we found bacterial bio films covering large areas of the subcuta neous and intraperitoneal surfaces of TC re moved from patients after varying periods of implantation, with and without peritoneal dialysis. These well-established biofilms were seen on direct morphological examina tion of TC that had been washed more than 20 times during processing for scanning elec tron microscopy and large numbers of bacte rial cells were seen by transmission electron microscopy.…”

“…Although all Hick man catheters recovered from leukemic pa tients in a Maryland study were colonized by sessile BB [9], only a few patients had expe rienced bacteremia. Similarly, we have found biofilm colonization of TC from three disparate groups of CAPD patients: (1) who had undergone dialysis and had not had peri tonitis; (2) who had been dialyzed and had had one or more episodes of peritonitis, and (3) who had not yet been dialyzed [13,14], These findings suggest that host defense factors are the most important determinants of whether the dissemination of planktonic bacterial cells from biofilm reservoir popula tions is a direct cause of peritonitis in CAPD patients. Prospective studies by Keane and Peterson [24], Keane et al [25] and Lamperi and Carozzi [26,27] showed that peritoneal dialysis itself constitutes a hazard, because it dilutes complement, immunoglobulin, lym phokines and phagocytic activity, weakening host defenses against bacterial proliferation in the peritoneal cavity.…”

Testing the susceptibility of bacteria in biofilms to antibacterial agents

“…This type of growth confers on the cells the ability to avoid attack by host defenses and an increased resistance to antimicrobial agents (11,12). Antibacterial agents are used for the control of biofilm-associated infections; however, the dosages of antibacterial agents used are, in many instances, below the concentrations required for the elimination of bacteria growing in glycocalyx-protected biofilms (4,6,12,16).…”