Struvite (MgNH₄PO₄·6H₂O) and carbonate apatite (Ca₁₀(PO₄)₆CO₃; CA) are the major components of infectious urinary stones. They are formed when the urinary tract is infected by urease positive microorganisms, mainly from Proteus sp. This kind of stones constitutes from 10% [1] to 30% [2] of all urinary stones. One of the most frequently used treatment procedures for urinary stones is extracorporeal shock wave lithotripsy and a long-term antibiotic treatment. Such a treatment should prevent also the recurrence and re-growth of stone after treatment. However, it is known that even bacterial substances and dead bacteria may serve as sites for heterogeneous nucleation and re-crystallization. Among other things, this is the reason that the recurrence after treatment is on the level of 50%. Therefore, in recent years, many studies on the crystallization processes have been made for providing effective treatment methods.

Fig. 1. Struvite crystals (1) and CA precipitation grown from artificial urine (a) in the absence of disodium EDTA and (b) in the presence of disodium EDTA (5 mM).    
Scale bar: ­­­­50 μm.

In the present research we study the effect of disodium EDTA on the crystallization of struvite and CA. The growth of struvite crystals and CA occurred in the solution of artificial urine at 37^oC. Mineral components in the artificial urine correspond to mean concentration found in 24-hour period in normal human urine. The crystallization process occurs after consecutive addition of aqueous ammonia solution to mimic urease activity under the control of pH value. Such an addition emulates real urinary tract infection [3]. The results demonstrate a clear relationship between disodium EDTA concentration and struvite crystallization and CA precipitation. Increasing the disodium EDTA concentration causes an increase in induction time and decrease in the growth efficiency (Fig. 1) compared to baseline (without disodium EDTA). Increasing the concentration of disodium EDTA reduces the mass of struvite and CA formed in the solution of artificial urine. Additionally, the struvite crystals are found to decrease, while the aspect ratio is found to increase in the presence of disodium EDTA. The results indicate that by dosing an appropriate concentration of disodium EDTA struvite and CA precipitation in artificial urine can be lowered or even prevented. The appropriate dose of disodium EDTA required preventing struvite nucleation and CA precipitation is predictable taking into account the pH of the solution of urine and the magnesium and calcium concentration.

References

[1] Bichler, K.H.; Eipper, E.; Naber, K.; Braun, V.; Zimmermann, R.; Lahme, S. Int. J. Antimicrob. Agents  2002, 19, 488–498.

[2] Chauhan, Ch.K.; Joshi, M.J.  J. Cryst. Growth 2013, 362, 330–337.

[3] Prywer, J.; Torzewska, A.; Evidence-Based Complementary and Alternative Medicine, vol. 2012, Article ID 862794, 7 pages, 2012.

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