Recombination among plasmid-borne genetic platforms containing blaOXA-58 genes in the pan-dissemination of carbapenem resistance in Acinetobacter spp.

CAMERANESI, M; MORAN-BARRIO, J.; LIMANSKY, A; VIALE, A

Congreso; XI Congreso Argentino de Microbiología General; 2015

Over-production of carbapenem-hydrolyzing class D β-lactamases (CHDLs) is the most frequent cause of carbapenem resistance among multi-drug resistant (MDR) ACB complex members such as the Acinetobacter baumannii, A. pittii and A. nosocomialis which account for the majority of Acinetobacter infections (1). Short genomic sequences designated Re27 sequences are implicated in site specific recombination processes involved in the evolution of many plasmids (2). These sequences have been associated with particular replicase genes and could constitute favored insertion sites for structures carrying CHDL genes (3). We characterized here a non-conjugative plasmid (pAb242) from a carbapenem- and aminoglycoside-resistant MDR A. baumannii strain carrying a genetic platform containing blaOXA-58 and aphA6 genes, and searched for the presence of Re27-like sites in this structure. We also conducted a comparative analysis with similar platforms present in previously reported plasmids from other Acinetobacter spp. The pAb242 platform encompasses ~9 kbp and is bracketed by two Re27-like recombination sites, and is contiguous to a resolvase gene of the serine-recombinase family thus containing all necessary resources for intra-genomic mobilization. blaOXA-58 is embedded in this platform into an imperfect composite Tn3-like transposon in which the upstream 5´-ISAba3 was targeted by an ISAba825 element. araC1 and lysE regulatory genes were found downstream of the second ISAba3 of the Tn3 element, being lysE disrupted by TnaphA6. MAUVE comparisons with other nine platforms from Acinetobacter plasmids showed in all cases a similar arrangement containing blaOXA-58, araC1 and lysE genes. On the contrary, distinctive features were found between similar platforms such as different ISs disrupting the 5´-ISAba3 element at different positions, and different insertions sites for TnaphA6 into lysE. Re27-like recombination sites were identified bordering the corresponding platforms in seven of the above arrangements. These Re27-like sequences allow the occurrence of multiple recombination processes, thus promoting different arrangements of blaOXA-58 containing regions such as inversion mechanisms and plasmid concatenate formation. These platforms were identified in different context, i.e. 30-100 kbp plasmids, some of them containing more than one rep gene. We propose that Re27-mediated recombination processes of platforms containing resistance genes such as those described above account for the evolution of plasmids responsible of pan-dissemination of carbapenem resistance among the Acinetobacter population.