Struvite Stone Formation by Ureolytic Biofilm Infections
This chapter describes how urinary tract infections can lead to stone formation. The most frequent type of infection stone is struvite (MgNH4PO4 · 6H2O), although it is common that struvite stones and infections are associated with other stone types, often forming large staghorn calculi. A complete understanding of struvite stone formation requires knowledge of the pathogen biology, including metabolic activity and motility, as well as a basic understanding of how minerals form.
The pathogens responsible for struvite stones are those that break down urea into ammonium (NH4+) and inorganic carbon. This reaction, known as ureolysis, increases the pH of urine and the concentration of NH4+, thus increasing the saturation index of struvite. If supersaturation is reached, i.e. the ion activity product (IAP) is greater than the ion activity product at equilibrium (Ksp), struvite stone formation is possible.
An important consideration with urinary tract infections is that pathogens often form attached communities, known as biofilms, which help them to survive physical and chemical stresses. Not only are biofilm-related infections more difficult to treat, but they can facilitate stone formation by creating gradients in chemical concentrations near surfaces. Modern laboratory bioreactors and computer models, described in this chapter, are improving our understanding of how and why infection stones such as struvite form. Current treatment options for infection stones can be painful or ineffective. As more is learned about the complex microbe-fluid-mineral interactions, less-invasive treatments and more-effective prevention strategies will be developed.
KeywordsUrinary Tract Infection (UTI) Struvite Urolithiasis Saturation Index Biofilm Ureolysis Reactive Transport Modeling Geochemical Equilibrium Modeling
This work was supported by the National Science Foundation through NSF award DMS-0934696. James Connolly was also supported by a NSF-IGERT fellowship in Geobiological Systems at Montana State University (DGE-0654336). Trace Hobbs was supported by a Howard Hughes Medical Institute Scholarship through Montana State University.
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