History of the taxonomy of Acinetobacter: the emergence of hospital-adapted species of global health concern

The genus <i>Acinetobacter</i> is widely distributed in nature. A key step in the evolutionary trajectory of <i>Acinetobacter</i> is the diversification of species that are well adapted to human-made environments, particularly hospitals, including those capable of causing infection outbreaks. The temporal dynamics, routes and mechanisms of such nosocomial adaptations remain to be elucidated. This review provides a comprehensive description of 162 <i>Acinetobacter</i> isolates collected between 1910 and 1970 under various taxonomic names, which may facilitate a more detailed exploration of the pathogenic and nosocomial shifts of <i>Acinetobacter</i>. Genomic analysis of these isolates can help reveal the earliest traits of antimicrobial resistance and detect initial genetic events, thereby allowing hypotheses on driving factors that may have preceded the extensive use of modern antimicrobials. Through comparison with contemporary isolates, the evolutionary events and ecological processes that have shaped the phylogeny of today's highly successful <i>Acinetobacter</i> strains can be mapped, and their arsenals of antimicrobial resistance determinants and virulence factors can be tracked chronologically.