Biofilm Mediated Calculus Formation in the Urinary Tract

Mineralization and subsequent calculus formation is a common complication of biofilm infections. In the urinary tract, these infected calculi often arise from infections by urease-producing bacteria. Ammonia, liberated by bacterial urease activity, increases urine pH, resulting in the precipitation of Ca and Mg as carbonateapatite {Ca10(P04,C03MOH,C03) 2} and struvite (NH4MgP04·6Hp). These minerals become entrapped in the organic matrix which surrounds the infecting organisms and ultimately grow into mature calculi. When the causative organisms grow on urinary catheters and stents, the resulting mineralization can partially or completely obstruct urine flow. Mineralization may also exacerbate tissue damage, lead to a Joss of kidney function, and aid in the dissemination of microorganisms into deeper tissues. Several factors influence mineral formation and growth during struvite urolithiasis. These include host factors such as urine chemistry and anatomy of the urinary tract, the presence and characteristics of any foreign objects such as catheters, and bacterial factors such as the type of organisms present and their virulence factors. This review will address these and other factors which influence biofilm mineralization and calculus formation in the urinary tract.