Members of the small multidrug resistance (SMR) efflux pump family known as SugE (recently renamed Gdx) are known for their narrow substrate selectivity to small guanidinium (Gdm⁺) compounds and disinfectant quaternary ammonium compounds (QACs). Gdx members have been identified on multidrug resistance plasmids in Gram-negative bacilli, but their functional role remains unclear, as few have been characterized. Here, we conducted a survey of sequenced proteobacterial plasmids that encoded one or more SugE/Gdx sequences in an effort to (i) identify the most frequently represented Gdx member(s) on these plasmids and their sequence diversity, (ii) verify if Gdx sequences possess a Gdm⁺ riboswitch that regulates their translation similarly to chromosomally encoded Gdx members, and (iii) determine the antimicrobial susceptibility profile of the most predominate Gdx member to various QACs and antibiotics in Escherichia coli strains BW25113 and KAM32. The results of this study determined 14 unique SugE sequences, but only one Gdx sequence, annotated as “SugE(p),” predominated among the >140 plasmids we surveyed. Enterobacterales plasmids carrying sugE(p) possessed a guanidine II riboswitch similar to the upstream region of E. coli gdx. Cloning and expression of sugE(p), gdx, and emrE sequences into a low-copy-number expression vector (pMS119EH) revealed significant increases in QAC resistance to a limited range of detergent-like QACs only when gdx and sugE(p) transformants were grown as biofilms. These findings suggest that sugE(p) presence on proteobacterial plasmids may be driven by species that frequently encounter Gdm⁺ and QAC exposure.

中文翻译：

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核糖开关相关的胍选择性外排泵经常在变形菌质粒上传递，增加了大肠杆菌生物膜对消毒剂的耐受性。


小型多药耐药 (SMR) 外排泵家族的成员被称为 SugE（最近更名为 Gdx），因其对小型胍 (Gdm ⁺ ) 化合物和消毒剂季铵化合物 (QAC) 的底物选择性窄而闻名。已在革兰氏阴性杆菌的多药耐药质粒上鉴定出 Gdx 成员，但其功能作用仍不清楚，因为很少有人对其进行表征。在这里，我们对编码一个或多个 SugE/Gdx 序列的变形菌质粒进行了一项测序调查，以期 (i) 识别这些质粒上最常见的 Gdx 成员及其序列多样性，(ii) 验证 Gdx 是否序列拥有 Gdm ⁺核糖开关，与染色体编码的 Gdx 成员类似地调节其翻译，并且 (iii) 确定最主要的 Gdx 成员对大肠杆菌菌株 BW25113 和 KAM32 中各种 QAC 和抗生素的抗菌敏感性概况。这项研究的结果确定了 14 个独特的 SugE 序列，但只有一个注释为“SugE(p)”的 Gdx 序列在我们调查的 > 140 个质粒中占主导地位。携带sugE ( p )的肠杆菌质粒具有与大肠杆菌gdx上游区域类似的胍II核糖开关。将sugE ( p )、 gdx和emrE序列克隆并表达到低拷贝数表达载体 (pMS119EH) 中，结果表明，仅当gdx和sugE ( p ) 转化体时，QAC 对有限范围的去垢剂样 QAC 的抗性显着增加生长为生物膜。 这些发现表明，变形菌质粒上sugE ( p ) 的存在可能是由经常遇到 Gdm ⁺和 QAC 暴露的物种驱动的。