Cohn R C, Aronoff S C
Department of Pediatrics, Children's Medical Center, Dayton, OH 45404.
J Lab Clin Med. 1989 Dec;114(6):724-7.
Amiloride combined with subinhibitory concentrations of tobramycin is synergistic against Pseudomonas cepacia in vitro. It is known that amiloride blocks transmembrane sodium (Na+) flux in eukaryotic cells, but the mechanism of action in bacteria is unknown. Amiloride-mediated Na+ gradient changes might affect transcellular tobramycin transport, resulting in synergy between these two drugs. To examine this hypothesis, we studied the effect of extracellular [Na+] on amiloride-tobramycin synergy with a reference strain of P. cepacia. Control growth in Mueller-Hinton broth (MHB) alone, MHB supplemented with 200 mmol/L NaCl, and MHB dialyzed against a Na+-free solution was determined by absorbance at 650 nm over 3 hours. Inhibition in the presence of amiloride, tobramycin, or a combination was expressed as percentage of control growth. Growth in the presence of tobramycin alone was significantly higher in MHB + NaCl than in MHB or dialyzed MHB (81% +/- 5%; vs 57% +/- 5%; 35% +/- 4%; mean +/- SEM, respectively, p = 0.003). Growth in the presence of amiloride alone was not significantly different in the three media (84% +/- 4%; 80% +/- 3%; 80% +/- 1%; respectively, p = 0.746). Percent control growth was significantly lower when the two drugs were combined, but results were not statistically different among the three media (3.5% +/- 3%; 0.2% +/- 0.8%; 4% +/- 1%; respectively, p = 0.604). We conclude that growth inhibition of P. cepacia in the presence of tobramycin is antagonized by increasing extracellular [Na+]. This antagonistic effect of [Na+] is reversed by amiloride. Changes in [Na+] do not appear to directly affect amiloride-tobramycin synergy in P. cepacia.
在体外，阿米洛利与亚抑菌浓度的妥布霉素联合使用对洋葱伯克霍尔德菌具有协同作用。已知阿米洛利可阻断真核细胞中的跨膜钠（Na⁺）通量，但在细菌中的作用机制尚不清楚。阿米洛利介导的Na⁺梯度变化可能会影响妥布霉素的跨细胞转运，从而导致这两种药物之间产生协同作用。为了验证这一假设，我们使用一株洋葱伯克霍尔德菌参考菌株研究了细胞外[Na⁺]对阿米洛利 - 妥布霉素协同作用的影响。通过在3小时内测定650nm处的吸光度来确定单独在 Mueller-Hinton肉汤（MHB）、添加200 mmol/L NaCl的MHB以及用无Na⁺溶液透析的MHB中的对照生长情况。在存在阿米洛利、妥布霉素或两者组合的情况下的抑制作用表示为对照生长的百分比。单独存在妥布霉素时，在MHB + NaCl中的生长明显高于在MHB或透析后的MHB中（分别为81%±5%；vs 57%±5%；35%±4%；平均值±标准误，p = 0.003）。单独存在阿米洛利时，在三种培养基中的生长没有显著差异（分别为84%±4%；80%±3%；80%±1%；p = 0.746）。当两种药物联合使用时，对照生长百分比显著降低，但在三种培养基中的结果在统计学上没有差异（分别为3.5%±3%；0.2%±0.8%；4%±1%；p = 0.604）。我们得出结论，增加细胞外[Na⁺]会拮抗妥布霉素存在时洋葱伯克霍尔德菌的生长抑制。[Na⁺]的这种拮抗作用可被阿米洛利逆转。[Na⁺]的变化似乎不会直接影响洋葱伯克霍尔德菌中阿米洛利 - 妥布霉素的协同作用。
