The impact of ibezapolstat and other Clostridioides difficile infection-relevant antibiotics on the microbiome of humanized mice.

Ibezapolstat (IBZ) is a competitive inhibitor of the bacterial Pol IIIC enzyme in clinical development for the treatment of Clostridioides difficile infection (CDI). Previous studies demonstrated that IBZ carries a favorable microbiome diversity profile compared to vancomycin (VAN). However, head-to-head comparisons with other CDI antibiotics have not been done. The purpose of this study was to compare microbiome changes associated with IBZ to other clinically used CDI antibiotics. Groups of germ-free (GF) mice received a fecal microbiota transplant from one of two healthy human donors and were subsequently exposed to either IBZ, VAN, fidaxomicin (FDX), metronidazole (MET), or no antibiotic (control). 16S rRNA encoding gene sequencing of temporally collected stool samples was used to compare the gut microbiome perturbations between treatment and no-drug control groups. Among the tested antibiotics, the most significant change in microbiome diversity was observed in MET-treated mice. Each antibiotic had a unique effect, but changes in alpha and beta diversities following FDX- and IBZ-treated groups were less pronounced than those observed in VAN- or MET-treated groups. By the end of therapy, both IBZ and FDZ increased the relative abundance of Bacteroidota (phylum), with IBZ additionally increasing the relative abundance of Actinomycetota (phylum). In microbiome-humanized mice, IBZ and FDX had smaller effects on gut microbiome diversity than VAN and MET. Notable differences were observed between the microbiome of IBZ- and FDX-treated groups, which may allow for differentiation of these two antibiotics in future studies.