Intestinal microbiota promote enteric virus replication and systemic pathogenesis

Abstract

Intestinal bacteria aid host health and limit bacterial pathogen colonization. However, the influence of bacteria on enteric viruses is largely unknown. We depleted the intestinal microbiota of mice with antibiotics before inoculation with poliovirus, an enteric virus. Antibiotic-treated mice were less susceptible to poliovirus disease and supported minimal viral replication in the intestine. Exposure to bacteria or their N-acetylglucosamine-containing surface polysaccharides, including lipopolysaccharide and peptidoglycan, enhanced poliovirus infectivity. We found that poliovirus binds lipopolysaccharide, and exposure of poliovirus to bacteria enhanced host cell association and infection. The pathogenesis of reovirus, an unrelated enteric virus, also was more severe in the presence of intestinal microbes. These results suggest that antibiotic-mediated microbiota depletion diminishes enteric virus infection and that enteric viruses exploit intestinal microbes for replication and transmission.

Fig. 1

Poliovirus pathogenesis, shedding, and replication in microbiota-depleted mice. (A) Bacterial loads in feces. PVRtg-Ifnar1-/- mice (n=4-7) were untreated, antibiotic-treated (Abx) for 10 days, or antibiotic-treated for 8 days and recolonized for 2 days with fecal bacteria (Abx+recol). Feces were plated and grown anaerobically, yielding colony-forming units (CFU) per milligram of feces. (B) Survival of PVRtg-Ifnar1-/- mice orally inoculated with poliovirus (untreated: n=30, Abx: n=26, Abx+recol: n=8). *p=0.012, Log-rank test. (C) Survival of PVRtg-Ifnar1-/- mice intraperitoneally inoculated with poliovirus (n=10 mice each). (D) Poliovirus shedding from PVRtg-Ifnar1-/- mice. Mice were orally inoculated with poliovirus, feces were collected (n=2-26 per interval), and poliovirus was isolated and quantified by plaque assay, yielding plaque-forming units (PFU) per milligram of feces. (E,F) Poliovirus replication in intestinal tracts of PVRtg-Ifnar1-/- (E) or PVRtg (F) mice orally inoculated with light-sensitive poliovirus (n=3-9 mice per interval). Feces were harvested, and virus was quantified +/- light exposure to determine percent replication. Symbols represent mean + SEM, *p<0.05, **p<0.01, Student's t-test. N=2-6 for all experiments.

Fig. 2

The effects of antibiotic treatment on poliovirus replication and pathogenesis. (A) Poliovirus replication kinetics in MEFs and HeLa cells +/- antibiotics. (B) Fecal bacterial loads from untreated or antibiotic-treated mice harboring antibiotic-resistant (abxR) bacteria. Feces were plated on rich medium +/- four antibiotics. (C) Survival of PVRtg-Ifnar1-/- mice orally inoculated with poliovirus pre-mixed with four antibiotics (Untreated+abx PV, n=9) or poliovirus alone in antibiotic-treated mice harboring AbxR bacteria (Abx+abxR, n=8). (Results from untreated and antibiotic-treated mice are from Fig. 1B.) (D) Replication of light-sensitive poliovirus in untreated mice receiving poliovirus+antibiotics inoculum and antibiotic-treated mice harboring abxR bacteria in comparison to antibiotic-treated mice. (Results from antibiotic-treated mice are from Fig. 1E.) Each symbol represents mean + SEM. A and B, N=2-5 experiments, C and D are from a representative experiment.

Fig. 3

Reovirus pathogenesis in microbiota-depleted mice. (A) PVRtg-Ifnar1-/- mice were either uninfected, untreated (n=5) or antibiotic-treated (n=5), or infected perorally with reovirus, untreated (n=13) or antibiotic-treated (n=15). Feces were collected 24 hours post-inoculation. (B) Fecal pathology (Table S1). (C) Upper (top) and lower (bottom) small intestines were harvested from untreated and antibiotic-treated PVRtg-Ifnar1-/- mice on day 4 post-infection or from uninfected mice. Arrows indicate Peyer's patches. (D) Quantification of Peyer's patch sizes (from C) from uninfected and infected mice. (E) Reovirus titers from day 4 post-infection PVRtg-Ifnar1-/-mouse tissues. Plaque assays were performed using murine L929 cells, yielding PFU per milligram of tissue. For B-E, n=4-9 untreated mice, n=2-9 antibiotic-treated mice. Each symbol or bar denotes the mean + SEM. *p<0.05, **p<0.01, Student's t-test. Scale bars in A and C=5mm. A and C, representative of 3-5 experiments; N=2-4 for B, D, and E.

Figure 4

Effects of bacteria and polysaccharides on poliovirus. (A) Strategy for in vitro poliovirus infectivity experiments. (B) Poliovirus recovered after incubation in PBS. (C) Poliovirus infectivity following exposure to PBS, feces, or feces supplemented with Bacillus cereus or lipopolysaccharide (LPS) (6 hours/37°C). (D) Poliovirus infectivity after exposure to medium (DME) or bacterial strains (10⁷, 10⁸, or 10⁹ CFU) (6 hours/37°C). (E) Poliovirus infectivity after incubation with compounds (1 mg/ml) (6 hours/42°C). (F) Poliovirus infectivity after incubation with various concentrations of compounds (6 hours/42°C). (G) Poliovirus binding to LPS. Poliovirus was incubated +/- biotinylated LPS for 1 hour at 37°C. A monomeric avidin column was loaded with samples and washed with PBS to collect fractions 1-6. Excess biotin was added to elute (fractions 7-12). Poliovirus was quantified yielding PFU per fraction, p<0.0001, 2-way ANOVA. (H) Binding of radiolabeled poliovirus to HeLa cells. ³⁵S-labeled poliovirus was incubated with PBS or 10⁸ CFU B. cereus for 1 hour at 37°C. An equal volume of PBS or B. cereus was added followed by immediate incubation with HeLa cells. After washing, cell-associated radioactivity was quantified. For all experiments, N=2-8 and bars and symbols denote mean + SEM, *p<0.05, **p<0.01, Student's t-test.