Evidence of bacterial imprints in different types of non-struvite kidney stones.

Background: Recent studies of renal lithiasis identified bacterial imprints in apatite phosphate stones and mixed calcium oxalate/apatite phosphate stones, neither of which contained struvite.

Methods: This cross-sectional observational study examined 903 stones that were collected from 844 patients during the course of 1 year. All stones were initially examined by stereoscopic microscopy. Stone fragments were then examined by scanning electron microscopy + microanalysis by X-ray dispersive energy and by Fourier-transform infrared spectroscopy. When bacterial imprints were detected, biochemical and bacteriological analysis of the patient's urine was performed.

Results: We found 8 renal stones that had bacterial imprints but no struvite. All 8 stones contained hydroxyapatite, and the imprints were located in this region. Five stones contained hydroxyapatite as the major component, two stones were mixed hydroxyapatite/calcium oxalate dihydrate stones, one was a papillary calcium oxalate monohydrate stone in which bacterial imprints were located at Randall's plaque and the other was a cavity calcium oxalate monohydrate stone that contained hydroxyapatite in the central core with bacterial imprints.

Conclusions: We identified bacterial imprints in different types of renal stones that lacked struvite, including papillary stones, and these imprints were always present in a hydroxyapatite matrix. Notably, a urinary pH above 6.0 favors the formation of apatite phosphates and the growth of bacteria. Our findings point to the importance of controlling urinary pH to prevent bacteria-mediated calculogenic processes. Background: Not applicable.