Acinetobacter baumannii: evolution of a global pathogen

Acinetobacter baumannii is an opportunistic nosocomial pathogen and one of the six most important multidrug-resistant microorganisms in hospitals worldwide. This human pathogen is responsible for a vast array of infections, of which ventilator-associated pneumonia and bloodstream infections are the most common, and mortality rates can reach 35%. Community-acquired infections have also been reported, but few strains have been recovered from environmental sources and infection reservoirs external to the hospital have not been identified. The majority of A. baumannii infections are caused by two main population clones with worldwide distribution. Infection outbreaks are often associated with multidrug resistance, including the recent emergence of strains resistant to all available antibiotics. Nevertheless, A. baumannii virulence traits and pathogenic potential have mostly remained elusive. The recent expansion of A. baumannii sequenced genomes has permitted the development of large-array phylogenomic and phenotypic analyses, which can offer valuable insights into the evolution and adaptation of A. baumannii as a human pathogen. This review summarises these recent advances, with particular focus on A. baumannii evolutionary and genomic aspects, and proposes new avenues of research.