Many bacterial infections are associated with biofilm formation. In the urinary tract bacterial biofilms develop on both living surfaces and artificial implants, producing chronic and often intractable infections. Escherichia coli is the most common organism associated with urinary tract infections. In contrast to uropathogenic E coli (UPEC), which cause symptomatic urinary tract infection, asymptomatic bacteriuria (ABU) strains are associated with essentially symptom-free infections. Here the biofilm-forming capacity on abiotic surfaces of selected E coli ABU strains and UPEC strains in human urine was investigated. It was found that there is a strong bias for biofilm formation by the ABU strains. Not only were the ABU strains significantly better biofilm formers than UPEC strains, they were also able to out-compete UPEC strains as well as uropathogenic strains of Klebsiella spp. during biofilm formation. The results support the notion of bacterial prophylaxis employing selected ABU strains to eliminate UPEC strains and other pathogens in patients prone to recalcitrant infections.