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Bacteria and fungi show substantial increased recalcitrance when growing as infectious biofilms. Chronic infections caused by biofilm growing microorganisms is considered a major problem of modern medicine. New strategies are needed to improve antibiotic treatment of biofilms. We have improved antibiotic treatment of bacterial biofilms by reviving the dormant bacteria and thereby make them susceptible to antibiotics by means of reoxygenation. Here we review the rationale for associating lack of oxygen with low susceptibility in infectious biofilm, and how hyperbaric oxygen therapy may result in reoxygenation leading to enhanced bactericidal activity of antibiotics. We address issues of feasibility and potential adverse effects regarding patient safety and development of resistance. Finally, we propose means for supplying reoxygenation to antibiotic treatment of infectious biofilm with the potential to benefit large groups of patients.

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BACKGROUND: Early signs of Mycobacterium avium complex pulmonary disease can be missed in patients with cystic fibrosis due to subclinical infection or delays in mycobacterial culture. The aim of this study was to determine the diagnostic accuracy of a novel enzyme linked immunosorbent assay for immunoglobulin G against Mycobacterium avium complex, which could help stratify patients according to risk. METHODS: A retrospective cross sectional analysis of serum samples from the Copenhagen Cystic Fibrosis Center was performed. Corresponding clinical data were reviewed and patients with cystic fibrosis were assigned to one of four groups based on their mycobacterial culture results. In addition, anti-Mycobacterium avium complex immunoglobulin G levels were measured longitudinally before and after first positive culture in the period 1984-2015. RESULTS: Three-hundred and five patients with cystic fibrosis were included with a median of five nontuberculous mycobacterial cultures. Four individuals had Mycobacterium avium complex pulmonary disease at the time of cross sectional testing and their median antibody level was 22-fold higher than patients with no history of infection (1820 vs. 80 IgG units; p < 0.001). Test sensitivity was 100% (95% CI 40-100) and specificity 77% (95% CI 72-81). Longitudinal kinetics showed rising antibodies prior to first positive culture suggesting diagnostic delay. CONCLUSIONS: Antibody screening for Mycobacterium avium complex may be used as a supplement to culture. Although confirmation in a larger cohort is needed, our findings suggest that stratifying a cystic fibrosis population into high- and low-risk groups based on antibody levels may help clinicians identify patients in need of more frequent culture.

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Staphylococcus aureus infective endocarditis (IE) is a serious disease with an in-hospital mortality of up to 40%. Improvements in the effects of antibiotics and host responses could potentially benefit outcomes. Hyperbaric oxygen therapy (HBOT) represents an adjunctive therapeutic option. In this study, the efficacy of HBOT in combination with tobramycin in S. aureus IE was evaluated. A rat model of S. aureus IE mimicking the bacterial load in humans was used. Infected rats treated subcutaneously with tobramycin were randomised into two groups: (i) HBOT twice daily (n = 13); or (ii) normobaric air breathing (non-HBOT) (n = 17). Quantitative bacteriology, cytokine expression, valve vegetation size and clinical status were assessed 4 days post-infection. Adjunctive HBOT reduced the bacterial load in the aortic valves, myocardium and spleen compared with the non-HBOT group (P = 0.004, <0.001 and 0.01, respectively) and improved the clinical score (P <0.0001). Photoplanimetric analysis and weight of valve vegetations showed significantly reduced vegetations in the HBOT group (P <0.001). Key pro-inflammatory cytokines [IL-1ß, IL-6, keratinocyte-derived chemokine (KC) and vascular endothelial growth factor (VEGF)] were significantly reduced in valves from the HBOT group compared with the non-HBOT group. In conclusion, HBOT augmented tobramycin efficacy as assessed by several parameters. These findings suggest the potential use of adjunctive therapy in severe S. aureus IE.

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Chronic Pseudomonas aeruginosa lung infection in cystic fibrosis (CF) patients is characterized by persisting mucoid biofilms in hypoxic endobronchial mucus. These biofilms are surrounded by numerous polymorphonuclear leucocytes (PMNs), which consume a major part of present molecular oxygen (O(2)) due to production of superoxide (O(2)(-)). In this study, we show that the PMNs also consume O(2) for production of nitric oxide (NO) by the nitric oxide synthases (NOS) in the infected endobronchial mucus. Fresh expectorated sputum samples (n = 28) from chronically infected CF patients (n = 22) were analysed by quantifying and visualizing the NO production. NO production was detected by optode measurements combined with fluorescence microscopy, flow cytometry and spectrophotometry. Inhibition of nitric oxide synthases (NOS) with N(G) -monomethyl-L-arginine (L-NMMA) resulted in reduced O(2) consumption (P < 0·0008, n = 8) and a lower fraction of cells with fluorescence from the NO-indicator 4-amino-5-methylamino-2',7'-difluorofluorescein diacetate (DAF-FM) (P < 0·002, n = 8). PMNs stained with DAF-FM and the superoxide indicator hydroethidine (HE) and host cells with inducible NOS (iNOS) were identified in the sputum. In addition, the production of the stable end-products of NO in CF sputum was correlated with the concentration of PMNs; NO(3)(-) (P < 0·04, r = 0·66, n = 10) and NO(2)(-) (P< 0·006, r = 0·78, n = 11). The present study suggests that besides consumption of O(2) for production of reactive oxygen species, the PMNs in CF sputum also consume O(2) for production of NO.

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BACKGROUND: Chronic lung infection with Pseudomonas aeruginosa is the most severe complication for patients with cystic fibrosis (CF). This infection is characterised by endobronchial mucoid biofilms surrounded by numerous polymorphonuclear leucocytes (PMNs). The mucoid phenotype offers protection against the PMNs, which are in general assumed to mount an active respiratory burst leading to lung tissue deterioration. An ongoing respiratory burst by the PMNs has, however, not been demonstrated previously in endobronchial secretions from chronically infected patients with CF. OBJECTIVE: Based on the accumulating evidence for depletion of molecular oxygen (O(2)) in the mucus in infected CF bronchi, it was hypothesised that the O(2) depletion in the mucus in infected CF bronchi may be accelerated by the respiratory burst of the PMNs due to the reduction of O(2) to the superoxide anion (O(-)(2)) by the phagocyte NADPH oxidase (Phox). METHODS: Methods were established to isolate the O(2) consumption by the respiratory burst from aerobic respiration in freshly expectorated sputum from chronically infected patients with CF. RESULTS: Inhibition of the Phox with diphenylene iodonium (DPI) delayed O(2) depletion, nearly abolished staining of O(-)(2)-producing PMNs with hydroethidine and inhibited the rapid luminol-enhanced chemiluminescence in sputum. Furthermore, the total O(2) consumption was correlated to the concentration of PMNs in the sputum samples. CONCLUSION: The results demonstrate that CF sputum contains PMNs with an active consumption of O(2) for O(-)(2) production and suggest that the respiratory burst is ongoing and causes accelerated O(2) depletion due to formation of O(-)(2) in the lungs of chronically infected patients with CF.

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