A Microbial Model for the Formation of Calcium Oxalate and Calcium Phosphate Stones

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Project Summary/Abstract Urinary stones occur in 10% of people. The economic burden from urinary stones accounts for more than 2 billion dollars annually. Past studies have demonstrated that bacteria can be cultured from about one-third of urinary stones and we have provided the initial demonstration that DNA sequencing coupled with enhanced culture methods can be used to identify the urinary stone microbiota (the bacteria in urinary stones) in many more stones than by standard culturing alone. Yet, critical knowledge gaps exist concerning the underlying mechanisms of urinary stone pathophysiology. Alarmingly, prevalence of urinary stones is increasing, and new treatments are not being developed. Although urine supersaturated with calcium oxalate has been associated with stone formation, supersaturated urine is often present in non-stone formers. Accumulating evidence supports a bacterial role in urinary stone pathophysiology. First, bacteria aggregate to calcium oxalate (CaOx), the type of crystal responsible for most urinary stone disease. Second, initial in vitro studies indicate that bacterial flagella are important components in bacterial promotion of crystal aggregation. Third, bacteria increase the size of crystal clusters in an in vivo murine model. Our long-term research goal is to develop new urinary stone treatment strategies that reduce urinary stone recurrence. We hypothesize that flagella directly contribute to lithogenesis. To begin to determine the functional role of flagella in stone formation, we will test bacterial mutants lacking key flagella components and/or function for their ability to promote CaOx aggregation in vitro and in vivo. (Aim 1). Besides flagella, we also hypothesize that other genetic factors may contribute to lithogenesis as well. We will perform a bacteria mutant screen to identify non-flagellar genes involved in interactions with CaOx crystals. In addition, we will explore whether the identified genes are enriched in bacterial isolates associated with stones relative to urinary isolates not associated with stones (Aim 2).