Influence of macrolides on mucoid alginate biosynthetic enzyme from Pseudomonas aeruginosa

Recent Advances in Antimicrobial Nano-Drug Delivery Systems

Infectious diseases are among the major health issues of the 21st century. The substantial use of antibiotics over the years has contributed to the dissemination of multidrug resistant bacteria. According to a recent report by the World Health Organization, antibacterial (ATB) drug resistance has been one of the biggest challenges, as well as the development of effective long-term ATBs. Since pathogens quickly adapt and evolve through several strategies, regular ATBs usually may result in temporary or noneffective treatments. Therefore, the demand for new therapies methods, such as nano-drug delivery systems (NDDS), has aroused huge interest due to its potentialities to improve the drug bioavailability and targeting efficiency, including liposomes, nanoemulsions, solid lipid nanoparticles, polymeric nanoparticles, metal nanoparticles, and others. Given the relevance of this subject, this review aims to summarize the progress of recent research in antibacterial therapeutic drugs supported by nanobiotechnological tools.

Sub-Inhibitory Antibiotic Exposure and Virulence in Pseudomonas aeruginosa

Pseudomonas aeruginosa is a prime opportunistic pathogen, one of the most important causes of hospital-acquired infections and the major cause of morbidity and mortality in cystic fibrosis lung infections. One reason for the bacterium's pathogenic success is the large array of virulence factors that it can employ. Another is its high degree of intrinsic and acquired resistance to antibiotics. In this review, we first summarise the current knowledge about the regulation of virulence factor expression and production. We then look at the impact of sub-MIC antibiotic exposure and find that the virulence-antibiotic interaction for P. aeruginosa is antibiotic-specific, multifaceted, and complex. Most studies undertaken to date have been in vitro assays in batch culture systems, involving short-term (<24 h) antibiotic exposure. Therefore, we discuss the importance of long-term, in vivo-mimicking models for future work, particularly highlighting the need to account for bacterial physiology, which by extension governs both virulence factor expression and antibiotic tolerance/resistance.

Antibiotic-Induced Biofilm Formation

Surface-attached colonies of bacteria known as biofilms play a major role in the pathogenesis of device-related infections. Biofilm colonies are notorious for their resistance to suprainhibitory concentrations of antibiotics. Numerous studies have shown that subminimal inhibitory concentrations of some antibiotics can act as agonists of bacterial biofilm formation in vitro, a process that may have clinical relevance. This article reviews studies demonstrating that low-dose antibiotics induce bacterial biofilm formation. These studies have provided important information about the regulation of biofilm formation and the signaling pathways involved in global gene regulation in response to cell stressors. It is still unclear whether antibiotic-induced biofilm formation contributes to the inconsistent success of antimicrobial therapy for device infections.

Azithromycin Modulates 3',5'-cyclic Diguanylic Acid Signaling in Pseudomonas aeruginosa

Macrolides have been reported to exert a variety of effects on both host immunomodulation and repression of bacterial pathogenicity. In this study, we report that the 3',5'-cyclic diguanylic acid (c-di-GMP) signaling system, which regulates virulence in Pseudomonas aeruginosa, is affected by the macrolide azithromycin. Using DNA microarray analysis, we selected a gene encoding PA2567 related to c-di-GMP metabolism that was significantly affected by azithromycin treatment. Expression of the PA2567 gene was significantly repressed by azithromycin in a time- and dose-dependent manner, whereas no difference in PA2567 gene expression was observed in the absence of azithromycin. In-frame deletion of the PA2567 gene affected both virulence factors and the quorum-sensing system, and significantly decreased total bacteria in a mouse pneumonia model compared to the wild-type strain (P < 0.05). These results suggest that macrolides possess the ability to modulate c-di-GMP intracellular signaling in P. aeruginosa.

The Impact of a Cation Channel Blocker (Furosemide) on Pseudomonas aeruginosa PA01 Biofilm Architecture

OBJECTIVE: To determine if furosemide could have a role in inhibition of biofilm formation.

STUDY DESIGN: A prospective study of 72-hour biofilms grown in the Calgary Biofilm Device (CBD) treated with furosemide and controls.

METHODS: Bacteria were treated with furosemide and controls to determine its antiplanktonic properties. PA01 biofilms were treated with serial 2-fold dilutions of furosemide and controls over a 48-hour period at pH concentrations of 7.0, 8.0, and 9.0.

RESULTS: Furosemide had no effect on planktonic PA01. It had minimal effect at pH below 8.0. A pH of 8.0 and 9.0 reduced biofilms 25%. Furosemide 10 mg/mL reduced biofilms 50% at pH 8.0 and 9.0. It inhibited biofilms to <30% at concentrations of 0.6 to 0.16 mg/mL at pH 8.0 and <10% at concentrations of 1.25 to 0.3 mg/mL at pH 9.0.

CONCLUSION: Furosemide was found to be nonantiplanktonic, but does appear to destabilize preformed PA01 biofilms at pH-dependent concentrations.

