In the present study, we tested the hypothesis that oxalate homeostasis in rats might be influenced not so much by the quantity of ODB in the intestine microbiota as by the total ability of ODB to degrade oxalate (ODA rate). We assumed that due to its synergistic effect (probiotic and prebiotic), the synbiotic can restore antibiotic-induced disturbance of oxalate homeostasis in rats. To this end, we separately evaluated the changes in the ODB number and their total ODA in fecal microbiota at two-time points after ceftriaxone and synbiotic exposure. In addition, we assessed the interaction between ODB, total fecal ODA, and plasma and urine oxalate concentrations in rats.
There are several new and unexpected findings in the study. First, treatment with ceftriaxone resulted in significant growth in the ODB number on day 1 after the treatment withdrawal, and despite the increase in the ODB quantity, the ceftriaxone exposure substantially reduced total fecal ODA compared to synbiotic-treated and vehicle-treated groups. Moreover, total fecal ODA in ceftriaxone-treated rats remained the lowest in 8 weeks (on day 57) following the treatment, although the ODB number was similar in all the experimental groups. Second, the use of synbiotic did not increase the ODB number as much as enhancing their ability to degrade oxalates even when used simultaneously with ceftriaxone, which led to a significant decrease in UOx excretion. Third, ODB number was associated neither with their total ODA in fecal microbiota nor UOx excretion and POx concentration in rats. According to our results, only total fecal ODA was associated with urine and plasma oxalate levels.
The direct link between antibiotics exposure and KSD formation has been previously postulated, mainly in the context of the loss of O. formigenes in the gut microbial community [1, 5, 14, 15], the sensitivity of O. formigenes strains to commonly prescribed antibiotics , or the effect of probiotic interventions . However, in addition to O. formigenes, to date, ODA has been identified in many other representatives of the intestinal microbiota (Enterococcus spp., Lactobacillus spp., Bifidobacterium spp., Bacillus spp) [6–9, 24]. Nevertheless, the majority of published studies have been focused not on the ODB profile but differences in the general gut microbial composition between KSD patients and healthy control [2, 18].
To the best of our knowledge, this report is the first to evaluate the total ODB number and their ODA in rats’ fecal microbiota in response to ceftriaxone and synbiotic exposure. Surprisingly, according to our findings, the total ODB number was significantly increased after ceftriaxone exposure compared to vehicle- and synbiotic-treated groups. This result is in line with the recent work conducted by R. Chakraborty et al., in which the authors demonstrated a ceftriaxone-induced transient increase in the abundance and extraintestinal dissemination of Enterococcus spp and Lactobacillus spp. in a mouse model . In another recent study, the authors have observed a substantially increased relative abundance of Enterococcus spp., Lactobacillus spp. and Bifidobacterium spp. after the use of a combination of four antibiotics (bacitracin, meropenem, neomycin and vancomycin) in mice . From our point of view, these observations might be a consequence of the resistance of certain species of ODB to ceftriaxone, or it could be associated with the growth of some commensals due to ceftriaxone-induced loss of others. In this context, it is logical to assume a compensatory increase in ODB with a lesser ability to degrade oxalate, which could explain a significant decrease in total fecal ODA simultaneously with a transient increase in the ODB number in the ceftriaxone-treated rats. However simultaneous studies on the ODB number and their total functional ability to degrade oxalate have never been conducted before, hence the obtained results cannot be directly compared with the results of previous reports. Accordingly, the phenomena of ceftriaxone-induced increasing ODB number and a simultaneous decrease in their total ODA in fecal microbiota raises many questions that require further investigations.
Numerous in vitro studies have addressed the beneficial effect of probiotics on the oxalate-degrading capacity of gut microbiota and reducing hyperoxaluria [5, 11]. Clinical results are not as encouraging and need further large-scale studies [18, 28]. It should be noted that only a few studies were conducted to investigate the synbiotics effect on human health [18, 19] and the only one addressed the effects of prebiotic and synbiotic on oxalate degradation in vitro . Moreover, there are limited data concerning the interaction between antibiotics and synbiotics . Thus, it is not well understood how synbiotics alter antibiotic-induced oxalate homeostasis imbalance and whether the synbiotic supplementation changes the short-term or long-term effects of antibiotics.
The commercially available synbiotic selected for our study has never been studied before for restoration of oxalate homeostasis. However, classically, in addition to 7 strains of live probiotic microorganisms, it consisted of selenium, oligofructose and inulin as a prebiotic supplement which justified our choice. Moreover, this synbiotic was able to degrade 69% oxalate after 48 h incubation in highly selective Oxalate Medium vs other tested three probiotic supplements. It is somewhat surprising that the synbiotic exposure did not affect the ODB number but more than doubled the total fecal ODA in 2 weeks of its administration. Even with antibiotic therapy, the use of the synbiotic led to an increase in total fecal ODA, which was reflected in a significant decrease in oxaluria on day 1 after treatment withdrawal. At the end of the experiment, the number of ODB increased compared to the first measurement only in the synbiotic group. Interestingly, the synbiotic administration preserved total ODA in the fecal microbiota of ceftriaxone-treated rats during the all post-antibiotic period independently of the ODB number. In fact, on the 57th day following the treatment, the beneficial effect of enhancing total fecal ODA in the group treated simultaneously with ceftriaxone and synbiotic was almost the same as in the isolated synbiotic-treated group. In parallel with our results, A. Jačan et al have demonstrated that the synbiotic per se did not influence the gut microbiota but was able to modulate the antibiotic-induced dysbiosis in a time-dependent manner . Our data are also consistent with the findings obtained by Ö. Darilmaz et alin their in vitro study. The authors have shown that the probiotic in a combination with inulin enhanced the degradation of oxalates, thereby highlighting inulin's key role . Moreover, in line with our results, they have not found an association between oxalate degradation rate and bacterial growth after synbiotic exposure . In our opinion, the growth of ODB in our synbiotic-treated group reflects intestinal colonization of the microorganisms present in the synbiotic. In the case of simultaneous use of ceftriaxone, the changes in the ODB number resulted from the growth of enterobacteria and other pathogens, while lacto- and bifidobacteria, stimulated by prebiotic additives, modulated the activity and viability of other intestinal microbiota. These results could explain why not the abundance of ODB but rather their total ODA in fecal microbiota was associated with UOx excretion and POx concentration in the rats. Therefore, the synbiotic administration should not be considered as substitution therapy in KSD patients but as a way of providing conditions for the restoration of the intestine biocenosis and stimulation of ODB activity.