COLONIZATION OF URINARY CATHETERS BY ESCHERICHIA-COLI AND PROVIDENCIA-STUARTII IN A LABORATORY MODEL SYSTEM

A laboratory model system was developed to investigate the progressive colonization of urinary catheters by Escherichia coli and Providencia stuartii, prominent organisms in the polymicrobial bacteriuria of the long-term catheterized urinary tract. We hypothesized that colonizati on of the catheter and artificial urine by E. coli is influenced by th e presence of P. stuartii. E. coli or P. stuartii in pure culture both rapidly colonized the artificial urine and catheters, and both persis ted throughout all experiments. In systems containing both organisms, P. stuartii occurred in significantly higher numbers in the artificial urine and on the catheters than E. coli (p < 0.05). To obtain similar numbers of E. coli and P. stuartii in the artificial urine, citrate w as eliminated; however, P. stuartii still dominated on the catheter su rfaces. The presence of P. stuartii appeared to facilitate growth of E . coli in the artificial urine, yet reduce numbers of E. coli on the c atheter. In a separate experiment using different strains of E. coli a nd P. stuartii, the latter was dominant in the artificial urine and on the catheter surfaces. However, this strain of P. stuartii (which was urease positive) did not facilitate growth of E. coli. The interactio n between these strains may have been considerably affected by urea hy drolysis, which resulted in an increase in pH (6.5 to > 8.5) and consi derable precipitate formation in the model system. The paradox of P. s tuartii enhancing colonization by E. coli in the artificial urine, yet inhibiting its colonization on the catheter surface, illustrates the complexity of polymicrobial interactions in colonization of the cathet erized urinary tract.