Sub-MIC of antibiotics induced biofilm formation of Pseudomonas aeruginosa in the presence of chlorhexidine

Public health is facing a new challenge due to the alarming increase in bacterial resistance to most of the conventional antibacterial agents. It has been found that only minor cell damage is caused when exposed to sub-lethal levels of antimicrobial. Biofilms can play an important role in producing resistance, which is developed to reservoirs of pathogens in the hospital and cannot be easily removed. The aim of this study was to test whether the sub-lethal dose of antibiotics can induce biofilm formation of P. aeruginosa following incubating in the presence and absence of chlorhexidine. Standard antibiotic-micro broth 96-flat well plates were used for determination of MIC and biofilm assay. The adherence degree of biofilm was determined by estimation of OD _{630 nm} values using ELISA reader. The mean 22 isolates of P. aeruginosa growing in culture with presence and absence of chlorhexidine, could exhibited the significant (p < 0.001) proportion of adherence followed incubation in sub minimal inhibitory concentrations (Sub-MIC) of cefotaxim, amoxicillin, and azithromycin in comparison with control (antibiotic-free broth), while the sub-MIC of ciprofloxacin revealed significant inhibition of biofilm. Conclusion: Incubating the isolates of P. aeruginosa to sub-MIC of antibiotics exhibited induction of biofilm in the presence of chlorhexidine.

Antivirulence activity of azithromycin in Pseudomonas aeruginosa

Antibiotics represent our bulwark to combat bacterial infections, but the spread of antibiotic resistance compromises their clinical efficacy. Alternatives to conventional antibiotics are urgently needed in order to complement the existing antibacterial arsenal. The macrolide antibiotic azithromycin (AZM) provides a paradigmatic example of an "unconventional" antibacterial drug. Besides its growth-inhibiting activity, AZM displays potent anti-inflammatory properties, as well as antivirulence activity on some intrinsically resistant bacteria, such as Pseudomonas aeruginosa. In this bacterium, the antivirulence activity of AZM mainly relies on its ability to interact with the ribosome, resulting in direct and/or indirect repression of specific subsets of genes involved in virulence, quorum sensing, biofilm formation, and intrinsic antibiotic resistance. Both clinical experience and clinical trials have shown the efficacy of AZM in the treatment of chronic pulmonary infections caused by P. aeruginosa. The aim of this review is to combine results from laboratory studies with evidence from clinical trials in order to unify the information on the in vivo mode of action of AZM in P. aeruginosa infection.

Synergistic combination of marine oligosaccharides and azithromycin against Pseudomonas aeruginosa

In this paper we describe how utilization of low molecular weight alginate-derived oligosaccharide (ADO) and chito-oligosaccharide (COS) in conjunction with antibiotics, could more effectively inhibit the growth of wild-type and resistant Pseudomonas aeruginosa. Inhibition is effected by modulating the bacteria's quorum sensing (QS) system, thus regulating biofilm formation and reducing resistance to antibiotic treatment. This can be demonstrated by using conventional MIC screening. COS showed synergistic effects with azithromycin, whereas ADO indicated additive effects against wild-type P. aeruginosa. Using electrospray-ionization mass spectroscopy (ESI-MS), matrix-assisted laser desorption/ionization-time of flightmass spectroscopy (MALDI-TOF-MS) and nuclear magnetic resonance (NMR), the chemical structure of ADO and of COS was characterized. The wild-type and resistant strains were identified by 16S rRNA sequence analysis. This report demonstrates the feasibility of attenuating the tolerance of P. aeruginosa to azithromycin by using specific marine oligosaccharides.

State of progress in treating cystic fibrosis respiratory disease

Since the discovery of the gene associated with cystic fibrosis (CF), there has been tremendous progress in the care of patients with this disease. New therapies have entered the market and are part of the standard treatment of patients with CF, and have been associated with marked improvement in survival. Now there are even more promising therapies directed at different components of the pathophysiology of this disease. In this review, our current knowledge of the pathophysiology of lung disease in patients with CF is described, along with the current treatment of CF lung disease, and the therapies in development that offer great promise to our patients.

Effect of gingivitis on azithromycin concentrations in gingival crevicular fluid

BACKGROUND

Macrolide antibiotics yield high concentrations in inflamed tissue, suggesting that their levels in gingival crevicular fluid (GCF) could be increased at gingivitis sites. However, the increased volume of GCF associated with gingivitis could potentially dilute macrolides. To determine whether these assumptions are correct, the bioavailability of systemically administered azithromycin was compared in GCF from healthy and gingivitis sites.

METHODS

Experimental gingivitis was induced in one maxillary posterior sextant in nine healthy individuals. Contralateral healthy sextants served as controls. Participants ingested 500 mg azithromycin, followed by a 250-mg dose 24 hours later. Four hours after the second dose, plaque was removed from experimental sites. GCF was collected from eight surfaces in both the experimental and control sextants and pooled separately. GCF samples were subsequently collected on days 2, 3, 8, and 15, and azithromycin content was determined by agar diffusion bioassay.

