Occurrence of Nanobacteria-Like Particles in Renal Stones of a Southern Brazilian Population

Abstract

Purpose: Identifying the source of stone formation in recurrent stone formers has always been a big problem. Material and Methods: In this study kidney stones from 52 patients were submitted to direct examination by scanning electronic microscopy (SEM) after manual fracture and 27 calculi were cultured in Eagle’s Minimum Essential Medium (E-MEM) and Brain-Heart Infusion (BHI) for eight weeks at 37°C in 5% CO<sub>2</sub> atmosphere. Twenty-seven powdered and demineralized stones were suspended in sterile PBS, filtered through 0.22 m-pore-size sterile filters Millex (Millipore, Massachusetts, USA) and submitted to DNA extraction (Quiagen-Brazil). Platinum PCR SuperMIX (GIBCO-BRL), primers (Invitrogen), and Ultra Pure Water (Advanced Biotechnologies, Columbia, MD) were used for PCR (Polymerase Chain Reaction), which was generally conducted for 30 or 35 cycles with annealing of primers for 40 sec at 55°C and extension for 1 min at 72°C. Results: In 36 out 52 (69%) kidney stones it was detected the presence of biofilm coating the mineral surface of the stone when examined by SEM, consisting of coccoid particles, isolated or clustered, with diameter of 500 nm or less. Eleven out 27 (41%) kidney stone cultures produced white-colored sediment on the bottom of the tubes after eight-week incubation, revealing tiny structures similar to those observed directly by SEM. These structures were similar in size and morphology to spherical apatite particles previously observed in human kidney stones and named as nanobacteria (NB). No PCR products were observed in the samples. Conclusion: We found a strong correlation between renal stones and calcifying nanoparticles (CNP) in this study and these results open a new insight on this area to explore the etiology of stone formation. Whether NB/CNP are truly microorganisms or self-propagating mineral compounds is still controversial and its contribution, if any, in apatite nucleation and crystal growth remains uncertain