Effect of age on Clostridium difficile infection in a murine model of infection

Abstract

Clostridium difficile, a Gram-positive, spore-forming bacillus, is the leading cause of nosocomial antibiotic-associated diarrhea in the U.S. A major risk factor for developing C. difficile infection (CDI) is advanced age (>65 years), which also accounts for 93% of CDI-related deaths. It is unknown why CDI becomes more severe with age. The objective of this study was to develop a CDI mouse model to study the effects of aging on the pathogenesis of CDI. To achieve this goal we compared CDI in aged (12 months) versus young (2 months) C57BL/6J mice. Six days after C. difficile spore challenge, clinical symptoms (e.g. wet tail, hunching, dehydration) were exhibited by a greater proportion of aged mice compared to young mice (p=0.08). Aged mice experienced greater weight loss than younger animals (p=0.013) and shed greater numbers of bacteria into the feces (p=0.023). Not surprisingly, aged mice suffered a higher cumulative mortality (44%) compared to the young (20%). Histological examination of cecum and colon tissue revealed the severity of inflammation and mucosal damage was greater in aged mice than younger animals (p=0.004). Because mortality is typically associated with lower anti-toxin antibody titers, splenic B cells (CD45+CD19+) numbers were measured by flow cytometry. In comparison to young mice, the proportion of splenic B cells was significantly reduced in the aged group (p=0.006). These results demonstrate that the consequences of CDI are more severe in aged mice and associated with B cell changes. Utilizing our model will help to advance our understanding of age-related changes on host immune defenses against CDI, which is crucial for designing new prophylactic and treatment strategies to reduce morbidity and mortality in older adults.