EVOLUTION OF RESISTANCE PLASMIDS IN Acinetobacter baumannii

CAMERANESI MM; VIALE AM; SANCHEZ RI; MORAN BARRIO J; GIACONE L

Virtual

Congreso; Congreso conjunto SAIB-SAMIGE 2021; 2021

SAIB-SAMIGE

Acinetobacter baumannii is an important opportunistic bacterial pathogen responsible of a variety of infections in healthcare institutions worldwide. It can rapidly evolve multi-drug resistance (MDR), and resistance to last-resort carbapenems (carbR) represents a major concern worldwide. The most frequent cause of carbR in A. baumannii is represented by acquired Carbapenem-Hydrolyzing class D β-Lactamases (OXA β-lactamases), with the respective blaOXA genes carried by plasmids.We previously characterized a number of epidemiologically-related MDR A. baumannii strains of the CC15 clonal complex predominant in our geographical region. The carbR strains of this collection housed different iteron plasmids, some carrying an adaptive module containing a blaOXA-58 gene and a TnaphA6 transposon conferring resistance to carbapenems and aminoglycosides, respectively. Similar blaOXA-58-containing modules are widely found among A. baumannii plasmids, although the genetic contexts in which they are embedded vary considerably between plasmids. Notably, these and other resistance modules are bordered by several 28-bp sequences potentially recognized by the XerC/D tyrosine recombinases of their hosts (designated pXerC/D-like sites), suggesting functions of this site recombination system (SSR) in their horizontal mobilization. Yet, whether at least some of these pXerC/D-like sites were active in SSR, and how they could mediate mobilization of the modules they encompass, is only beginning to be understood. To address these questions, we used a combination of methodologies that included transformation of susceptible Acinetobacter strains with total plasmids obtained from local carbR A. baumannii strains, the characterization of the plasmids selected in these transformants, the cloning and sequencing of plasmid fragments, and the final verification of any detected pXerC/D hybrid sites by PCR methodologies. This allowed us to provide first empirical evidences that some of the above mentioned pXerC/D-like sites could actually conform recombinationally-active pairs promoting the reversible formation of plasmid co-integrates as well as the intra-molecular inversion of the structures they encompass in the plasmid molecule. Notably, all of the experimentally-detected active pXerC/D sites share at their core regions identical 6-bp central regions separating the corresponding XerC- and XerD-binding motifs. This dynamic state of plasmid architectures resulting from both intra- and inter-molecular recombination mediated by different pXerC/D active pairs supports our previous proposals (1) of their contribution to the evolution of Acinetobacter plasmids. These observations, added to the presence of different functional replicons in a single A. baumannii cell showed previously, certainly expands the host range in the event of lateral transfer, allowing an efficient spread of carbapenem resistance.1. Cameranesi et al. (2018) Front Microbiol. 9:66. doi: 10.3389/fmicb.2018.00066.