Park B H, Hendricks M, Malamy M H, Tally F P, Levy S B
Department of Molecular Biology, Tufts University School of Medicine, Boston, Massachusetts 02111.
Antimicrob Agents Chemother. 1987 Nov;31(11):1739-43. doi: 10.1128/AAC.31.11.1739.
Escherichia coli bearing a cryptic tetracycline resistance determinant from Bacteroides fragilis expressed low-level constitutive resistance to tetracycline under aerobic, but not anaerobic, growth conditions and accumulated less tetracycline aerobically than did isogenic susceptible cells. This decreased uptake was energy dependent and reversible by increased concentrations of tetracycline, suggesting a saturable carrier-mediated active efflux mechanism. Decreased uptake was not seen when the cells were grown and assayed anaerobically. Other tetracycline resistance determinants (classes A to E) isolated from gram-negative enteric bacteria expressed resistance and generated active efflux of tetracycline under anaerobic as well as aerobic conditions. When the Bacteroides determinant was placed in the same cell with any of the class A to E tetracycline resistance determinants, there was an increase in resistance under aerobic conditions of as much as 48% more than was projected by adding the resistances expressed by the determinants individually. In cells bearing the class A determinant together with the Bacteroides determinant, saturation of the active efflux system required over twofold more exogenous tetracycline than did cells bearing the class A determinant alone. We have designated this new tetracycline resistance determinant class F.
携带来自脆弱拟杆菌的隐性四环素抗性决定簇的大肠杆菌在有氧生长条件下对四环素表现出低水平的组成型抗性，但在厌氧生长条件下则不然，并且与同基因敏感细胞相比，有氧条件下积累的四环素更少。这种摄取减少是能量依赖性的，并且可以通过增加四环素浓度来逆转，这表明存在一种可饱和的载体介导的主动外排机制。当细胞在厌氧条件下生长和检测时，未观察到摄取减少。从革兰氏阴性肠道细菌中分离出的其他四环素抗性决定簇（A至E类）在厌氧和好氧条件下均表现出抗性并产生四环素的主动外排。当拟杆菌决定簇与A至E类四环素抗性决定簇中的任何一个置于同一细胞中时，在有氧条件下的抗性增加比单独添加决定簇所表达的抗性预计值高出多达48%。在携带A类决定簇和拟杆菌决定簇的细胞中，与仅携带A类决定簇的细胞相比，主动外排系统的饱和需要两倍多的外源性四环素。我们将这种新的四环素抗性决定簇命名为F类。
