Nakanishi N, Yoshida S, Wakebe H, Inoue M, Mitsuhashi S
Episome Institute, Fujimimura, Gunma, Japan.
Antimicrob Agents Chemother. 1991 Jun;35(6):1053-9. doi: 10.1128/AAC.35.6.1053.
About 10% of 100 clinical isolates of Enterococcus faecalis were resistant to greater than or equal to 25 micrograms of norfloxacin, ofloxacin, ciprofloxacin, and temafloxacin per ml. In this study, the DNA gyrase of E. faecalis was purified from a fluoroquinolone-susceptible strain (ATCC 19433) and two resistant isolates, MS16968 and MS16996. Strains MS16968 and MS16996 were 64- to 128-fold and 16- to 32-fold less susceptible, respectively, to fluoroquinolones than was ATCC 19433; MICs of nonquinolone antibacterial agents for these strains were almost equal. The DNA gyrase from ATCC 19433 had two subunits, designated A and B, with properties similar to those of DNA gyrase from other gram-positive bacteria such as Bacillus subtilis and Micrococcus luteus. Inhibition of the supercoiling activity of the enzyme from ATCC 19433 by the fluoroquinolones correlated with their antibacterial activities. In contrast, preparations of DNA gyrase from MS16968 and MS16996 were at least 30-fold less sensitive to inhibition of supercoiling by the fluoroquinolones than the gyrase from ATCC 19433 was. Experiments that combined heterologous gyrase subunits showed that the A subunit from either of the resistant isolates conferred resistance to fluoroquinolones. These findings indicate that an alteration in the gyrase A subunit is the major contributor to fluoroquinolone resistance in E. faecalis clinical isolates. A difference in drug uptake may also contribute to the level of fluoroquinolone resistance in these isolates.
100株粪肠球菌临床分离株中，约10%对每毫升25微克及以上的诺氟沙星、氧氟沙星、环丙沙星和替马沙星耐药。在本研究中，从一株氟喹诺酮敏感菌株（ATCC 19433）以及两株耐药分离株MS16968和MS16996中纯化了粪肠球菌的DNA促旋酶。菌株MS16968和MS16996对氟喹诺酮的敏感性分别比ATCC 19433低64至128倍和16至32倍；这些菌株对非喹诺酮类抗菌剂的最低抑菌浓度几乎相同。来自ATCC 19433的DNA促旋酶有两个亚基，分别命名为A和B，其性质与来自其他革兰氏阳性菌如枯草芽孢杆菌和藤黄微球菌的DNA促旋酶相似。氟喹诺酮类药物对来自ATCC 19433的酶超螺旋活性的抑制作用与其抗菌活性相关。相比之下，来自MS16968和MS16996的DNA促旋酶制剂对氟喹诺酮类药物抑制超螺旋的敏感性至少比来自ATCC 19433的促旋酶低30倍。将异源促旋酶亚基组合的实验表明，任一耐药分离株的A亚基都赋予了对氟喹诺酮类药物的耐药性。这些发现表明，促旋酶A亚基的改变是粪肠球菌临床分离株对氟喹诺酮类药物耐药的主要原因。药物摄取的差异也可能导致这些分离株对氟喹诺酮类药物的耐药水平。
