The pilot clinical study presented demonstrates the possibility, safety, and effectiveness of oral microbiota transplantation from a healthy donor to a patient with neuroblastoma to prevent chemotherapy-induced oral mucositis. A 6-month-old patient with a diagnosis of retroperitoneal neuroblastoma was treated according to the NB 2004 protocol. Due to the development of severe oral mucositis, it was decided to perform oral microbiota transplantation. During the next 3 chemotherapy cycles and conditioning regimen before autologous hematopoietic cell transplantation (auto-HCT), the patient was repeatedly injected per os with donor saliva from her healthy mother. Oral microbiota transplantation was shown to effectively prevent the development of oral mucositis after chemotherapy, and only grade 1 oral mucositis developed after auto-HCT. In all loci of the oral cavity, there was a decreased abundance of bacteria from the Staphylococcaceae, Micrococcaceae, and Xanthomonadaceae families. Conversely, there was an increase in the relative abundance of Streptococcaceae and certain other bacterial taxa. In conclusion, the transplantation of maternal saliva in this patient prevented severe mucositis and was accompanied by a compositional change of the patient’s oral microbiota. No adverse events due to the transplantation of maternal saliva were noted.

Intestinal bacterial dysbiosis develops in a number of immune-mediated disorders. Fecal microbiota transfer (FMT) is considered a potentially efficient tool for restoration of the patient’s gut microbiota. The aim of our study was to trace the time course of dominant bacterial populations and some Enterobacteria phages in patients with GVHD and Crohn’s disease after FMT procedure. Patients and methods: We observed 12 patients with intestinal graft-versus-host disease (GVHD), and 15 persons with Crohn’s disease after massive anti-infectious treatment. FMT was performed by a standard protocol using oral capsules administered for 2 days. Fecal bacteriome was assessed by 16S rRNA sequencing. Viral sequences were identified by NGS with a customized primer set. Plasma citrulline levels were measured in order to assess enterocyte damage in the patients. Results: Complete clinical response to FMT was observed in 5 of 12 GVHD patients and 10 of 15 Crohn’s disease cases. Before FMT, most anaerobic Bacillota were exhausted in both Crohn’s disease patients and GVHD. Following FMT, Akkermansia ratios tended to decrease within 30 days in Crohn’s disease, along with higher Faecalibacteria, Romboutsia, and Dialister ratios than in GVHD, thus suggesting lesser damage to anaerobic microbiota in Crohn’s disease. Increased contents of facultative anaerobes (Enterococcus and E. coli) was detected in GVHD patients after FMT. Fecal virome changes in Crohn’s disease after FMT included early transient decrease in Caudoviricetes with a rise in Lederbergvirus and Eganvirus ratios at later terms. In GVHD patients, reverse correlations were revealed between E. coli and E. coli-hosted Eganvirus species. Intestinal damage assessed by low plasma citrulline levels was associated with fecal Klebsiella expansion, being more pronounced in GVHD than in Crohn’s disease. Clinical response to FMT in GVHD patients correlated with increased plasma citrulline and lower Eganvirus abundance. Future studies will concern specific relations between fecal bacteriome and virome reconstitution following FMT in gut GVHD and other immune-mediated intestinal disorders.

Dose-intensive cytostatic therapy and antibiotic treatment in allogeneic hematopoietic stem cell transplantation (allo-HSCT) cause severe abnormalities in a composition of gut microbiota as well as the emergence of antibiotic resistance. The data on the longitudinal recovery of major bacterial phyla and the expansion of genes associated with antibiotic resistance are limited. We collected regular stool samples during the first year after allo-HSCT from 12 adult patients with oncohematological disorders after allo-HSCT and performed 16SrRNA sequencing, multiplex PCR, conventional bacteriology and CHROMagar testing. We observed a decline in Shannon microbiota diversity index as early as day 0 of allo-HSCT (p = 0.034) before any administration of antibiotics, which persisted up to 1 year after transplantation, when the Shannon index returned to pre-transplant levels (p = 0.91). The study confirmed the previously shown decline in Bacillota (Firmicutes) genera and the expansion of E. coli/Shigella, Klebsiella and Enterococci. The recovery of Firmicutes was slower than that of other phyla and occurred only a year post-transplant. A positive correlation was observed between the expansion of E. coli/Shigella genera and bla_KPC, bla_CTX-M-1 and bla_TEM (p < 0.001), Klebsiella spp. and bla_OXA-48-like, bla_NDM, bla_CTX-M-1, bla_TEM, and bla_SHV (p < 0.001), Pseudomonas spp. and bla_NDM (p = 0.002), Enterococcus spp. and bla_OXA-48-like, bla_NDM, bla_CTX-M-1, bla_SHV (p < 0.01). The correlation was observed between the expansion of Enterobacterales and and carbapenemase-positive CHROMagar samples (p < 0.001). Samples positive for carbapenem-resitant bacteria were at their maximum levels on day +30, and were gradually diminishing one year after allo-HSCT. From day +30 to +60, all isolated K. pneumoniae strains in fecal samples proved to be resistant to the main antibiotic groups (carbapenems, aminoglycosides, fluoroquinolones, third-generation cephalosporins). One year after HSCT, we documented the spontaneous decolonization of K. pneumoniae. The sensitivity of molecular biology techniques in the search for total and antibiotic-resistant Klebsiella seems to be superior to common bacteriological cultures. Future studies should be focused on searching for novel approaches to the efficient reconstitution and/or maintenance of strictly anaerobic microbiota in oncological patients.