Characterization of the Diversity in Host Range of an Extensively Drug-Resistant (XDR) Type IV Secretion System-Encoding Plasmid in Acinetobacter

The World Health Organization (WHO) cites antimicrobial resistance as among the greatest threats to human health. The multidrug-resistant pathogen <i>Acinetobacter baumannii</i>, recognized as a priority pathogen for healthcare and research, is responsible for a diverse array of infections including respiratory tract, soft tissue and wound, and bloodstream infections. Despite this importance, the mechanisms of its pathogenesis remain poorly understood. Conjugation represents a central mechanism for bacterial adaptation and evolution and is responsible for the spread of genes that promote pathogen survival, antibiotic resistance, virulence, and biofilm formation. Our laboratory recently characterized a large group of almost 120 Type IV Secretion System (T4SS)-encoding plasmids in <i>Acinetobacter</i>, distributed globally across 20 countries spanning four continents, and demonstrated that an XDR <i>A. baumannii</i> plasmid from this family was transmissible to another <i>A. baumannii</i> strain. This research investigated the potential diversity of host strains for this representative member plasmid. Using the GC1 lineage strain <i>A. baumannii</i> AB5075-UW harbouring the XDR plasmid p1AB5075 and a series of previously characterized clinical and environmental <i>Acinetobacter</i> strains, conjugative analyses demonstrated transfer of the XDR plasmid to both <i>A. baumannii</i> strains of more genetically divergent sequence types and to non-<i>baumannii Acinetobacter</i> species both inside and outside the <i>Acinetobacter calcoaceticus-baumannii</i> (ACB) complex. Successful recipients included diverse strains of both clinical and environmental origin within the <i>Acinetobacter</i> genus. Collectively, this research could provide insights into an important genetic element for future surveillance.