The migration of Proteus mirabilis and other urinary tract pathogens over Foley catheters

OBJECTIVE: To examine the ability of organisms that infect the catheterized urinary tract to migrate over the surfaces of Foley catheters. MATERIALS AND METHODS: In a simple laboratory model, organisms were challenged to migrate across sections of hydrogel-coated latex, hydrogel/silver-coated latex, silicone-coated latex and all-silicone catheters. The sections (1 cm long) were placed as bridges in channels between blocks of agar and the test organisms inoculated onto the agar adjacent to one side of each bridge. The plates were incubated at 37 degrees C for 24 h and examined for growth of the test organisms on the agar on the other side of the bridges. A collection of swarming, swimming and nonmotile species were tested in the model. The relative mobilities of the test organisms were expressed as migration indices, calculated as the percentage of tests in which bacterial migration was observed over each type of catheter bridge. RESULTS: The swarmer cells of Proteus mirabilis and P. vulgaris migrated successfully (migration indices of 73-100) over all four types of catheter. The migration index of Serratia marcescens swarmers was reduced to 33 over the silver-coated catheters, but these cells crossed over the other catheter surfaces with ease (indices of 100). Pseudomonas aeruginosa was the most mobile of the swimming, non-swarming organisms with indices of 70-22, but this group was less capable of migration than the swarmers. Indices were 0-33 for nonmotile organisms. The mean migration indices for the nine species for each type of catheter were 57 (hydrogel-coated latex), 49 (silver/hydrogel-coated latex), 41 (silicone-coated latex) and 35 (all-silicone). The swarmer cells of P. mirabilis moved through populations of Escherichia coli, Klebsiella pneumoniae, Staphylococcus aureus and Enterococcus faecalis, and then migrated over sections of hydrogel-coated latex catheters with little or no reduction in migration index. They were also capable of transporting the nonmotile cells of K. pneumoniae and S. aureus over the catheters. The migration index of P. mirabilis swarmers was substantially reduced in the presence of Ps. aeruginosa and S. marcescens. CONCLUSIONS: Hydrogel coatings facilitate the migration of urinary tract pathogens over catheter surfaces. With the exception of S. marcescens, the incorporation of silver into the hydrogel did not inhibit migration. Swarmer cells were particularly effective at moving over catheters and P. mirabilis swarmers were also capable of transporting other species. This suggests that inhibitors of swarming could be useful in controlling catheter-associated infection and the complications resulting from the spread of bacterial biofilm over catheters.