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The short-term aerosol administration of a high dose of tobramycin in patients with clinically stable cystic fibrosis is an efficacious and safe treatment for endobronchial infection with P. aeruginosa.

We conducted a double-blind, placebo-controlled, multicenter, randomized trial to test the hypothesis that 300 mg of tobramycin solution for inhalation administered twice daily for 28 days would be safe and result in a profound decrease in Pseudomonas aeruginosa (Pa) density from the lower airway of young children with cystic fibrosis. Ninety-eight subjects were to be randomized; however, the trial was stopped early because of evidence of a significant microbiological treatment effect. Twenty-one children under age 6 years were randomized (8 active; 13 placebo) and underwent bronchoalveolar lavage at baseline and on Day 28. There was a significant difference between treatment groups in the reduction in Pa density; no Pa was detected on Day 28 in 8 of 8 active group patients compared with 1 of 13 placebo group patients. We observed no differences between treatment groups for clinical indices, markers of inflammation, or incidence of adverse events. No abnormalities in serum creatinine or audiometry and no episodes of significant bronchospasm were observed in association with active treatment. We conclude that 28 days of tobramycin solution for inhalation of 300 mg twice daily is safe and effective for significant reduction of lower airway Pa density in young children with cystic fibrosis.

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A Pseudomonas aeruginosa oxyR mutant was dramatically sensitive to H 2 O 2 , despite possessing wild-type catalase activity. Oxygen-dependent oxyR phenotypes also included an inability to survive aerobic serial dilution in Luria broth and to resist aminoglycosides. Plating the oxyR mutant after serial dilution in its own spent culture supernatant, which contained the major catalase KatA, or under anaerobic conditions allowed for survival. KatA was resistant to sodium dodecyl sulfate, proteinase K, pepsin, trypsin, chymotrypsin and the neutrophil protease cathepsin G. When provided in trans and expressed constitutively, the OxyR-regulated genes katB, ahpB, and ahpCF could not restore both the serial dilution defect and H 2 O 2 resistance; only oxyR itself could do so. The aerobic dilution defect could be complemented, in part, by only ahpB and ahpCF, suggesting that the latter gene products could possess a catalase-like activity. Aerobic Luria broth was found to generate ϳ1.2 M H 2 O 2 min ؊1 via autoxidation, a level sufficient to kill serially diluted oxyR and oxyR katA bacteria and explain the molecular mechanism behind the aerobic serial dilution defect. Taken together, our results indicate that inactivation of OxyR renders P. aeruginosa exquisitely sensitive to both H 2 O 2 and aminoglycosides, which are clinically and environmentally important antimicrobials.The major response of Escherichia coli to hydrogen peroxide (H 2 O 2 ) is governed by a 34-kDa transactivator, OxyR (5,6,30,31). OxyR positively regulates katG (encoding hydroperoxidase I), gorA (encoding glutathione reductase), ahpCF (encoding alkyl hydroperoxide reductase), dps (encoding a nonspecific DNA-binding protein) (1, 5, 6), and fur (encoding ferric uptake regulatory protein) (31). Each of these genes is important in combating H 2 O 2 -mediated stress. OxyR acts as a transcriptional autorepressor under noninducing conditions. However, in the presence of its inducer, H 2 O 2 , an intramolecular disulfide bond that activates OxyR is formed, allowing it to then govern transcription of OxyR-dependent promoters (24,26).In contrast to the case for E. coli, genes under OxyR control in Pseudomonas aeruginosa include the katB-ankB operon, ahpB, and ahpCF (17). These genes encode catalase B (KatB), an ankyrin-like protein that is necessary for optimal KatB activity (AnkB), and two alkyl hydroperoxide reductases, AhpB and AhpCF, respectively (17). In this work, we report dramatic sensitivity of a P. aeruginosa oxyR mutant to H 2 O 2 and aminoglycosides, despite possessing wild-type catalase activity. Growth of serially diluted oxyR organisms under aerobic conditions was found to require the major housekeeping catalase, KatA, which was released into the extracellular milieu upon cell lysis. KatA was found to be resistant to a number of proteases, including the human neutrophil serine protease cathepsin G. Our data suggest that released KatA could remain for extended periods, especially in P. aeruginosa biofilms of environmental, industrial, and clinical i...

Factors other than mutations in the CFTR gene can produce phenotypes clinically indistinguishable from nonclassic cystic fibrosis caused by CFTR dysfunction.

Chronic endobronchial bacterial infection evokes purulent airway secretions in patients with CF. The viscoelastic properties of these secretions is primarily due to the presence of polymerized DNA from degenerating leukocytes. Recombinant human DNase I (rhDNase) reduces the viscosity of CF sputum in vitro. To test the hypothesis that rhDNase would improve pulmonary function in children and adults with CF, we compared the efficacy and safety of 10-day administration of three doses of aerosolized rhDNase (0.6, 2.5, or 10.0 mg twice daily) in 181 outpatients using a randomized, placebo-controlled parallel design. Forced vital capacity (FVC) improved 10 to 12% (p < 0.05 to 0.001), and forced expiratory volume in one second (FEV1) improved 10 to 15% (p < 0.001) across all doses of rhDNase compared with placebo. The magnitude of effect was dose dependent for both FVC and FEV1 through study Day 21 (p < 0.001). rhDNase was associated with a decreased perception of dyspnea and an improved perception of well-being. No patients developed detectable anti-rhDNase antibodies or bronchial reactivity to rhDNase. Some patients experienced mild upper airway irritation, but no major adverse events were reported. Administration for 10 days of aerosolized rhDNase to pediatric and adult outpatients with CF improves lung function and is well tolerated. Although all three doses were efficacious, the greatest improvement in FEV1 and FEV1/FVC ratio was demonstrated in the 2.5 and 10.0 mg rhDNase treatment groups.

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