Plasmid-encoded PER-7 β-lactamase responsible for ceftazidime resistance in Acinetobacter baumannii isolated in the United Arab Emirates

Objectives: To investigate the mechanism of ceftazidime resistance in two isogenic Acinetobacter baumannii strains from the United Arab Emirates. Methods: Two A. baumannii strains, NM55 and NM128, were isolated 4 months apart from a 6-year-old patient in the United Arab Emirates. Genotypic characterization was performed by PFGE and the MIC of ceftazidime was determined by the agar dilution method. Detection of bla _OXA and metallo-β-lactamase genes was performed by multiplex PCR. Analysis of bla _PER-7, ISAba1, bla _ADC and the ISCR1 element was carried out by standard PCR. Plasmid analysis was achieved by Southern blotting. Results: Strain NM55 was resistant to ceftazidime, whereas strain NM128 was susceptible. Both isolates carried the bla _OXA-23 and bla _OXA-64 genes and were identical according to their PFGE patterns. ISAba1 was present upstream of the bla _OXA-23 gene, but absent upstream of bla _ADC-26, in both strains. Strain NM55 possessed a bla _PER-7 gene with the presence of gst, a fragment of the abc transporter and a transposase gene downstream of it. The entire structure was part of an ISCR1 element and was located on an ~200 kb plasmid in strain NM55, while the ceftazidime-susceptible NM128 strain carried an ~180 kb plasmid without the bla _PER-7 gene. Conclusions: Ceftazidime resistance was mediated by a PER-7 β-lactamase encoded in an ISCR1 element located on a plasmid. This represents the first detection of a PER-7 β-lactamase encoded by a plasmid in A. baumannii.