Evaluation of Biofilm Induced Urinary Infection Stone Formation in a Novel Laboratory Model System

Infection stones, which comprise approximately 15% of all urinary tract stones, are induced by infection with urease-positive pathogens. The bacteria in the stone matrix present significant treatment impediments compared to metabolic kidney stones. While much is known about how urinary composition regulates metabolic stone formation, there is a general lack of knowledge of which urinary factors regulate the rate of infection stone formation. Unfortunately more in-depth research into infection stones is limited by the lack of suitable models for real-time study of bacterial biofilm formation and stone formation under varying conditions.

We developed an in vitro model to study infection stone formation. The model closely represents the processes that occur in vivo, including the observed migration of ureolytic bacteria (our culture of Proteus mirabilis) from the bladder to the kidneys, followed by biofilm and stone formation in the kidney. We used scanning electron and confocal laser microscopy, x-ray diffraction, biological counts and dissolved chemical analyses to evaluate the model system.

Crystals that formed in the system resembled clinically removed struvite stones in structure and composition. Results showed that the degree of ureolysis required to significantly change urine pH was minimal, bacterial communities inhabited the ureter, and upstream colonization and struvite formation required lag time.

These results have implications for the detection and treatment of struvite stones. Currently this model is being used to study specific urinary factors that regulate struvite formation to identify treatment options, which combined with antibiotics would improve treatment of these stones and decrease recurrence.