Gene dependence during mammalian Acinetobacter baumannii pneumonia and septicaemia infections

Abstract

With a limited number of traditional virulence factors, the success of the nosocomial pathogen Acinetobacter baumannii is largely attributed to its ability to persist and resist. The niches encountered during infection vary significantly from the more commonly studied laboratory setting, and consequently, the genes responsible for in vivo pathogenesis have yet to be fully elucidated. This study utilized the A. baumannii AB5075-UW transposon mutant library with unbiased genome-wide transposon sequencing to identify the genetic basis for survival and fitness during pneumonia and septicaemia infections. We identified 128 genes essential for in-host survival, including 22 required for survival in all tissues. Additionally, 302 genes with significantly altered fitness in vivo were also identified. Tissue specificity was observed, highlighting the importance of genes associated with aa biosynthesis in the lungs, cell shape and structure in the kidneys and metal acquisition during septicaemia. The majority (89%) of the genes with aberrant fitness were constituents of the core A. baumannii genome. The findings were validated using a subset of targeted mutants, including those required for infection (phoB, cysI and hom) or specifically septicaemia (corA, lepA and purN) or pneumonia (argC, hisC and leuD), confirming that these observations were a result of specific in vivo fitness defects rather than aberrant in vitro growth. Taken together, these data provide the first global profile of genes required for in vivo fitness of A. baumannii during different disease states and growth in different tissues. Impact Statement Acinetobacter baumannii is an important human pathogen responsible for a range of life-threatening infections. The rapid global emergence of multi-, extensively-and pandrug-resistant strains has seen morbidity and mortality rates rise, with untreatable infections now a reality. To address the current void of new therapeutics in development, a more complete understanding of A. baumannii in vivo survival is required. Here, we used unbiased genome-wide transposon insertion sequencing to identify genes required for survival and bacterial fitness in vivo and examined tissue and infection route specificity. We identified 128 and 302 genes that are essential for survival and influence in vivo fitness, respectively, and confirmed that 89% of these were part of the A. baumannii core genome, suggesting that these are species-wide virulence determinants. Advancing our understanding of this important human pathogen and the mechanisms responsible for disease will greatly assist in the development of new therapeutic or preventative approaches.