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Abstract：
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. coligdx 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.IMPORTANCE This study characterized the function of antimicrobial-resistant phenotypes attributed to plasmid-encoded guanidinium-selective small multidrug resistance (Gdm/SugE) efflux pumps. These sequences are frequently monitored as biocide resistance markers in antimicrobial resistance surveillance studies. Our findings reveal that enterobacterial gdm sequences transmitted on plasmids possess a guanidine II riboswitch, which restricts transcript translation in the presence of guanidinium. Cloning and overexpression of this gdm sequence revealed that it confers higher resistance to quaternary ammonium compound (QAC) disinfectants (which possess guanidium moieties) when grown as biofilms. Since biofilms are commonly eradicated with QAC-containing compounds, the presence of this gene on plasmids and its biofilm-specific resistance are a growing concern for clinical and food safety prevention measures.
摘要：
称为SugE（最近更名为Gdx）的小型多药耐药性（SMR）外排泵家族的成员因其对小胍（Gdm）化合物和消毒剂季铵化合物（QAC）的窄底物选择性而闻名。已经在革兰氏阴性杆菌的多药耐药质粒上鉴定了Gdx成员，但是它们的功能作用仍然不清楚，很少有人被定性。这里,我们对编码一个或多个SugE/Gdx序列的已测序的蛋白质质粒进行了调查，以（i）鉴定这些质粒上最常见的Gdx成员及其序列多样性，（ii）验证Gdx序列是否具有与染色体编码的Gdx成员类似地调节其翻译的Gdm核糖开关，和（iii）确定最主要的Gdx成员对大肠杆菌菌株BW25113和KAM32中各种QAC和抗生素的抗微生物剂敏感性。这项研究的结果确定了14个独特的SugE序列，但只有一个Gdx序列,注释为“SugE（p），“在我们调查的>140个质粒中占主导地位。携带sugE（p）的肠杆菌质粒具有类似于大肠杆菌上游区域的胍II核开关sugE（p）的克隆和表达，gdx,和低拷贝数表达载体（pMS119EH）中的emrE序列显示，只有当gdx和sugE（p）转化体生长为生物膜时，QAC对有限范围的去污剂样QAC的抗性才显着增加。这些发现表明，在蛋白质质粒上存在sugE（p）可能是由经常遇到Gdm和QAC暴露的物种驱动的。重要性本研究表征了归因于质粒编码的胍选择性小多药耐药性（Gdm/SugE）外排泵的抗微生物耐药表型的功能。这些序列经常作为抗微生物剂抗性监测研究中的抗微生物剂抗性标记物被监测。我们的发现表明，在质粒上传递的肠杆菌gdm序列具有胍II核开关，这限制了在胍存在下的转录本翻译。该gdm序列的克隆和过表达表明，当生长为生物膜时，它对季铵化合物（QAC）消毒剂（具有胍部分）具有更高的抗性。由于生物膜通常被含QAC的化合物根除，该基因在质粒上的存在及其生物膜特异性抗性是临床和食品安全预防措施日益关注的问题。
