Analysis of <i>Acinetobacter</i> P-type type IV secretion system-encoding plasmid diversity uncovers extensive secretion system conservation and diverse antibiotic resistance determinants

<i>Acinetobacter baumannii</i> is globally recognized as a multi-drug-resistant pathogen of critical concern due to its capacity for horizontal gene transfer and resistance to antibiotics. Phylogenetically diverse <i>Acinetobacter</i> species mediate human infection, including many considered as important emerging pathogens. While globally recognized as a pathogen of concern, pathogenesis mechanisms are poorly understood. P-type type IV secretion systems (T4SSs) represent important drivers of pathogen evolution, responsible for horizontal gene transfer and secretion of proteins that mediate host-pathogen interactions, contributing to pathogen survival, antibiotic resistance, virulence, and biofilm formation. Genes encoding a P-type T4SS were previously identified on plasmids harboring the carbapenemase gene <i>bla_NDM-1</i> in several clinically problematic <i>Acinetobacter</i>; however, their prevalence among the genus, geographical distribution, the conservation of T4SS proteins, and full capacity for resistance genes remain unclear. Using systematic analyses, we show that these plasmids belong to a group of 53 P-type T4SS-encoding plasmids in 20 established <i>Acinetobacter</i> species, the majority of clinical relevance, including diverse <i>A. baumannii</i> sequence types and one strain of <i>Providencia rettgeri</i>. The strains were globally distributed in 14 countries spanning five continents, and the conjugative operon's T4SS proteins were highly conserved in most plasmids. A high proportion of plasmids harbored resistance genes, with 17 different genes spanning seven drug classes. Collectively, this demonstrates that P-type T4SS-encoding plasmids are more widespread among the <i>Acinetobacter</i> genus than previously anticipated, including strains of both clinical and environmental importance. This research provides insight into the spread of resistance genes among <i>Acinetobacter</i> and highlights a group of plasmids of importance for future surveillance.