Towards an explanation for the success of Acinetobacter baumannii in the human host

Abstract

Acinetobacter baumannii is an important nosocomial pathogen responsible for outbreaks of infection worldwide. The studies presented in this thesis aimed to gain further insight into the bacterial and host factors associated with the pathogenesis of A. baumannii to seek an explanation for the clinical success of A. baumannii. We demonstrated that both A. baumannii and less virulent Acinetobacter species can adhere to surfaces and form a biofilm, albeit with a wide variation among strains of each species. These results first of all show that a single strain is not representative for the species. Secondly, the presence of many virulence attributes in both clinically relevant and less-relevant strains indicates that the clinical success of A. baumannii cannot be explained by these virulence factors alone. Moreover, our results suggest that the outcome of infection depends mainly on the host. In this respect, a specific host innate immune response induced by different A. baumannii strains was associated with the outcome of A. baumannii pneumonia. Thus, the ability of certain A. baumannii strains to induce specific immune responses in susceptible hosts in combination with their metabolic versatility and a MDR phenotype are likely to be important features associated with the clinical success of this pathogen.