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

To investigate the mechanism of ceftazidime resistance in two isogenic Acinetobacter baumannii strains from the United Arab Emirates. 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--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. 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 approximate to 200 kb plasmid in strain NM55, while the ceftazidime-susceptible NM128 strain carried an approximate to 180 kb plasmid without the bla(PER-7) gene. Ceftazidime resistance was mediated by a PER-7 -lactamase encoded in an ISCR1 element located on a plasmid. This represents the first detection of a PER-7 -lactamase encoded by a plasmid in A. baumannii.