Replication of Human Norovirus in Mice after Antibiotic-Mediated Intestinal Bacteria Depletion

Human noroviruses (HuNoVs) are the main cause of acute gastroenteritis causing more than 50,000 deaths per year. Recent evidence shows that the gut microbiota plays a key role in enteric virus infectivity. In this context, we tested whether microbiota depletion or microbiota replacement with that of human individuals susceptible to HuNoVs infection could favor viral replication in mice. Four groups of mice (n = 5) were used, including a control group and three groups that were treated with antibiotics to eliminate the autochthonous intestinal microbiota. Two of the antibiotic-treated groups received fecal microbiota transplantation from a pool of feces from infants (age 1-3 months) or an auto-transplantation with mouse feces that obtained prior antibiotic treatment. The inoculation of the different mouse groups with a HuNoVs strain (GII.4 Sydney [P16] genotype) showed that the virus replicated more efficiently in animals only treated with antibiotics but not subject to microbiota transplantation. Viral replication in animals receiving fecal microbiota from newborn infants was intermediate, whereas virus excretion in feces from auto-transplanted mice was as low as in the control mice. The analysis of the fecal microbiota by 16S rDNA NGS showed deep variations in the composition in the different mice groups. Furthermore, differences were observed in the gene expression of relevant immunological mediators, such as IL4, CXCL15, IL13, TNFα and TLR2, at the small intestine. Our results suggest that microbiota depletion eliminates bacteria that restrict HuNoVs infectivity and that the mechanism(s) could involve immune mediators.This research was funded by the Spanish Ministry of Science and Innovation (MICIN)/Spanish State Research Agency (AEI)/10.13039/501100011033 Project grants PID2020-115403RB C21 to M.J.Y. and PID2020-115403RB C22 to J.R.-D. The study was also supported by Valencian Government grant IDIFEDER/2018/056 and by European FEDER founds to J.R.-D., C.S.-B. is the recipient of a FPI predoctoral grant PRE2018-083315 by MICIN/AEI/10.13039/501100011033 and by “ESF Investing in your future”. N.P.-G. is the recipient of a predoctoral grant from the Valencian Government (ACIF/2020/085). N.N.-L. is the recipient of a predoctoral grant from the Valencian Government (ACIF/2020/076).Peer reviewe