Xer site-specific recombination and IS26 mediated plasmid rearrangements in Acinetobacter baumannii: implications for resistance gene acquisition and evolution.

GIACONE L; VIALE AM; MORAN BARRIO J

Rosario

Congreso; LIX Congreso SAIB; 2023

SAIB

Acinetobacter baumannii (Ab) represents a major cause of healthcare-associated infections, generally affecting immune-compromised and severely injured patients; with the global spread of a number of epidemic clonal complexes (CC) displaying multidrug-resistance (MDR) phenotypes including last-resort carbapenems (carbR). The most frequent cause of carbR in Ab relies on acquired OXA-type carbapenemases, with the respective blaOXA genes carried by plasmids. Thus, a detailed characterization of MDR Ab plasmids is essential for understanding the evolution and dissemination of these resistance structures.We characterized a number of epidemiologically related MDR Ab strains belonging to the CC15 prevalent in our geographical region. The carbR strains (Ab242 and Ab825) housed different iteron plasmids carrying a blaOXA-58 and TnaphA6-containing resistance module (RM) conferring resistance to carbapenems and aminoglycosides, respectively. Notably, this RM is bordered by several 28-bp sequences potentially recognized by the XerC and XerD tyrosine recombinases of their hosts (pXerC/D-like sites), suggesting functions of this site-specific recombination (SSR) system in their horizontal mobilization. In Ab825, the RM is present in a 27 kbp plasmid-domain (pAb825_27) forming a larger 36-kbp tri-replicon plasmid (pAb825_36), which contains an additional 9-kbp plasmid-domain (pAb825_9). Interestingly, a similar sequence to pAb825_9 was found in a 7 kbp plasmid from the carbS strain Ab244 (pAb244_7), isolated two years earlier than the carbR strains1,2. Here we propose an evolutionary path for the genesis of plasmids present in these MDR Ab strains, involving Xer-dependent SSR and IS26-mediated mechanisms.By conducting BlastN searches against GenBank database, using the Ab825 plasmids as queries, we identified a series of plasmids carried by CC15 Ab strains isolated in Argentina and Chile. These plasmids, including pAb244_7, share backbones similar to pAb825_9, containing repAci4 and mobA/mobL modules2,3. We found in pAb825_9 an additional DNA region containing genes for a toxin-antitoxin system and a ferredoxin, bordered by directly oriented pXerC/D sites (C14/D14 and C16/D16). The identification of a hybrid C14/D16 site in pAb244_7 suggests that a Xer-mediated event contributed to the acquisition of this stability module in Ab825. In addition, we observed an IS26 insertion in pAb244_7, similar to a composite transposon in a Chilean plasmid carrying blaTEM and aacC2 resistance genes. Our results underscore the pivotal role of Xer-SSR and IS26-mediated events in plasmid evolution within MDR Ab strains, further aiding in the dissemination of resistance genes and the rapid adaptation of the bacterial host in dynamic environments.1) Giacone et al. 2023 Front Microbiol. 9(14) doi:10.3389/fmicb.2023.10576082) Cameranesi et al. 2020 Microb Genom 6(9). doi:10.1099/mgen.0.0003603) Brito et al. 2022 Microbiol Spectr.10 (5). doi:10.1128/spectrum.02463-22