Centre for Infectious Diseases, The University of Edinburgh, 49 Little France Crescent, Edinburgh EH16 4SB, UK.
J Antimicrob Chemother. 2012 Jan;67(1):59-63. doi: 10.1093/jac/dkr415. Epub 2011 Oct 5.
This study examines the mechanism of carbapenem resistance in Acinetobacter baumannii isolate Ab244.
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.
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.
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.
本研究旨在探讨鲍曼不动杆菌 Ab244 株碳青霉烯类耐药的机制。
采用多重 PCR 法检测 bla(OXA-23 样）、bla(OXA-40 样）、bla(OXA-51 样）和 bla(OXA-58 样）家族。采用琼脂稀释法测定亚胺培南和美罗培南的 MIC。用引物对扩增包括部分 fxsA 和乙酰转移酶基因（GNAT）的 bla(OXA-132)基因周围序列。通过测序确定 bla(OXA-58)基因上游序列。进行 SDS-PAGE 和 carO PCR 以检查外膜蛋白的完整性。进行 bla(OXA-132)基因和 bla(OXA-58)基因的 RT-PCR。
Ab244 株携带 bla(OXA-132），属于 bla(OXA-51 样）基因簇和 bla(OXA-58)基因。bla(OXA-132)基因的前 15 个核苷酸之后，fxsA 和 GNAT 之间的 4239 bp 区域插入了 ISAba16（其中 IS 代表插入序列），在 ISAba16 的 5'和 3'端有 8 bp 靶序列重复。从 5'→3'方向的序列导致 bla(OXA-132)基因的插入失活。bla(OXA-58)基因由位于基因上游的 ISAba3 样结构提供的启动子高度表达。该分离株对美罗培南耐药，对亚胺培南中介耐药，且 ISAba1 阳性。
这是首次报道 ISAba16 介导的 bla(OXA-132)基因在 Ab244 株中的失活。Ab244 株对碳青霉烯类的耐药性与 bla(OXA-58)基因的获得有关，该基因由 ISAba3 样元件调控。
