2957. Decreased microbial diversity and baseline intestinal inflammation are associated with worse outcome in aged, female mice infected with Clostridioides difficile

BACKGROUND: C. difficile infection is more common and severe in people over 65-years old. Understanding the pathogenesis within the triangle of host, pathogen, and the microbiota in aged population will help decrease the disease severity. METHODS: Young (3-month-old) and aged (22 to 25-month-old) male and female C57BL/6 mice were treated with 0.5g/L cefoperazone for ten days to render them susceptible to C. difficile infection. Antibiotic-treated mice were challenged with 10(3) to 10(4) spores of C. difficile via oral gavage. Three C. difficile strains were selected for challenge. These strains vary in the severity of disease observed in young, cefoperazone-treated mice; CD630 (mild disease), R20291 (moderate), and VPI10463 (severe). Mice were monitored for weight loss and clinical signs of disease following challenge. The degree of intestinal inflammation was determined by fecal lipocalin-2 measurement. The microbiota of animals before challenge was monitored by 16S rRNA-encoding gene sequence analysis. Mouse model of C. difficile infection [Figure: see text] RESULTS: Overall, there was no significant difference in weight loss between young and aged mice following challenge. However, aged female mice lost significantly more weight than male mice when infected with C. difficile CD630 (p = 0.031) and R20291 (p = 0.0027). Microbiota analysis revealed that alpha diversity was lower in female aged mice compared to male aged mice. No sex differences were noted in young mice. Measurement of fecal lipocalin revealed that aged female mice had baseline inflammation not seen in aged male mice (p = 0.02). Finally, we found a strong negative correlation between species richness (Sobs) and maximum weight loss (R-squared=0.74) in aged mice. Lipocalin-2 levels were moderately correlated with maximum weight loss (R-squared=0.51). [Figure: see text] [Figure: see text] CONCLUSION: The combination of a predisposed low diversity microbiota and baseline inflammation gut may contribute to a more severe outcome for female aged mice infected with C. difficile. [Figure: see text] DISCLOSURES: Vincent B. Young, MD/PhD, ASM: Senior Editor|Debiopharm: Advisor/Consultant|Vedanta Biosciences: Advisor/Consultant