Center of Excellence for Infection Control Science, Graduate School of Medicine, Juntendo University, 2-1-1 Hongo, Bunkyo-ku, Tokyo 113-8421, Japan.
Department of Bacteriology, Faculty of Medicine, Juntendo University, 2-1-1 Hongo, Bunkyo-ku, Tokyo 113-8421, Japan.
Int J Antimicrob Agents. 2015 Dec;46(6):666-73. doi: 10.1016/j.ijantimicag.2015.09.006. Epub 2015 Oct 22.
We previously reported the first 'reverse antibiotic' (RA), nybomycin (NYB), which showed a unique antimicrobial activity against Staphylococcus aureus strains. NYB specifically suppressed the growth of quinolone-resistant S. aureus strains but was not effective against quinolone-susceptible strains. Although NYB was first reported in 1955, little was known about its unique antimicrobial activity because it was before the synthesis of the first quinolone ('old quinolone'), nalidixic acid, in 1962. Following our re-discovery of NYB, we looked for other RAs among natural substances that act on quinolone-resistant bacteria. Commercially available flavones were screened against S. aureus, including quinolone-resistant strains, and their minimum inhibitory concentrations (MICs) were compared using the microbroth dilution method. Some of the flavones screened showed stronger antimicrobial activity against quinolone-resistant strains than against quinolone-susceptible ones. Amongst them, apigenin (API) was the most potent in its RA activity. DNA cleavage assay showed that API inhibited DNA gyrase harbouring the quinolone resistance mutation gyrA(Ser84Leu) but did not inhibit 'wild-type' DNA gyrase that is sensitive to levofloxacin. An API-susceptible S. aureus strain Mu50 was also selected using agar plates containing 20mg/L API. Whole-genome sequencing of selected mutant strains was performed and frequent back-mutations (reverse mutations) were found among API-resistant strains derived from the API-susceptible S. aureus strains. Here we report that API represents another molecular class of natural antibiotic having RA activity against quinolone-resistant bacteria.
我们之前报道了第一个“反向抗生素”（RA），奈博霉素（NYB），它对金黄色葡萄球菌表现出独特的抗菌活性。NYB 特异性抑制耐喹诺酮金黄色葡萄球菌株的生长，但对耐喹诺酮敏感株无效。尽管 NYB 于 1955 年首次报道，但由于它是在 1962 年合成第一个喹诺酮（“旧喹诺酮”）萘啶酸之前，因此对其独特的抗菌活性知之甚少。在重新发现 NYB 之后，我们在作用于耐喹诺酮细菌的天然物质中寻找其他 RA。使用微量肉汤稀释法筛选了针对金黄色葡萄球菌（包括耐喹诺酮株）的市售黄酮类化合物，并比较了它们的最小抑菌浓度（MIC）。筛选出的一些黄酮类化合物对耐喹诺酮株的抗菌活性强于对耐喹诺酮株。其中，芹菜素（API）在其 RA 活性中最有效。DNA 切割实验表明，API 抑制携带喹诺酮耐药突变 gyrA（Ser84Leu）的 DNA 回旋酶，但不抑制对左氧氟沙星敏感的“野生型”DNA 回旋酶。还使用含有 20mg/L API 的琼脂平板选择了 API 敏感的金黄色葡萄球菌 Mu50 菌株。对选择的突变菌株进行了全基因组测序，发现源自 API 敏感金黄色葡萄球菌菌株的 API 耐药菌株中频繁发生反向突变（回复突变）。在这里，我们报告 API 代表了另一种具有针对耐喹诺酮细菌的 RA 活性的天然抗生素分子类别。
