BackgroundThe role of calcium oxalate crystals and deposits in UTI pathogenesis has not been established. The objectives of this study were to identify bacteria present in pediatric urolithiasis and, using in vitro and in vivo models, to determine the relevance of calcium oxalate deposits during experimental pyelonephritis.MethodsPediatric kidney stones and urine were collected and both cultured and sequenced for bacteria. Bacterial adhesion to calcium oxalate was compared. Murine kidney calcium oxalate deposits were induced by intraperitoneal glyoxalate injection and kidneys were transurethrally inoculated with uropathogenic Escherichia coli to induce pyelonephritisResults E. coli of the family Enterobacteriaceae was identified in patients by calcium oxalate stone culture. Additionally Enterobacteriaceae DNA was sequenced from multiple calcium oxalate kidney stones. E. coli selectively aggregated on and around calcium oxalate monohydrate crystals. Mice inoculated with glyoxalate and uropathogenic E. coli had higher bacterial burdens, increased kidney calcium oxalate deposits and an increased kidney innate immune response compared to mice with only calcium oxalate deposits or only pyelonephritis.ConclusionsIn a murine model, the presence of calcium oxalate deposits increases pyelonephritis risk, likely due to preferential aggregation of bacteria on and around calcium oxalate crystals. When both calcium oxalate deposits and uropathogenic bacteria were present, calcium oxalate deposit number increased along with renal gene transcription of inner stone core matrix proteins increased. Therefore renal calcium oxalate deposits may be a modifiable risk factor for infections of the kidney and urinary tract. Furthermore, bacteria may be present in calcium oxalate deposits and potentially contribute to calcium oxalate renal disease.

The contribution of genetic variation to urinary tract infection (UTI) risk in children with vesicoureteral reflux is largely unknown. The innate immune system, which includes antimicrobial peptides, such as the α-defensins, encoded by DEFA1A3, is important in preventing UTIs but has not been investigated in the vesicoureteral reflux population. We used quantitative real-time PCR to determine DEFA1A3 DNA copy numbers in 298 individuals with confirmed UTIs and vesicoureteral reflux from the Randomized Intervention for Children with Vesicoureteral Reflux (RIVUR) Study and 295 controls, and we correlated copy numbers with outcomes. Outcomes studied included reflux grade, UTIs during the study on placebo or antibiotics, bowel and bladder dysfunction, and renal scarring. Overall, 29% of patients and 16% of controls had less than or equal to five copies of DEFA1A3 (odds ratio, 2.09; 95% confidence interval, 1.40 to 3.11; P<0.001). For each additional copy of DEFA1A3, the odds of recurrent UTI in patients receiving antibiotic prophylaxis decreased by 47% when adjusting for vesicoureteral reflux grade and bowel and bladder dysfunction. In patients receiving placebo, DEFA1A3 copy number did not associate with risk of recurrent UTI. Notably, we found that DEFA1A3 is expressed in renal epithelium and not restricted to myeloid-derived cells, such as neutrophils. In conclusion, low DEFA1A3 copy number associated with recurrent UTIs in subjects in the RIVUR Study randomized to prophylactic antibiotics, providing evidence that copy number polymorphisms in an antimicrobial peptide associate with UTI risk.

Carbonic anhydrase 2 deficiency leads to increased pyelonephritis susceptibility.

Dear Editor, We identify that children with a history of urinary tract infections (UTIs) and vesicoureteral reflux (VUR) with low deleted in Malignant Brain Tumors 1 (DMBT1) DNA copy number have ∼4-fold higher odds of recurrent UTIs compared to those with high DMBT1 DNA copy number. With bacterial resistance to antibiotics increasing, we need to develop new strategies to guide judicious use of antibiotics such as using the patient's genetic profile. 1 Some groups, such as children with VUR, are at risk for UTIs and associated adverse outcomes. The Randomized Intervention for Children with VUR (RIVUR) study determined that antibiotic prophylaxis reduced recurrent UTIs in children with VUR but at the expense of increased resistance. 2 In a genome-wide array, we identified that DMBT1 locus was a candidate gene for genetic variation in the UTI/VUR patient population. 3 We have also shown that DMBT1 has two copy number variations which occur in scavenger receptor cysteine-rich domains (SRCR) which have bacterial agglutination capabilities. 4,5 The first CNV involves SRCR3-SRCR6 and is called DMBT1 CNV SRCR3-6 ; the other involves SRCR9-SRCR11 and is called DMBT1 CNV SRCR9-11 (Supplemental Material S1). 4 We used paralogue ratio testing to determine the absolute DMBT1 copy number in RIVUR patients. We also evaluated the biological relevance of DMBT1 in experimental UTI models of a knockout mouse (Dmbt1 −/− ). 6 Agglutination studies of uropathogenic Escherichia coli (UPEC) with recombinant DMBT1 6 kb (DMBT1 gp340 -short) or recombinant DMBT1 8 kb (DMBT1 gp340 -long) as surrogate model for the protein produced by low and high DMBT1 copy number respectively were also performed. 7 Full details about the methods may be found in Supplemental Material S2.This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.

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