Isolation of Acinetobacter radioresistens from a clinical sample in Bulgaria

We report on the role of Acinetobacter radioresistens in a case of pneumonia in an elderly patient and describe the challenge of correct identification of this species. A tracheobronchial culture taken from a patient in a Bulgarian hospital yielded a pure culture of Gram-negative, lactose-non-fermenting bacilli on MacConkey agar. Genus and species identification was performed by biochemical tests and sequencing of the rpoB gene. Antimicrobial susceptibility testing and screening for blaOXA-like carbapenemase genes was done using microbroth dilution and PCR and sequencing, respectively. The bacillus growing on MacConkey agar was initially identified by biochemical tests as Acinetobacter baumannii complex. Sequencing of the rpoB gene finally identified A. radioresistens. The strain harboured the carbapenemase gene blaOXA-23 without insertion sequences upstream of this gene and was susceptible to imipenem and meropenem. In conclusion, detection of A. radioresistens remains a challenge for routine laboratory diagnostics without performance of molecular identification methods. Although A. radioresistens can be a causative agent of opportunistic infections, in the present case its involvement in the development of pneumonia is doubtful.