Acinetobacter radioresistens as a silent source of carbapenem resistance for Acinetobacter spp.

Carbapenem resistance results mostly from the expression of acquired carbapenem-hydrolyzing oxacillinases in Acinetobacter baumannii. The bla(OXA-23) oxacillinase gene is increasingly reported worldwide and may represent an emerging threat. Our goal was to identify the progenitor of that carbapenemase gene. A collection of 50 Acinetobacter sp. strains corresponding to several Acinetobacter species was screened for bla(OXA-23)-Iike genes by PCR and hybridization techniques. Five Acinetobacter radioresistens isolates that were susceptible to carbapenems harbored chromosomally encoded bla(OXA-23)-Iike genes. A similar plasmid backbone was identified in several bla(OXA-23)-positive A. baumannii and A. radioresistens isolates, further strengthening the vectors of exchanges for these bla(OXA-23)-like genes. Therefore, A. radioresistens, a commensal bacterial species which is identified on the skin of hospitalized and healthy patients (a property shared with A. baumannii), was identified as the source of the bla(OXA-23) gene.