Differential impact of ramRA mutations on both ramA transcription and decreased antimicrobial susceptibility in Salmonella Typhimurium
Differential impact of ramRA mutations on both ramA transcription and decreased antimicrobial susceptibility in Salmonella Typhimurium
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DOI：
10.1093/jac/dkv410
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发表时间：
2016-03-01
影响因子：
5.2
通讯作者：
Vila, Jordi
中科院分区：
文献类型：
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作者：
Fabrega, Anna;Balleste-Delpierre, Clara;Vila, Jordi
本研究旨在分析鼠伤寒沙门氏菌外排介导的多药耐药调控因子突变的异质性。此外，还评估了这些突变对RAMA、AcrB、TolC和ACRF转录的影响，以及对耐药或敏感性降低表型的影响。用Etest和肉汤微量稀释法测定了几种无关化合物的最低抑菌浓度。对喹诺酮类药物靶基因和多药耐药调节剂的突变进行筛查。RT-PCR检测AcrB、TolC、OmpF、ACRF、EMRB、acrR、RAMA、SOXS和marA的表达水平。除卡那霉素外，所有突变株的MIC值均升高。并不是所有的突变体都存在喹诺酮类药物靶基因的突变，这些突变体都在ramRA调节区存在突变。所有突变株都高表达RAMA、TolC和AcrB(仅在60wt的衍生物中测试)，而其余基因的结果不同。与耐药性和/或对抗生素敏感性降低有关的ramRA区突变在沙门氏菌中占主导地位。突变类型存在异质性，影响RamR结合位点的缺失对RAMA的表达和MDR表型有更大的影响。
This study was focused on analysing the heterogeneity of mutations occurring in the regulators of efflux-mediated MDR in Salmonella Typhimurium. Moreover, the impact of such mutations on impairing the transcription of ramA, acrB, tolC and acrF was also assessed as was the impact on the resistance or decreased susceptibility phenotype.Strains were selected in vitro under increasing ciprofloxacin concentrations. Etest and broth microdilution tests were used to determine the MICs of several unrelated compounds. Screening of mutations in the quinolone target genes and MDR regulators was performed. RT-PCR analysis was used to detect the levels of expression of acrB, tolC, ompF, acrF, emrB, acrR, ramA, soxS and marA.All mutant strains showed increased MICs of most of the antimicrobials tested, with the exception of kanamycin. Mutations in the quinolone target genes did not occur in all the mutants, which all harboured mutations in the ramRA regulatory region. All the mutants overexpressed ramA, tolC and acrB (only tested in 60-wt derivatives), whereas differential results were seen for the remaining genes.Mutations in the ramRA region related to resistance and/or decreased susceptibility to antimicrobials predominate in Salmonella. There is heterogeneity in the types of mutations, with deletions affecting RamR-binding sites having a greater impact on ramA expression and the MDR phenotype.