Department of Infection, Immunity and Inflammation, University of Leicester, Leicester, United Kingdom.
Antimicrob Agents Chemother. 2012 Apr;56(4):1845-53. doi: 10.1128/AAC.05334-11. Epub 2012 Jan 30.
Since the 2006 discovery of the Acinetobacter baumannii strain AYE AbaR1 resistance island, similar elements have been reported in numerous members of this species. As AbaR1 is distantly related to Tn7, we have renamed it TnAbaR1. TnAbaR transposons are known to carry multiple antibiotic resistance- and efflux-associated genes, although none have been experimentally studied en bloc. We deleted the TnAbaR transposon in A. baumannii A424, which we have designated TnAbaR23, and characterized independent deletion mutants DCO163 and DCO174. The NotI pulsed-field gel electrophoresis (PFGE) profile of strain DCO174 was consistent with targeted deletion of TnAbaR23 alone, but strain DCO163 apparently harbored a second large genomic deletion. Nevertheless, "subtractive amplification" targeting 52 TnAbaR and/or resistance-associated loci yielded identical results for both mutants and highlighted genes lost relative to strain A424. PCR mapping and genome sequencing revealed the entire 48.3-kb sequence of TnAbaR23. Consistent with TnAbaR23 carrying two copies of sul1, both mutants exhibited markedly increased susceptibility to sulfamethoxazole. In contrast, loss of tetAR(A) resulted in only a minor and variable increase in tetracycline susceptibility. Despite not exhibiting a growth handicap, strain DCO163 was more susceptible than strain DCO174 to 9 of 10 antibiotics associated with mutant-to-mutant variation in susceptibility, suggesting impairment of an undefined resistance-associated function. Remarkably, despite all three strains sharing identical gyrA and parC sequences, the ciprofloxacin MIC of DCO174 was >8-fold that of DCO163 and A424, suggesting a possible paradoxical role for TnAbaR23 in promoting sensitivity to ciprofloxacin. This study highlights the importance of experimental scrutiny and challenges the assumption that resistance phenotypes can reliably be predicted from genotypes alone.
自 2006 年发现鲍曼不动杆菌 AYE AbaR1 抗性岛以来，在该物种的许多成员中都报道了类似的元件。由于 AbaR1 与 Tn7 关系较远，我们将其重新命名为 TnAbaR1。已知 TnAbaR 转座子携带多种抗生素耐药性和外排相关基因，尽管尚未对其进行过整体实验研究。我们删除了鲍曼不动杆菌 A424 中的 TnAbaR 转座子，将其命名为 TnAbaR23，并对独立缺失突变体 DCO163 和 DCO174 进行了表征。菌株 DCO174 的 NotI 脉冲场凝胶电泳 (PFGE) 图谱与 TnAbaR23 单独缺失一致，但菌株 DCO163 显然携带第二个较大的基因组缺失。然而，针对 52 个 TnAbaR 和/或耐药相关基因的“减法扩增”，对两个突变体均产生了相同的结果，并突出了相对于菌株 A424 丢失的基因。PCR 图谱和基因组测序揭示了 TnAbaR23 的整个 48.3kb 序列。与 TnAbaR23 携带两个 sul1 拷贝一致，两个突变体对磺胺甲恶唑的敏感性显著增加。相比之下，tetAR(A) 的缺失仅导致四环素敏感性略有且可变增加。尽管没有表现出生长障碍，但与抗生素敏感性突变体之间的变异相关的 10 种抗生素中的 9 种，菌株 DCO163 比菌株 DCO174 更敏感，这表明一种未定义的耐药相关功能受损。值得注意的是，尽管这三个菌株都具有相同的 gyrA 和 parC 序列，但 DCO174 的环丙沙星 MIC 是 DCO163 和 A424 的 8 倍以上，这表明 TnAbaR23 可能对环丙沙星的敏感性具有矛盾作用。本研究强调了实验审查的重要性，并对仅从基因型可靠预测耐药表型的假设提出了挑战。
