Aims We hypothesized that pretreating urinary catheters with benign Escherichia coli HU2117 plus an antipseudomonal bacteriophage (FE2005-A) would prevent Pseudomonas aeruginosa biofilm formation on catheters a pivotal event in the pathogenesis of catheter-associated urinary tract infection (CAUTI). Methods and Results Silicone catheter segments were exposed to one of four pretreatments (sterile media; E. coli alone; phage alone; E. coli plus phage), inoculated with P. aeruginosa and then incubated up to 72 h in human urine before rinsing and sonicating to recover adherent bacteria. Pseudomonas aeruginosa adherence to catheters was almost 4 log10 units lower when pretreated with E. coli plus phage compared to no pretreatment (P < 0.001) in 24-h experiments and more than 3 log10 units lower in 72-h experiments (P < 0.05). Neither E. coli nor phage alone generated significant decreases. Conclusions The combination of phages with a pre-established biofilm of E. coli HU2117 was synergistic in preventing catheter colonization by P. aeruginosa. Significance and Impact of the Study We describe a synergistic protection against colonization of urinary catheters by a common uropathogen. Escherichia coli-coated catheters are in clinical trials; adding phage may offer additional benefit.