Strontium ranelate enriched Ruminococcus albus in the gut microbiome of Sprague-Dawley rats with postmenopausal osteoporosis.

BACKGROUND: Gut microbiome is critical to our human health and is related to postmenopausal osteoporosis (PMO). Strontium ranelate (SrR) is an anti-osteoporosis oral drug that can promote osteoblast formation and inhibit osteoclast formation. However, the effect of SrR on gut microbiome has been rarely studied. Therefore, we investigated the effect of oral SrR on gut microbiome and metabolic profiles. RESULTS: In this study, we used ovariectomized (OVX) Sprague-Dawley rats to construct a PMO model and applied oral SrR for 6 weeks. The relative abundance of intestinal microbiome was investigated by 16S rRNA metagenomic sequencing. Ultra-high-performance liquid chromatography-mass spectrometry (UHPLC-MS) was used to analyze changes in metabolites of intestinal contents. Results demonstrated that 6-week oral SrR alleviated osteoporosis and significantly changed the composition of the gut microbiome and metabolic profiles of OVX rats. Ruminococcus, Akkermansia and Oscillospira were significantly enriched in the gut of OVX rats after 6-week oral SrR. Especially, the species R. albus showed the greatest importance by a random forest classifier between OVX and OVX_Sr group. The enrichment of R. albus in the gut was positively correlated with bone mineral density and the accumulation of lycopene and glutaric acid, which also significantly elevated after oral SrR. CONCLUSIONS: We discovered that oral SrR can improve bone health while stimulate the accumulation of gut microbe R. albus and metabolites (lycopene and glutaric acid). The results suggested possible connections between oral SrR and the gut-bone axis, which may provide new insight into the treatment/prevention of osteoporosis.

KbvR mutant of Klebsiella pneumoniae affects the synthesis of type 1 fimbriae and provides protection to mice as a live attenuated vaccine.

Klebsiella pneumoniae is a leading cause of severe infections in humans and animals, and the emergence of multidrug-resistant strains highlights the need to develop effective vaccines for preventing such infections. Live attenuated vaccines are attractive vaccine candidates available in the veterinary field. We recently characterized that the K. pneumoniae kbvR (Klebsiella biofilm and virulence regulator) mutant was a highly attenuated strain in the mice model. In the present study, the characterization, safety, and protective efficacy of ΔkbvR strain as a live attenuated vaccine were evaluated. The synthesis and activity of type 1 fimbriae were increased in the ΔkbvR strain. All mice inoculated by the subcutaneous route with 105, 106, and 107 colony-forming units (CFU) doses of the ΔkbvR strain survived. Subcutaneous immunization with two doses of 105 or 107 CFU ΔkbvR elicited a robust humoral immune response, and provided protection against the following K. pneumoniae intraperitoneal infection. The antisera of mice immunized with 105 CFU dose improved the opsonophagocytic ability and complement-mediated lysis not only to the same serotype strain but also to the different serotype strain. The passive transfer of antisera from 105 CFU dose-immunized mice provided protection against K. pneumoniae infection. Overall, our results suggest the great potential of the ΔkbvR strain as a novel vaccine candidate against K. pneumoniae infections in herds or humans.

High Osmotic Stress Increases OmpK36 Expression through the Regulation of KbvR to Decrease the Antimicrobial Resistance of Klebsiella pneumoniae.

Klebsiella pneumoniae is a pathogen known for its high frequency of antimicrobial resistance. Responses to various environmental stresses during its life can influence the resistance to antibiotics. Here, we demonstrate the role and mechanism of KbvR regulator in the response to environmental osmotic stress and in the effect of osmotic stress on antimicrobial resistance. The kbvR mutant strain exhibited increasing tolerance to high osmotic stress and certain antibiotics, including ß-lactams. The expression levels of KbvR and outer membrane porin OmpK36 were upregulated in response to high osmotic stress in the wild type (WT), and the deletion of kbvR decreased the expression level of ompK36. The membrane permeability of the kbvR mutant strain was decreased, which was partly restored through the upregulated expression of OmpK36. The DNA affinity purification sequencing (DAP-seq) and microscale thermophoresis (MST) assay disclosed the binding of KbvR to the promoter of the ompK36 gene, indicating that KbvR directly and positively regulated the expression of OmpK36. The high osmotic stress increased the susceptibility to ß-lactams and the expression of ompK36 in the WT strain. However, the increased ompK36 expression and the susceptibility to ß-lactams in the kbvR mutant strain under high osmotic stress were lower than those of WT. In conclusion, our study has identified that high osmotic stress in the environment influenced the resistance of K. pneumoniae to antibiotics and that the regulation of KbvR with OmpR on the expression of OmpK36 was involved in countering high osmotic stress to change the antimicrobial resistance. IMPORTANCE Klebsiella pneumoniae is considered a global threat because of the rising prevalence of multidrug-resistant strains and their optimal adaptation to clinical environments and the human host. The sensing and adaption abilities of bacteria to the environmental osmotic stress can change the expression of their outer membrane porins, membrane permeability, and resistance to antibiotics. This study reports that KbvR is a newly found regulator that can be upregulated under high osmotic stress and directly regulate the expression of OmpK36 to change the resistance of K. pneumoniae to ß-lactam antibiotics. The results demonstrate how adaptation to high osmotic stress changes the sensitivity of K. pneumoniae to antibiotics. The mechanism can be used to sensitize bacteria to antibiotics and highlight new potential strategies for exploiting shared constraints in governing adaptation to diverse environmental challenges.