Detection of active pairs of XerC/D recognition sites mediating fusions and inversions in Acinetobacter baumannii plasmids carrying OXA-58 carbapenemase adaptive modules

LIMANSKY AS; MORAN BARRIO J; VIALE AM; CAMERANESI MM; REPIZO GD

Frankfurt

Simposio; Acinetobacter 2019; 2019

Acquired carbapenem-hydrolysing class-D β-lactamases (OXA-type) represent main factors ofcarbapenem resistance among multi-drug resistant (MDR) Acinetobacter baumannii (Aba) strains.Similarly to other OXA carbapenemases, OXA-58 genes (bla OXA-58 ) are embedded in plasmid-bornegenetic structures which are flanked by a variable number of short 28-nucleotide motifs potentiallyrecognized by the XerC/XerD site-specific recombination system (SSR) of the bacterial hosts (pXerC/Dor pdif sites) [1]. It is poorly understood, however, how pXerC/D sites mediate mobilisation of the adaptivemodules linked to them. We have recently demonstrated in Aba strains assigned to CC15 (Pasteurscheme) the existence of an active pair of pXerC/D sites promoting cointegrate formation betweenplasmids containing a bla OXA-58 - and TnaphA6-resistance structure [1]. Here, we report the presence ofadditional pairs of pXerC/D sites mediating not only plasmid fusions and resolutions, but also the intra-molecular inversion of the adaptive module.The sequences of Ab825 plasmids were determined by 454 pyrosequencing and plasmid walking. A 28-nucleotide XerC/D consensus sequence was inferred from a local database of 215 Aba plasmidsdeposited in databases, and used to search potential sites in Ab825 plasmids. Cointegrate formation wasdetected by transformation of susceptible Acinetobacter strains, and the identification of sister pXerC/Dpairs active in SSR by PCR and amplicon sequencing.Aba plasmids of less than 50 kbp were found to contain an average of 3-5 pXerC/D-like sites permolecule, larger plasmids were mostly devoid of these sites. Sequence analysis revealed the presenceof three plasmids in Ab825: pAb825_27 (27 kbp), pAb825_12 (12 kbp), and pAb825_9 (9 kbp), eachbearing several pXerC/D sites. A co-integrate (pAb825_36) was also detected resulting from the fusionof pAb825_27 and pAb825_9 mediated by an active pair of pXerC/D sites. Two additional active pairswere uncovered, one mediating the intra-molecular inversion of the bla OXA-58 - and TnaphA6-containingstructure and the other the fusion between pAb825_27 and pAb825_12. These observations shed lighton the role of pXerC/D-mediated SSR in the evolutionary dynamics of Aba plasmids and the underlyingmechanisms of dissemination of antimicrobial resistance and other adaptive structures among theAcinetobacter population.