Urolithiasis remains a pressing medical and social problem nowadays. In Ukraine, the prevalence of urolithiasis ranks second, among all urological diseases, after urinary tract infection. The course of the disease is characterized by the phenomena of acute and chronic pyelonephritis, frequent recurrences of urolithiasis (30-80%), which in turn leads to renal failure, disability and mortality. Therefore, the search for effective methods of treatment and prevention of this disease based on a deeper understanding of its pathogenetic mechanisms is becoming increasingly important. Oxalate nephrolithiasis (the presence of oxalate stones in the urinary tract) is observed in 50-70% of patients with urolithiasis. Hyperoxaluria (excess urinary oxalate excretion more than 50 mg/day) is a major risk factor for oxalate nephrolithiasis. Normally, 85% to 90% of oxalate in the body is the end product of the metabolism of glyoxylic and ascorbic acids in the liver (endogenous oxalate), the remaining 10%-15% of blood oxalate is absorbed in the intestine (exogenous oxalate).
Due to the fact that the degradation of oxalate in mammals occurs due to the formyl-CoA transferase and oxalyl-CoA decarboxylase enzymes of the intestinal normobiota, one of the promising areas of treatment and prevention of oxalate nephrolithiasis is a deeper understanding of the correlation relationships between total oxalate-degrading activity of fecal biopsy and endogenous oxalate homeostasis in normal and renal malformations, as well as the selection of bacteria with pronounced oxalate-degrading activity as potential probiotic strains for the prevention and treatment of hyperoxaluria.
Oxalate-degrading bacteria (ODB) are divided into obligate (use oxalate as the sole source of energy: Oxalobacter formigenes) and facultative (use oxalate as an alternative or additional source of energy: Enterococcus spp., Lactobacillus spp., Bifidobacterium spp., Bacillus spp.) oxalotrophs. Oxalotrophs were detected by plating 10-fold dilutions of fecal biopsy on a highly selective Oxalate Medium (Na2C2O4 as a single energy source). Obligate and facultative oxalotrophs were isolated by subculturing colonies from Oxalate Medium on MRS-agar, Bifidobacterium-agar or MPA. Inability of obligate oxalotrophs to grow on these media was taken into account. The affiliation of obligate oxalotrophs to the O. formigenes species was confirmed using PCR analysis. Under normal physiological conditions the largest number of obligate oxalotrophs was isolated in Wistar rats (lg 6.12 ± 0.63 CFU/g). In other studied groups (nonlinear rats, BalbC mice, chinchilla rabbits) the quantity ranged within lg 2.1±0.4 – 2.97±0.25 CFU/g. The number of facultative oxalotrophs was almost the same in all studied groups of animals.
Given the fact that a diet enriched with oxalate-containing products is considered one of the main pathogenetic factors in the development of hyperoxaluria, we examined the effect of oxalate diet on the amount of ODB. Daily addition of 2 mg/kg Na2C2O4 to the diet of nonlinear rats for 14 days resulted in a statistically significant increase in the number of obligate oxalotrophs and a decrease in the number of facultative oxalotrophs in the fecal biopsy (P <0.05).
Administration of antibacterial drugs (ceftriaxone (300 mg/kg, і.m.) for 7 days or oral combination of ampicillin (75 mg / kg) with metronidazole (50 mg/kg) for 3 days resulted in 100% inhibition of the growth of obligate oxalotrophs and statistically significant reduction in the number of facultative oxalotrophs in the fecal biopsy of Wistar rats, even after 56 days of drug withdrawal. This confirmed the role of antibiotic therapy as one of the key triggers in the development of hyperoxaluria.
Due to the fact that the presence of obligate oxalotrophs is individual, while the function of oxalate degradation can be performed by facultative oxalotrophs, it can be concluded that the absence of obligate oxalotrophs in fecal biopsy can not be an objective prognostic criterion for the risk of hyperoxaluria development. We suggested that it is more appropriate to assess the activity of ODB, not their number. In order to solve the issue, we tested the methodological adequacy and financial relevance of known methods of oxalate levels detection, including gas chromatography, fluorescence spectrometry and redox titration with KMnO4, for studying total oxalate-degrading activity of bacteria (ODA) of fecal biopsy without isolating them in pure culture.
