April 21, 2020  |  

Clinical and laboratory-induced colistin-resistance mechanisms in Acinetobacter baumannii.

Authors: Boinett, Christine J and Cain, Amy K and Hawkey, Jane and Do Hoang, Nhu Tran and Khanh, Nhu Nguyen Thi and Thanh, Duy Pham and Dordel, Janina and Campbell, James I and Lan, Nguyen Phu Huong and Mayho, Matthew and Langridge, Gemma C and Hadfield, James and Chau, Nguyen Van Vinh and Thwaites, Guy E and Parkhill, Julian and Thomson, Nicholas R and Holt, Kathryn E and Baker, Stephen

The increasing incidence and emergence of multi-drug resistant (MDR) Acinetobacter baumannii has become a major global health concern. Colistin is a historic antimicrobial that has become commonly used as a treatment for MDR A. baumannii infections. The increase in colistin usage has been mirrored by an increase in colistin resistance. We aimed to identify the mechanisms associated with colistin resistance in A. baumannii using multiple high-throughput-sequencing technologies, including transposon-directed insertion site sequencing (TraDIS), RNA sequencing (RNAseq) and whole-genome sequencing (WGS) to investigate the genotypic changes of colistin resistance in A. baumannii. Using TraDIS, we found that genes involved in drug efflux (adeIJK), and phospholipid (mlaC, mlaF and mlaD) and lipooligosaccharide synthesis (lpxC and lpsO) were required for survival in sub-inhibitory concentrations of colistin. Transcriptomic (RNAseq) analysis revealed that expression of genes encoding efflux proteins (adeI, adeC, emrB, mexB and macAB) was enhanced in in vitro generated colistin-resistant strains. WGS of these organisms identified disruptions in genes involved in lipid A (lpxC) and phospholipid synthesis (mlaA), and in the baeS/R two-component system (TCS). We additionally found that mutations in the pmrB TCS genes were the primary colistin-resistance-associated mechanisms in three Vietnamese clinical colistin-resistant A. baumannii strains. Our results outline the entire range of mechanisms employed in A. baumannii for resistance against colistin, including drug extrusion and the loss of lipid A moieties by gene disruption or modification.

Journal: Microbial genomics
DOI: 10.1099/mgen.0.000246
Year: 2019

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