Gene dependence during mammalian Acinetobacter baumannii pneumonia and septicaemia infections

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.