Site-specific recombination at XerC/D sites as mediators of plasticity among Acinetobacter baumannii plasmids carrying carbapenem- and aminoglycoside-resistance genetic modules

VIALE, ALEJANDRO M.; REPIZO, GUILLERMO D.; CAMERANESI, MA. MARCELA; MORÁN-BARRIO, JORGELINA; LIMANSKY, ADRIANA S.

Seattle

Congreso; International symposium for plasmid biology 2018; 2018

ISPB

Acinetobacter baumannii is an opportunistic pathogen causing healthcare-associated infections worldwide. A. baumannii clinical strains have demonstrated a remarkable ability to evolve resistance to almost all drugs available (MDR) in the antimicrobial arsenal, including the last-resource carbapenem -lactams mainly from the acquisition of carbapenem-hydrolyzing class-D β-lactamase (CHDL) genes. CHDL genes such as blaOXA-58 are embedded in plasmid-borne genetic structures flanked by short 28-nt motifs potentially recognized by the site-specific XerC and XerD tyrosine-recombinases of the host cell (XerC/D sites). However, whether these sites could mediate site-specific recombination (SSR) events and influence the mobilization of resistance structures was obscure. We recently demonstrated that some of these XerC/D sequences could compose recombinationally-active sister pairs (1). Here we characterized in detail the plasmids carried by A. baumannii Ab825, a MDR clinical strain which displays carbapenem resistance due to overproduction of an acquired blaOXA-58. Plasmids were analyzed by 454 pyrosequencing, comparative sequence analysis, primer walking, and transformation of susceptible Acinetobacter strains. Pyrosequencing indicated the presence of plasmids of 12kb and 36 kbp in Ab825 (pAb825_12 and pAb825_36, respectively), the latter carrying an adaptive module encompassing blaOXA-58 and aphA6 genes flanked by several dif-like sites and conferring simultaneous resistance to carbapenems and aminoglycosides to the host. pAb825_36 was found to represent a co-integrate resulting from a fusion of two plasmids (designated pAb825_27 and pAb825_9, respectively) resulting from a SSR involving XerC/D sites. Evidences were obtained that different pairs of XerC/D sites also mediated inversion events involving the blaOXA-58- and aphA6-containing adaptive module, as well as a fusion between pAb825_27 and pAb825_12. The overall results shed light on the role of XerC/D-mediated SSR in the evolutionary dynamics of A. baumannii plasmids and the underlying mechanisms of dissemination of antimicrobial resistance structures among the Acinetobacter population.