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 Acinetobacter baumannii, 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 Acinetobacter, distributed globally across 20 countries spanning four continents, and demonstrated that an XDR A. baumannii plasmid from this family was transmissible to another A. baumannii strain. This research investigated the potential diversity of host strains for this representative member plasmid. Using the GC1 lineage strain A. baumannii AB5075-UW harbouring the XDR plasmid p1AB5075 and a series of previously characterized clinical and environmental Acinetobacter strains, conjugative analyses demonstrated transfer of the XDR plasmid to both A. baumannii strains of more genetically divergent sequence types and to non-baumannii Acinetobacter species both inside and outside the Acinetobacter calcoaceticus-baumannii (ACB) complex. Successful recipients included diverse strains of both clinical and environmental origin within the Acinetobacter genus. Collectively, this research could provide insights into an important genetic element for future surveillance.