Aging exacerbates mortality of Acinetobacter baumannii pneumonia and reduces the efficacies of antibiotics and vaccine

Abstract

Pneumonia caused by <i>Acinetobacter baumannii</i> has become a serious threat to the elderly. However, there are no experimental studies on the relevance between aging and <i>A. baumannii</i> infections. Here, we established an aged pneumonia mouse model by non-invasive intratracheal inoculation with <i>A. baumannii</i>. Higher mortality was observed in aged mice along with increased bacterial burdens and more severe lung injury. Increased inflammatory cell infiltration and enhanced pro-inflammatory cytokines at 24 hours post infection were detected in aged mice than those in young mice. Moreover, infected aged mice had lower myeloperoxidase levels in lungs and less reactive oxygen species-positive neutrophils in bronchoalveolar lavage fluid compared with infected young mice. Reduced efficacy of imipenem/cilastatin against <i>A. baumannii</i> was detected in aged mice. Vaccination of formalin-fixed <i>A. baumannii</i> provided 100% protection in young mice, whereas the efficacy of vaccine was completely diminished in aged mice. In conclusion, aging increased susceptibility to <i>A. baumannii</i> infection and impaired efficacies of antibiotics and vaccine. The aged mice model of <i>A. baumannii</i> pneumonia is a suitable model to study the effects of aging on <i>A. baumannii</i> infection and assess the efficacies of antibiotics and vaccines against <i>A. baumannii</i> for the elderly.