Hyperoxia and prolongation of aminoglycoside-induced postantibiotic effect in Pseudomonas aeruginosa: role of reactive oxygen species

Abstract

Hyperoxia prolongs the postantibiotic effect (PAE) of the aminoglycoside tobramycin in Pseudomonas aeruginosa. We tested the hypothesis that the PAE is prolonged because hyperoxia increases free radical flux while tobramycin inhibits the induction of antioxidant defenses. Exposure ofP. aeruginosa to hyperoxia (100%O 02) for 1 h increased superoxide dismutase, catalase, and glutathione levels. In the presence of tobramycin (1 x the MIC), the induction of antioxidant defenses by hyperoxia was nearly abrogated. Neither preexposure ofP. aeruginosa to hyperoxia nor supplementation with the antioxidants copper(II) (diisopropylsalicylate)2 (superoxide dismutase-like), catalase, or dimethyl sulfoxide abolished prolongation of the PAE of tobramycin induced by hyperoxia.We recently showed that hyperoxia acts in synergy with an aminoglycoside antibiotic to prolong the postantibiotic effect (PAE) of tobramycin against Pseudomonas aeruginosa (18). The PAE describes the period of bacterial growth suppression that results from a brief exposure to an antimicrobial agent (14). For aminoglycosides, the PAE represents the time required for synthesis of new ribosomes (4).Hyperoxia increases the intracellular flux of 02 and other reactive oxygen species (8). In the study described here, we tested the hypothesis that hyperoxia enhances the PAE of tobramycin against P. aeruginosa by increasing the intracel- MIC of tobramycin for P. aeruginosa ATCC 27853 was 0.5 p,g/ml.The antioxidant enzymes and free radical scavengers were used at the highest concentration which did not inhibit bacterial growth, namely, CuDIPS at 1 x 10-4 M, CAT at 4 x 10' M, and DMSO at 0.4 M. The antioxidants were added before exposure to hyperoxia. The PAE was measured as described previously (18).For enymatic and thiol assays, bacteria (final concentration, -10' CFU/ml) were grown for 2 h in a shaking water bath under ambient conditions (21% 02, 37°C, 100 rpm) before a 1-h exposure to hyperoxia and/or tobramycin (lx the MIC). Bacteria were then filtered onto 0.2-,m-pore-size filters, washed, and resuspended in 50 mM phosphate buffer (pH 7.0); filters were removed after vortexing. Bacteria were centrifuged at 10,000 x g for 15 min at 4°C. After decanting and resuspending with 50 mM phosphate buffer (pH 7.0) with 0.1 mM EDTA, bacterial cells were lysed by sonication (model W185 sonifier; Branson, Plainview, N.Y.) at 60 W (45 s, eight times). Membranes were sedimented by centrifugation at 27,500 x g for 30 min.

Reactive Oxygen Species Production Is a Major Factor Directing the Postantibiotic Effect of Fluoroquinolones in Streptococcus pneumoniae

“…Production of ROS was also recently suggested as the mechanism of antibacterial and antibiofilm activity of other drugs, such as thymoquinone (24), ciprofloxacin, and meropenem (25). Previous studies also related ROS increases with longer PAEs induced by aminoglycosides in Pseudomonas aeruginosa under hyperoxic conditions (26). The photolysis of hydrogen peroxide induced significantly longer PAE in Staphylococcus aureus and Streptococcus salivarius due to the generation of hydroxyl radicals (27).…”

Positive effects of hyperbaric oxygen therapy in a cat with cutaneous nocardiosis

“…6 Hyperoxic states also can potentiate the activity of aminoglycosides, prolong the postantibiotic effect, form free radicals with bactericidal effects and stimulate phagocytosis. 2,7 Amikacin was selected as empirical treatment in this case owing to easier administration and the proportionally high number of cats with nocardiosis displaying susceptibility to amikacin. 1 Thrice-weekly dosing has been reported in treating Mycobacteria spp.…”

Postantibiotic effect in vitro

“…It has been noted that the duration of PAE was increased for ciprofloxacin against Staphylococcus aureus in media at an acid or alkalic pH compared to broth at pH 7.4, while a reduction in duration of PAE was observed, at an acid pH, for imipenem, ciprofloxacin and aminoglycosides against Echerichia coli and Pseudomonas aeruginosa (Thorburn et al 1996), and no effect of pH was observed for dicloxacillin or gentamicin against Staphylococcus aureus (Gudmundsson et al 1991;. The concentration of Mg2+ has been demonstrated to influence duration of PAE with ofloxacin (Gurdal et al 1990) and hyperbaric oxygen increased PAE twofold when Pseudomonas aeruginosa was treated with tobramycin (Park et al 1991;Park et al 1993). In contrast, a temperature above 37°C had only minimal effects on duration of PAE (Magnusson et al 1995).…”