Characterization of replication modules in Acinetobacterbaumannii plasmids

MORAN BARRIO J; VIALE AM; SANCHEZ RI

Congreso; Reunion Conjunta 2020 SAIB-SAMIGE; 2020

SAIB-SAMIGE

Acinetobacter baumannii is an important opportunistic pathogen responsible for a variety of nosocomial infections. Its success in the hospital environment results from its ability to evolve multi-drug resistance (MDR) when confronted with antibiotic therapy and in particular, the emerging resistance to last-resort carbapenems (carbR) represents a major concern worldwide. The most frequent cause of carbapenem resistance is represented by acquired Carbapenem-Hydrolyzing class D β-Lactamases (CHDL) of the OXA-23, OXA-40 and OXA-58 groups, with the respective blaOXA genes embedded in genetic structures carried by plasmids. The factors that contribute to antimicrobial resistance in A. baumannii vary considerably between the different clonal complexes that constitute the pathogen population. We have previously characterized clonally and epidemiologically related MDR strains of A. baumannii of the CC15 predominant in our region. One carbR strain, designated Ab242, harbors three plasmids of 25, 12 and 9 kbp designated pAb242_25, pAb242_12, and pAb242_9, respectively. The larger plasmid, pAb242_25,carries an adaptive module containing a ISAba825-blaOXA-58 arrangement and a TnaphA6 transposon granting resistance to carbapenems and aminoglycosides, respectively. Sequence analysis revealed the existence of two modules of replication in pAb242_25, each organized into iterons and AT-rich regions adjacent to a gene encoding replication initiation proteins of the Rep_3 superfamily, designated Rep22 and Rep23, respectively. pAb242_12, in turn, has one replication module also of the iteron type, designated Rep21. Moreover, pAb242_25 can fuse to pAb242_12by means of site-specific recombination mediated by XerC/D sites present in both plasmids, thus generating a co-integrate (pAb342_37) endowed with 3 potentially active replication modules. This cointegrate is the plasmid form successfully rescued after transformation of model Acinetobacter cells and imipenem selection, indicating the requirement of co-integrate formation for the process of lateral transfer of the adaptive module mentioned above.We analyzed here whether the three replication modules carried by pAb242_37 are individually functional in replication, and whether this functionality depends on the transient Acinetobacter host in which these plasmids are located. For this purpose we separately cloned the different Rep modules and tested their functionality in different species of the genus Acinetobacter, such as A. baylyi, A. nosocomialis, and A. baumannii. Our analysis indicated that Rep21, Rep22, and Rep23 are functional in individual form in each of the tested hosts, although the replication efficiency varies depending on the host and the replication module analyzed. The presence of several functional replicons in pAb242_37 could thus expand the plasmid host range when subjected to lateral transfer, thus allowing a more efficient spread of resistance to pathogenic species within the genus.