Downloaded from www.microbiologyresearch.org by IP: 54.198.203.27 On: Wed, 30 Nov 2016 15:09:57 Biofilm exclusion of uropathogenic bacteria by selected asymptomatic bacteriuria Escherichia coli strains Lionel Ferrie ` res, Viktoria Hancock and Per Klemm Correspondence Per Klemm pkl@biocentrum.dtu.dk Microbial Adhesion Group, Center for Biomedical Microbiology, BioCentrum-DTU, Technical University of Denmark, Lyngby, Denmark Received 29 November 2006 Revised 24 January 2007 Accepted 7 February 2007 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. INTRODUCTION Urinary tract infection (UTI) is a serious health problem affecting millions of people each year. It is estimated that there are about 150 million cases in the world per year (Stamm & Norrby, 2001). The recurrence rate is high and often the infections tend to become chronic with many episodes. UTI usually starts as a bladder infection but often evolves to encompass the kidneys and ultimately can result in renal failure or dissemination to the blood. UTI is the most common infection in patients with a chronic indwelling bladder catheter; bacteriuria is essentially unavoidable in this patient group (Foxman, 2002). UTI is classified into disease categories by the site of infection: cystitis (the bladder), pyelonephritis (the kidney) and bacteriuria (the urine). The colonization of urine in the absence of clinical symptoms is called asymptomatic bacteriuria (ABU). ABU occurs in up to 6 % of healthy individuals and 20 % of elderly individuals. As the name implies, ABU strains generally do not cause symptoms; most patients with ABU do not need treatment and in many cases the colonizing organism actually helps to prevent infection by other more virulent bacteria (Darouiche et al., 2001). Escherichia coli is responsible for more than 80 % of all UTIs and causes both ABU and symptomatic UTI (Ronald, 2003). Generally, such infec- tions are caused by a single bacterial clone and are in effect mono-cultures. Based on the symptoms they produce, UTI E. coli can be divided into ABU E. coli and uropathogenic E. coli (UPEC) strains. Many bacteria live as sessile communities adhered to surfaces, rather than as planktonic isolated cells. These compact microbial consortia, referred to as biofilms, are commonly associated with many economic and health problems (Costerton et al., 1999). In medicine, biofilm- associated infections have a major impact on permanent and temporary artificial implants placed in the human body, often with devastating consequences. Moreover, biofilms associated with implants often serve as a source for recurrent infections. Many persistent and chronic bacterial infections are now believed to be linked to the formation of biofilms (Costerton et al., 1995, 1999). In the urinary tract, bacterial biofilms can develop on many living surfaces and virtually all artificial implants, producing chronic and often intractable infections. Notable biofilm- associated infections include chronic cystitis, prostatitis and catheter- and stent-associated infections (Warren, 2001). Bacterial biofilms were reported to affect 90 % of indwelling stents in patients (Reid et al., 1992). E. coli is responsible for most infections in patients with indwelling bladder catheters; 10–50 % of patients undergoing short- term catheterization develop UTI and essentially all patients with an indwelling urinary catheter in place for more than 30 days will have a UTI (Warren, 2001). Biofilm-associated bacteria are often hard to eradicate by antibiotics and a common observation is that soon after a course of antibiotic treatment the urinary tract will be Abbreviations: ABU, asymptomatic bacteriuria; SCLM, scanning con- focal laser microscopy; UPEC, uropathogenic E. coli; UTI, urinary tract infection. Microbiology (2007), 153, 1711–1719 DOI 10.1099/mic.0.2006/004721-0 2006/004721 G 2007 SGM Printed in Great Britain 1711