Department of Veterinary Pathology and Microbiology, University of Nigeria, Nsukka, Nigeria.
Department of Pathology and Infectious Diseases, Royal Veterinary College, University of London, London, England, United Kingdom.
PLoS One. 2020 Jul 6;15(7):e0235633. doi: 10.1371/journal.pone.0235633. eCollection 2020.
The antibacterial efficacy of the tetracycline antibiotics has been greatly reduced by the development of resistance, hence a decline in their clinical use. The hok/sok locus is a type I toxin/antitoxin plasmid stability element, often associated with multi-drug resistance plasmids, especially ESBL-encoding plasmids. It enhances host cell survivability and pathogenicity in stressful growth conditions, and increases bacterial tolerance to β-lactam antibiotics. The hok/sok locus forms dsRNA by RNA:RNA interactions between the toxin encoding mRNA and antitoxin non-coding RNA, and doxycycline has been reported to bind dsRNA structures and inhibit their cleavage/processing by the dsRNase, RNase III. This study investigated the antibacterial activities of doxycycline in hok/sok host bacteria cells, the effects on hok/sok-induced changes in growth and the mechanism(s) involved. Diverse strains of E. coli were transformed with hok/sok plasmids and assessed for doxycycline susceptibility and growth changes. The results show that the hok/sok locus increases bacterial susceptibility to doxycycline, which is more apparent in strains with more pronounced hok/sok-induced growth effects. The increased doxycycline susceptibility occurs despite β-lactam resistance imparted by hok/sok. Doxycycline was found to induce bacterial death in a manner phenotypically characteristic of Hok toxin expression, suggesting that it inhibits the toxin/antitoxin dsRNA degradation, leading to Hok toxin expression and cell death. In this way, doxycycline could counteract the multi-drug resistance plasmid maintenance/propagation, persistence and pathogenicity mechanisms associated with the hok/sok locus, which could potentially help in efforts to mitigate the rise of antimicrobial resistance.
四环素有较强的抗菌功效，但其耐药性的发展大大降低了其临床应用。hok/sok 基因座是一种 I 型毒素/抗毒素质粒稳定性元件，通常与多药耐药质粒有关，尤其是编码 ESBL 的质粒。它增强了宿主细胞在应激生长条件下的生存能力和致病性，并增加了细菌对β-内酰胺类抗生素的耐受性。hok/sok 基因座通过毒素编码 mRNA 与抗毒素非编码 RNA 之间的 RNA:RNA 相互作用形成 dsRNA，并且已经报道强力霉素结合 dsRNA 结构并抑制 dsRNase、RNase III 对其的切割/加工。本研究调查了强力霉素在 hok/sok 宿主细菌细胞中的抗菌活性、对 hok/sok 诱导的生长变化的影响及其涉及的机制。将不同的大肠杆菌菌株转化为 hok/sok 质粒，并评估其对强力霉素的敏感性和生长变化。结果表明，hok/sok 基因座增加了细菌对强力霉素的敏感性，在 hok/sok 诱导的生长效应更为明显的菌株中更为明显。尽管 hok/sok 赋予了β-内酰胺耐药性，但增加的强力霉素敏感性仍然存在。强力霉素被发现以表型上类似于 Hok 毒素表达的方式诱导细菌死亡，这表明它抑制了毒素/抗毒素 dsRNA 的降解，导致 Hok 毒素的表达和细胞死亡。通过这种方式，强力霉素可以对抗与 hok/sok 基因座相关的多药耐药质粒维持/传播、持久性和致病性机制，这可能有助于减轻抗菌药物耐药性的上升。
