Uncovering the mechanisms of Acinetobacter baumannii virulence

Key Points Acinetobacter baumannii is an opportunistic human pathogen that predominantly causes health-care-associated infections. Many members of the genus Acinetobacter , including Acinetobacter nosocomialis , Acinetobacter pittii , Acinetobacter dijkshoorniae and Acinetobacter seifertii , are also human pathogens and increasingly identified as the cause of infections. A. baumannii is rapidly developing resistance mechanisms to antibiotics. The ability of A. baumannii to withstand desiccation and to form biofilms promotes its success as a nosocomial pathogen. Fundamental virulence factors, such as surface adhesins, glycoconjugates and secretion systems, directly contribute to the pathogenesis of A. baumannii . Recently, virulence mechanisms beyond canonical drug resistance were uncovered that enable Acinetobacter baumannii to thrive in the health-care environment and cause infections in critically ill patients. Harding, Hennon and Feldman explore the molecular features that promote environmental persistence and the most recently identified virulence factors that enable successful human infection. Acinetobacter baumannii is a nosocomial pathogen that causes ventilator-associated as well as bloodstream infections in critically ill patients, and the spread of multidrug-resistant Acinetobacter strains is cause for concern. Much of the success of A. baumannii can be directly attributed to its plastic genome, which rapidly mutates when faced with adversity and stress. However, fundamental virulence mechanisms beyond canonical drug resistance were recently uncovered that enable A. baumannii and, to a limited extent, other medically relevant Acinetobacter species to successfully thrive in the health-care environment. In this Review, we explore the molecular features that promote environmental persistence, including desiccation resistance, biofilm formation and motility, and we discuss the most recently identified virulence factors, such as secretion systems, surface glycoconjugates and micronutrient acquisition systems that collectively enable these pathogens to successfully infect their hosts.