Bacterial Biofilms in Patients With Indwelling Urinary Catheters

Summary and Introduction

Summary

Bacteria have a basic survival strategy: to colonize surfaces and grow as biofilm communities embedded in a gel-like polysaccharide matrix. The catheterized urinary tract provides ideal conditions for the development of enormous biofilm populations. Many bacterial species colonize indwelling catheters as biofilms, inducing complications in patients’ care. The most troublesome complications are the crystalline biofilms that can occlude the catheter lumen and trigger episodes of pyelonephritis and septicemia. The crystalline biofilms result from infection by urease-producing bacteria, particularly Proteus mirabilis. Urease raises the urinary pH and drives the formation of calcium phosphate and magnesium phosphate crystals in the biofilm. All types of catheter are vulnerable to encrustation by these biofilms, and clinical prevention strategies are clearly needed, as bacteria growing in the biofilm mode are resistant to antibiotics. Evidence indicates that treatment of symptomatic, catheter-associated urinary tract infection is more effective if biofilm-laden catheters are changed before antibiotic treatment is initiated. Infection with P. mirabilis exposes the many faults of currently available catheters, and plenty of scope exists for improvement in both their design and production; manufacturers should take up the challenge to improve patient outcomes.

Introduction

The biofilm mode of growth is a basic survival strategy deployed by bacteria in a wide range of environmental, industrial and clinical aquatic settings.^[1] Bacterial cells have a strong preference for life on surfaces rather than in planktonic suspension.^[2] These cells have an array of adhesins in their cell walls that allow them to colonize many types of substrate, and, on contact with a surface, the cells secrete exopolysaccharides that secure their attachment. The bacteria then multiply to form microcolonies of cells that subsequently spread over the surface, forming populations embedded in a gel-like polysaccharide matrix (Figure 1). The cells in these biofilm communities are protected from environmental stresses, and this protection has particular advantages for the bacteria in biofilms that develop in vivo. Microorganisms that are apparently fully sensitive to antibiotics and antiseptics in conventional laboratory testing methods become fully resistant in the biofilm mode in vivo.

Figure 1. (click image to zoom) Conceptualization of biofilm development and dynamic behaviors. The figure was compiled from laboratory and natural observations of pure-culture (both Gram-positive and Gram-negative organisms) and mixed-culture biofilms. Image courtesy of P Dirckx, Center for Biofilm Engineering, USA. Permission obtained from Nature Publishing Group © Hall-Stoodley L et al. (2004) Nat Rev Microbiol 2: 95-108.