Microbiota encoded fatty-acid metabolism expands tuft cells to protect tissues homeostasis during Clostridioides difficile infection in the large intestine.

Metabolic byproducts of the intestinal microbiota are crucial in maintaining host immune tone and shaping inter-species ecological dynamics. Among these metabolites, succinate is a driver of tuft cell (TC) differentiation and consequent type 2 immunity-dependent protection against invading parasites in the small intestine. Succinate is also a growth enhancer of the nosocomial pathogen Clostridioides difficile in the large intestine. To date, no research has shown the role of succinate in modulating TC dynamics in the large intestine, or the relevance of this immune pathway to C. difficile pathophysiology. Here we reveal the existence of a three-way circuit between commensal microbes, C. difficile and host epithelial cells which centers around succinate. Through selective microbiota depletion experiments we demonstrate higher levels of type 2 cytokines leading to expansion of TCs in the colon. We then demonstrate the causal role of the microbiome in modulating colonic TC abundance and subsequent type 2 cytokine induction using rational supplementation experiments with fecal transplants and microbial consortia of succinate-producing bacteria. We show that administration of a succinate-deficient Bacteroides thetaiotaomicron knockout (Δfrd) significantly reduces the enhanced type 2 immunity in mono-colonized mice. Finally, we demonstrate that mice prophylactically administered with the consortium of succinate-producing bacteria show reduced C. difficile-induced morbidity and mortality compared to mice administered with heat-killed bacteria or the vehicle. This effect is reduced in a partial tuft cell knockout mouse, Pou2f3+/-, and nullified in the tuft cell knockout mouse, Pou2f3-/-, confirming that the observed protection occurs via the TC pathway. Succinate is an intermediary metabolite of the production of short-chain fatty acids, and its concentration often increases during dysbiosis. The first barrier to enteric pathogens alike is the intestinal epithelial barrier, and host maintenance and strengthening of barrier integrity is vital to homeostasis. Considering our data, we propose that activation of TC by the microbiota-produced succinate in the colon is a mechanism evolved by the host to counterbalance microbiome-derived cues that facilitate invasion by intestinal pathogens.

Commensal antimicrobial resistance mediates microbiome resilience to antibiotic disruption.

Despite their therapeutic benefits, antibiotics exert collateral damage on the microbiome and promote antimicrobial resistance. However, the mechanisms governing microbiome recovery from antibiotics are poorly understood. Treatment of Mycobacterium tuberculosis, the world's most common infection, represents the longest antimicrobial exposure in humans. Here, we investigate gut microbiome dynamics over 20 months of multidrug-resistant tuberculosis (TB) and 6 months of drug-sensitive TB treatment in humans. We find that gut microbiome dynamics and TB clearance are shared predictive cofactors of the resolution of TB-driven inflammation. The initial severe taxonomic and functional microbiome disruption, pathobiont domination, and enhancement of antibiotic resistance that initially accompanied long-term antibiotics were countered by later recovery of commensals. This resilience was driven by the competing evolution of antimicrobial resistance mutations in pathobionts and commensals, with commensal strains with resistance mutations reestablishing dominance. Fecal-microbiota transplantation of the antibiotic-resistant commensal microbiome in mice recapitulated resistance to further antibiotic disruption. These findings demonstrate that antimicrobial resistance mutations in commensals can have paradoxically beneficial effects by promoting microbiome resilience to antimicrobials and identify microbiome dynamics as a predictor of disease resolution in antibiotic therapy of a chronic infection.

Evaluation of the Nova Vet Meter for sheep-side monitoring of ß-hydroxybutyric acid (BHBA) and description of ewe BHBA during late gestation in three flocks from the Northeastern U.S.

Prevention of metabolic diseases in small ruminants may improve production efficiency and profitability, yet ewes carrying multiples or who are in poor body condition are at increased susceptibility to develop ketosis. This study evaluated the hand-held Nova Vet Meter to accurately detect ß-hydroxybutyric acid (BHBA) concentrations in ewes and determined the percentage of ewes at moderate (0.8 to 1.5 mmol/L BHBA) and greatest (≥1.6 mmol/L BHBA) risk to develop ketosis during late gestation. To validate the Nova Vet Meter, BHBA concentrations of 104 paired blood samples were measured using the Nova Vet Meter and gold-standard laboratory analysis. Receiver operating characteristics were calculated. The accuracy and sensitivity of detecting BHBA concentrations at 0.8 to 1.5 mmol/L were 94.2% and 97.3%, respectively. The accuracy and sensitivity of detecting BHBA concentrations ≥ 1.6 mmol/L were 98.0% and 50.0%, respectively. Ewe body weight (BW), body condition score (BCS), and BHBA of 117 ewes from three flocks were determined weekly during the four weeks before parturition. During the last three weeks of gestation >20% of ewes were identified with moderate risk to develop ketosis. During the last four weeks of gestation, ewes carrying triplets had reduced BCS (P = 0.0002) and increased BHBA concentrations (P < 0.0001) compared with singleton and twin pregnancies. Ewe BHBA did not correlate with lamb birth weight (R2 = 0.003; P = 0.41). In conclusion, the Nova Vet Meter is suitable for sheep-side BHBA monitoring between 0.8 and 1.5 mmol/L, but further testing is necessary to evaluate BHBA readings ≥1.6 mmol/L.