Biofilm exclusion of uropathogenic bacteria by selected asymptomatic bacteriuria Escherichia coli strains

Abstract

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. INTRODUCTIONUrinary 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 infections 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, biofilmassociated infections have a major impact on permanent and temporary artificial implants placed in the human body, often with devastating con...

Mellowing Out: Adaptation to Commensalism by Escherichia coli Asymptomatic Bacteriuria Strain 83972

“…It is interesting that in our hands, strain 83972, which has been shown to inhibit UT colonization by uropathogens (70,71), was able to outperform the UPEC strain CFT073 completely with respect to biofilm formation in a flow cell system (14,18,19). Furthermore, it was also demonstrated that strain 83972 was able to exclude UPEC strains during biofilm formation in human urine (14). The excellent biofilm-forming faculty of strain 83972 might also contribute to its ability to outcompete other microbes and to inhibit UT infection and catheter colonization by uropathogens.…”

“…Meanwhile, in recent studies, we found that biofilm formation in human urine seems to be inversely related to urovirulence (14,18). Indeed, the biofilm-forming capacity of strain 83972 (and other selected ABU strains) was markedly superior to that of the UPEC group.…”

“…Furthermore, the global gene expression profile comparison of 83972 in humans and CFT073 in mice revealed some similarities; both strains grow rapidly in the UT, as indicated by the upregulation of genes involved in the translational machinery, and respond to iron limitation by the activation of genes related to iron acquisition. Meanwhile, in spite of its inability to express virulence factors in urine, strain 83972 is able to outperform strain CFT073 with respect to both growth and biofilm formation in urine (14,18,57).…”

Transposon Mutagenesis Identifies Uropathogenic Escherichia coli Biofilm Factors

“…In the urinary tract, biofilm formation can lead to several serious infections, not only in catheterized patients but also in nonhospitalized individuals (21,68). Eighty-five percent of community-acquired urinary tract infections (UTI) and 50% of device-associated UTI are caused by uropathogenic Escherichia coli (UPEC) (24), which employ a complex pathogenic cascade in the urinary tract, occupying extracellular and intracellular niches during the course of infection (60).…”

Virulence Traits in Escherichia Coli Strains Isolated from Outpatients with Urinary Tract Infections

“…Quantification of biofilm production in polystyrene microtiter plates (U-bottom; Falcon Becton Dickinson) was based on the method described by Ferrieres et al (27). After 48 h incubation at 37°C the ability of the strains to adhere to the plates was tested by I% crystal violet staining.…”