Interplay of horizontal gene transfer, carO allele exchange, and ISAba825-induced blaOXA-58 overexpression in the evolution of carbapenem resistance among Acinetobacter baumannii strains in Rosario, Argentina

PIAZZA, A; LIMANSKY, A; MUSSI, M.A.; JORGELINA MORÁN BARRIO; BRAMBILLA, L; VIALE, A.M.

Colonia

Simposio; 9th International Symposium on the Biology of Acinetobacter.; 2013

Objectives: We previously described a new family of outer membrane (OM) proteins, CarO, whose gene inactivation or exchange mediated by horizontal gene transfer (HGT) is associated to increased carbapenem resistance in Acinetobacter baumannii. We also reported two novel IS, ISAba825 and ISAba125, disrupting carO among carbapenem-resistant A. baumannii clinical strains, and that a hybrid promoter generated by ISAba825 insertion strongly increased blaOXA-58 expression resulting in carbapenem resistance. We evaluate here the interplay of genetic events associated to carbapenem resistance evolution among epidemiologically-related A. baumannii strains in a public hospital of Rosario, Argentina. Methods: Clonal relatedness among isolates was determined by MLST, PFGE, and PCR fingerprinting. The multidrug-resistant epidemiologically related strains analysed included a carbapenem sensitive (Ab244) and two carbapenem resistant (Ab242 and Ab825) strains. Presence of blaOXA58, ISAba825, ISAba825-blaOXA-58 arrangements, and carO variant allele were evaluated by specific PCR and sequencing. OM protein profiles were analysed by SDS-PAGE. Results: Ab244, Ab242, and Ab825 exhibited the same MLST (ST104) and were genetically related as judged by PFGE and PCR fingerprinting. Neither ISAba825 nor blaOXA-58 could be identified in Ab244, which harbours carO II. Conversely, plasmid-borne ISAba825-blaOXA-58 arrangements were detected in Ab242 and Ab825. Ab242 harbors carO III, and Ab825 a ISAba825-interrupted carO III allele promoting loss of CarO from the OM. Conclusion: A series of events involving both HGT- and IS-derived events are proposed to account for the evolution of carbapenem resistant phenotypes. Ab242 probably aroused from HGT-derived recombination events that occurred in a recipient strain clonally related to Ab244, such as the exchange of carO alleles and the acquisition of a plasmid-borne ISAba825-blaOXA-58 arrangement followed by selection under carbapenem therapy pressure. Yet, the identification of strain Ab825 further containing an ISAba825-disrupted carO III allele suggests that the total loss of CarO promoted additional increments of fitness, and supports relevant roles for CarO family members in carbapenem permeation across the A. baumannii OM.