Delayed identification of Acinetobacter baumannii during an outbreak owing to disrupted blaOXA-51-like by ISAba19

- blaOXA-51-like is a molecular detection marker for Acinetobacter baumannii.
- blaOXA-51-like was not amplified in 14 A. baumannii outbreak isolates.
- ISAba19 disrupted blaOXA-51-like and the amplified PCR band was 1.7 kb instead of 353 bp.
- Besides blaOXA-51-like, gyrB or rpoB multiplex PCR may be reliable for rapid detection of A. baumannii.

Early detection of Acinetobacter baumannii, an emerging pathogen in hospital settings, is of interest. The blaOXA-51-like family had been used as a marker to detect A. baumannii. During an infection outbreak, 14 isolates produced a 1.7-kb PCR band instead of 353 bp for this marker. This work sought the reasons behind the increased marker size. Characterisation of isolates was done by API-20NE, gyrB multiplex PCR and 16S-23S rRNA ITS sequencing. The 1.7-kb band generated and the complete blaOXA-51-like variant were sequenced to find the probable integrated element. Susceptibility testing to various antimicrobials was performed by microdilution. blaOXA-like, metallo-β-lactamases (MBLs), the ISAba1 element and the presence of ISAba1 adjacent to blaOXA-like were sought. rep-PCR, global clonal (GC) lineage determination and multilocus sequence typing (MLST) were performed to analyse the relationship among isolates. Isolates were characterised as Acinetobacter baumannii-calcoaceticus complex by API-20NE. gyrB multiplex PCR and 16S-23S ITS sequencing verified the isolates as A. baumannii. Sequencing of the 1.7-kb band revealed ISAba19 as the disrupting element. The blaOXA-51 variant was blaOXA-66, which was elongated to 2.2 kb due to ISAba19. The blaOXA-23-like family was found in 67% of isolates. MBL genes were not detected; however, ISAba1-blaOXA-23-like was characterised in carbapenem-resistant isolates (53%; 8/15). Isolates were divided into three clusters by rep-PCR. All strains were ST2 and all but one belonged to GC II. Identification of A. baumannii based only on blaOXA-51-like is not reliable. Besides blaOXA-51-like, multiplex PCR of gyrB and rpoB could provide rapid and cost-effective results.