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

Early detection of Acinetobacter baumannii, an emerging pathogen in hospital settings, is of interest. The bla_OXA-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 bla_OXA-51-like variant were sequenced to find the probable integrated element. Susceptibility testing to various antimicrobials was performed by microdilution. bla_OXA-like, metallo-β-lactamases (MBLs), the ISAba1 element and the presence of ISAba1 adjacent to bla_OXA-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 bla_OXA-51 variant was bla_OXA-66, which was elongated to 2.2 kb due to ISAba19. The bla_OXA-23-like family was found in 67% of isolates. MBL genes were not detected; however, ISAba1-bla_OXA-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 bla_OXA-51-like is not reliable. Besides bla_OXA-51-like, multiplex PCR of gyrB and rpoB could provide rapid and cost-effective results.