Intra-molecular inversions of a blaOXA-58 and TnaphA6-containing adaptive module conferring carbapenem- and aminoglycoside-resistance mediated by pairs of pXerC/D sites in Acinetobacter baumannii plasmids

MORAN BARRIO J; VIALE AM; GIACONE L

Córdoba

Congreso; XVIII Congreso Argentino de Microbiología General; 2022

Acinetobacter baumannii is an important opportunistic bacterial pathogen responsible of a variety of infections in healthcare institutions. It can rapidly evolve multi-drug resistance (MDR), and in this context, 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 (CHDL, OXA-type), with the respective blaOXA genes carried by plasmids. We characterized a number of epidemiologically related MDR A. baumannii strains of the clonal complex CC15 predominant in our geographical region. The carbR strains of this collection (Ab242 and Ab825) housed different iteron plasmids, and in both strains, we found a similar plasmid-borne adaptive module containing a blaOXA-58 gene and a TnaphA6 transposon conferring resistance to carbapenems and aminoglycosides, respectively. Notably, these resistance module is bordered by several 28-bp sequences potentially recognized by the XerC and XerD tyrosine recombinases of their hosts (designated pXerC/D-like sites), suggesting functions of this site-specific recombination (SSR) system in their horizontal mobilization. Sequence analysis of the surroundings of the adaptive module indicated an inverted orientation in Ab825 as compared to Ab242. In addition, transformation of sensitive Acinetobacter strains allowed us to identify that some pXerC/D-like sites located in different plasmids from Ab242 could constitute recombinationally active pairs, mediating the fusion as well as the resolution of plasmid co-integrates in this strain (1). Considering that we identified 17 pXerC/D-like sites in Ab242 and Ab825 plasmids, whether some of these sites were active in SSR, and how they 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 Ab242 and Ab825, and the characterization of the plasmids recovered from the carbR transformants using specific primers to detect any pXerC/D hybrid sites by PCR methodologies. We identified that sites 2 and 7 were involved in the reversible intra-molecular inversion of the resistance module and sites 7 and 9 mediated the reversible formation of plasmid co-integrates in both strains. Thus, these results provide first empirical evidences that some of the pXerC/D-like sites present in both Ab242 and Ab825 plasmids could actually conform recombinationally-active pairs. 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, allowing an efficient spread of carbapenem resistance.