Mohammad Hamidian1, Ruth M Hall. 1. School of Molecular Bioscience, The University of Sydney, NSW 2006, Australia.
Abstract
OBJECTIVES: To explore the cause of third-generation cephalosporin resistance in Australian Acinetobacter baumannii isolates belonging to global clone 1 (GC1). METHODS: GC1 isolates from Australia were tested for resistance to ceftazidime and cefotaxime using disc diffusion and MICs. PCR was used to determine the context of ISAba1-ampC configurations and amplicons were sequenced. The level of transcripts was measured using quantitative real-time PCR. Multilocus sequence typing was performed. RESULTS: All ceftazidime- and cefotaxime-resistant isolates carried an appropriately oriented ISAba1 adjacent to the ampC gene and ISAba1 increased ampC transcripts 8-12-fold. In three isolates, the ampC gene next to ISAba1 was not in the normal chromosomal position. Instead, ISAba1 was 7 bp upstream of an additional copy of ampC located in a 3155 bp duplicated segment of the chromosome that differs from the resident GC1 segment by 2.3% but is almost identical to the corresponding region in several non-GC1 draft genomes. The duplicated segment is bounded by directly oriented copies of ISAba1 and flanked by a 9 bp direct duplication. This 5.5 kb transposon, named Tn6168, is in the same position in the chromosome of the three Australian isolates and the GC1 isolate AB0057. Tn6168 was also detected in an unrelated A. baumannii strain, where it was in a different location. The central part of Tn6168 was probably acquired from a sequence type ST32 (Institut Pasteur scheme) A. baumannii strain. CONCLUSIONS: The ISAba1-ampC configuration, which increases ampC expression, can be part of a composite transposon Tn6168.
OBJECTIVES: To explore the cause of third-generation cephalosporin resistance in Australian Acinetobacter baumannii isolates belonging to global clone 1 (GC1). METHODS: GC1 isolates from Australia were tested for resistance to ceftazidime and cefotaxime using disc diffusion and MICs. PCR was used to determine the context of ISAba1-ampC configurations and amplicons were sequenced. The level of transcripts was measured using quantitative real-time PCR. Multilocus sequence typing was performed. RESULTS: All ceftazidime- and cefotaxime-resistant isolates carried an appropriately oriented ISAba1 adjacent to the ampC gene and ISAba1 increased ampC transcripts 8-12-fold. In three isolates, the ampC gene next to ISAba1 was not in the normal chromosomal position. Instead, ISAba1 was 7 bp upstream of an additional copy of ampC located in a 3155 bp duplicated segment of the chromosome that differs from the resident GC1 segment by 2.3% but is almost identical to the corresponding region in several non-GC1 draft genomes. The duplicated segment is bounded by directly oriented copies of ISAba1 and flanked by a 9 bp direct duplication. This 5.5 kb transposon, named Tn6168, is in the same position in the chromosome of the three Australian isolates and the GC1 isolate AB0057. Tn6168 was also detected in an unrelated A. baumannii strain, where it was in a different location. The central part of Tn6168 was probably acquired from a sequence type ST32 (Institut Pasteur scheme) A. baumannii strain. CONCLUSIONS: The ISAba1-ampC configuration, which increases ampC expression, can be part of a composite transposon Tn6168.
Authors: Darren Wong; Travis B Nielsen; Robert A Bonomo; Paul Pantapalangkoor; Brian Luna; Brad Spellberg Journal: Clin Microbiol Rev Date: 2017-01 Impact factor: 26.132
Authors: Mohammad Hamidian; Johanna J Kenyon; Kathryn E Holt; Derek Pickard; Ruth M Hall Journal: J Antimicrob Chemother Date: 2014-06-06 Impact factor: 5.790
Authors: Jane Hawkey; Mohammad Hamidian; Ryan R Wick; David J Edwards; Helen Billman-Jacobe; Ruth M Hall; Kathryn E Holt Journal: BMC Genomics Date: 2015-09-03 Impact factor: 3.969
Authors: Mohammad Hamidian; Matthew Wynn; Kathryn E Holt; Derek Pickard; Gordon Dougan; Ruth M Hall Journal: J Antimicrob Chemother Date: 2013-09-29 Impact factor: 5.790