Uncommon carbapenemase-encoding plasmids in the clinically emergent Acinetobacter pittii

Objectives: Two carbapenemase-carrying plasmids, pLS488 (bla(OXA-23)) and pLS535 (bla(OXA-58)) from Acinetobacter pittii clinical isolates, were characterized in this study, including their ability to be transferred to Acinetobacter baumannii. Methods: The clinical isolates were obtained from drainage fluid of a patient with biliary tract cancer and from an exudate of a patient with a hip infection (Portuguese University Hospital, 2012). Isolate characterization included antimicrobial susceptibility tests, carbapenemase production by Blue-Carba, carbapenem-hydrolysing class D beta-lactamase (CHDL) gene search by PCR sequencing, ApaI-PFGE, CHDL genetic location and plasmid size by hybridization and WGS. Plasmid transfer was performed by conjugation or electroporation. Results: pLS488 constitutes the first conjugative plasmid reported to carry a carbapenem resistance gene in A. pittii and is part of a potential new incompatibility group that might also account for the dissemination of OXA-23 in A. baumannii. pLS535 belongs to the Acinetobacter GR7 incompatibility group and presents a new scaffold for OXA-58. This plasmid lacked the machinery for conjugation, but was transferable by electroporation to A. baumannii. Both isolates, which displayed the same PFGE pattern, represent the first report of CHDL-carrying A. pittii in Portuguese hospitals. Conclusions: Altogether, these results emphasize the importance of A. pittii, or particular A. pittii clones, as a source of resistance genes, facilitating their dissemination among different bacterial species.