OBJECTIVES: This study examines the mechanism of carbapenem resistance in Acinetobacter baumannii isolate Ab244. METHODS: A multiplex PCR for the detection of the bla(OXA-23-like), bla(OXA-40-like), bla(OXA-51-like) and bla(OXA-58-like) families was performed. MICs of imipenem and meropenem were determined by the agar dilution method. The sequence surrounding the bla(OXA-132) gene was determined by amplification with primer pairs encompassing a part of fxsA and an acetyltransferase gene (GNAT). The sequence upstream of the bla(OXA-58) gene was determined by sequencing. SDS-PAGE and carO PCR were performed to check the integrity of the outer membrane proteins. RT-PCRs for the expression of the bla(OXA-132) gene and the bla(OXA-58) gene were performed. RESULTS: Isolate Ab244 harboured bla(OXA-132) belonging to the bla(OXA-51-like) gene cluster and a bla(OXA-58) gene. The 4239 bp region between fxsA and GNAT showed an insert of ISAba16 (where IS stands for insertion sequence) after the first 15 nucleotides of the bla(OXA-132) gene, with an 8 bp target site duplication at the 5' and 3' ends of ISAba16. The sequence oriented in the 5'→3' direction caused insertional inactivation of the bla(OXA-132) gene. The bla(OXA-58) gene was highly expressed by the promoters provided by an ISAba3-like structure found upstream of the gene. The isolate was resistant to meropenem and had intermediate resistance to imipenem, and was also positive for ISAba1. CONCLUSIONS: This is the first report showing ISAba16-mediated inactivation of the bla(OXA-132) gene in strain Ab244. The resistance to carbapenems in strain Ab244 is related to the acquisition of the bla(OXA-58) gene, here governed by an ISAba3-like element.
OBJECTIVES: This study examines the mechanism of carbapenem resistance in Acinetobacter baumannii isolate Ab244. METHODS: A multiplex PCR for the detection of the bla(OXA-23-like), bla(OXA-40-like), bla(OXA-51-like) and bla(OXA-58-like) families was performed. MICs of imipenem and meropenem were determined by the agar dilution method. The sequence surrounding the bla(OXA-132) gene was determined by amplification with primer pairs encompassing a part of fxsA and an acetyltransferase gene (GNAT). The sequence upstream of the bla(OXA-58) gene was determined by sequencing. SDS-PAGE and carO PCR were performed to check the integrity of the outer membrane proteins. RT-PCRs for the expression of the bla(OXA-132) gene and the bla(OXA-58) gene were performed. RESULTS: Isolate Ab244 harboured bla(OXA-132) belonging to the bla(OXA-51-like) gene cluster and a bla(OXA-58) gene. The 4239 bp region between fxsA and GNAT showed an insert of ISAba16 (where IS stands for insertion sequence) after the first 15 nucleotides of the bla(OXA-132) gene, with an 8 bp target site duplication at the 5' and 3' ends of ISAba16. The sequence oriented in the 5'→3' direction caused insertional inactivation of the bla(OXA-132) gene. The bla(OXA-58) gene was highly expressed by the promoters provided by an ISAba3-like structure found upstream of the gene. The isolate was resistant to meropenem and had intermediate resistance to imipenem, and was also positive for ISAba1. CONCLUSIONS: This is the first report showing ISAba16-mediated inactivation of the bla(OXA-132) gene in strain Ab244. The resistance to carbapenems in strain Ab244 is related to the acquisition of the bla(OXA-58) gene, here governed by an ISAba3-like element.
Authors: Hein Trip; Katrin Mende; Joanna A Majchrzykiewicz-Koehorst; Norbert J A Sedee; Albert G Hulst; Hugo-Jan Jansen; Clinton K Murray; Armand Paauw Journal: J Clin Microbiol Date: 2015-03-18 Impact factor: 5.948