GR13-type plasmids in potentiate the accumulation and horizontal transfer of diverse accessory genes.

Carbapenem and other antibiotic resistance genes (ARGs) can be found in plasmids in , but many plasmid types in this genus have not been well-characterized. Here we describe the distribution, diversity and evolutionary capacity of group 13 (GR13) plasmids that are found in species from diverse environments. Our investigation was prompted by the discovery of two GR13 plasmids in isolated in an intensive care unit (ICU). The plasmids harbour distinct accessory genes: pDETAB5 contains and genes that confer resistance to four further antibiotic classes, while pDETAB13 carries putative alcohol tolerance determinants. Both plasmids contain multiple modules, which are flanked by p sites recognized by XerC/XerD tyrosine recombinases. The ARG-containing modules in pDETAB5 are almost identical to those found in pDETAB2, a GR34 plasmid from an unrelated isolated in the same ICU a month prior. Examination of a further 41 complete, publicly available plasmid sequences revealed that the GR13 pangenome consists of just four core but 1186 accessory genes, 123 in the shell and 1063 in the cloud, reflecting substantial capacity for diversification. The GR13 core genome includes genes for replication and partitioning, and for a putative tyrosine recombinase. Accessory segments encode proteins with diverse putative functions, including for metabolism, antibiotic/heavy metal/alcohol tolerance, restriction-modification, an anti-phage system and multiple toxin–antitoxin systems. The movement of modules and actions of insertion sequences play an important role in generating diversity in GR13 plasmids. Discrete GR13 plasmid lineages are internationally disseminated and found in multiple species, which suggests they are important platforms for the accumulation, horizontal transmission and persistence of accessory genes in this genus.