RESULTS

On days 2 and 3, the pooled GCF volume at experimental sites was significantly higher than at control sites (P <0.01), and the total azithromycin mass in 30-second GCF samples pooled from experimental sites was significantly higher than at control sites (P <0.02). However, there were no significant differences in azithromycin concentration between the experimental and control pools at any point. Concentrations exceeded 7.3 μg/mL on day 2 and 2.5 μg/mL on day 15.

CONCLUSION

Azithromycin concentrations are similar in GCF from gingivitis sites and healthy sites, suggesting that the processes that regulate GCF azithromycin concentration can compensate for local inflammatory changes.

Synergistic effects of antibiotics and an N-acyl homoserine lactone analog on Porphyromonas gingivalis biofilms

AIMS

To investigate the effects of the combined application of an N-acyl homoserine lactone (HSL) analog and antibiotics on biofilms of Porphyromonas gingivalis, a major pathogen of periodontal disease.

METHODS AND RESULTS

Antibiotics used were cefuroxime, ofloxacin and minocycline. A flow-cell model was used for biofilm formation. Samples were divided into four groups: control, analog-treated, antibiotic-treated and combined application groups. Biofilm cell survival was determined using adenosine triphosphate (ATP) bioluminescence and confocal laser microscopy (CLSM). In the combined application group, the ATP count in biofilm cells was significantly decreased compared with the antibiotic-treated group (Games-Howell test, P < 0·05). A combination of cefuroxime and the analog was most effective against the P. gingivalis biofilm. CLSM observations revealed that the proportion of dead cells was highest in the combined application group.

CONCLUSIONS

The combined application of the N-acyl HSL analog and antibiotics was effective at reducing the viability of P. gingivalis cells in biofilms.

SIGNIFICANCE AND IMPACT OF THE STUDY

The combined application of the N-acyl HSL analog and antibiotics may be successful for eradicating infections involving bacterial biofilms, such as periodontitis.

Should multivisceral transplantation be considered in patients colonized with multidrug-resistant Pseudomonas aeruginosa?

This report describes two subsequent liver-small bowel-pancreas-kidney (multivisceral) transplantations in a child colonized with multidrug-resistant Pseudomonas aeruginosa. We discuss the dilemma concerning the transplantation of patients colonized with multidrug-resistant Pseudomonas spp., its potential consequences, and the peri and postoperative management of these patients.

Antibiofilm effects of azithromycin and erythromycin on Porphyromonas gingivalis

Antibiotic resistance of biofilm-grown bacteria contributes to chronic infections, such as marginal and periapical periodontitis, which are strongly associated with Porphyromonas gingivalis. Concurrent azithromycin (AZM) administration and mechanical debridement improve the clinical parameters of periodontal tissue in situ. We examined the in vitro efficacy of AZM against P. gingivalis biofilms. The susceptibilities of adherent P. gingivalis strains 381, HW24D1, 6/26, and W83 to AZM, erythromycin (ERY), ampicillin (AMP), ofloxacin (OFX), and gentamicin (GEN) were investigated using a static model. The optical densities of adherent P. gingivalis cells were significantly decreased by using AZM and ERY at sub-MIC levels compared with those of the controls in all the strains tested, except for the effect of ERY on strain W83. AMP and OFX inhibited P. gingivalis adherent cells at levels over their MICs, and GEN showed no inhibition in the static model. The effects of AZM and ERY against biofilm cells were investigated using a flow cell model. The ATP levels of P. gingivalis biofilms were significantly decreased by AZM at concentrations below the sub-MICs; however, ERY was not effective for inhibition of P. gingivalis biofilm cells at their sub-MICs. Furthermore, decreased density of P. gingivalis biofilms was observed three-dimensionally with sub-MIC AZM, using confocal laser scanning microscopy. These findings suggest that AZM is effective against P. gingivalis biofilms at sub-MIC levels and could have future clinical application for oral biofilm infections, such as chronic marginal and periapical periodontitis.

Azithromycin concentrations in blood and gingival crevicular fluid after systemic administration

BACKGROUND

Azithromycin is a macrolide antibiotic that is active against several periodontal pathogens. Macrolides are taken up and concentrated inside gingival fibroblasts, which could influence their pharmacokinetics. This study tests the hypothesis that steady-state levels of azithromycin are higher and more sustained in gingival crevicular fluid (GCF) than in serum.

METHODS

Four healthy patients received an initial dose of 500-mg azithromycin followed by 250-mg doses on each of the next 2 days. Serum and GCF samples were obtained 2 hours after the last dose on day 2, and on days 4 and 7. GCF samples were collected from maxillary posterior sites with paper strips. The strips were pooled and eluted with high-purity water. After extraction, the azithromycin content of the serum samples and GCF eluates was determined with an agar diffusion bioassay.

RESULTS

On days 2, 4, and 7, the concentrations of azithromycin in blood serum were 0.22 ± 0.02, 0.08 ± 0.02, and 0.04 ± 0.01 μg/mL, respectively. The concentrations in GCF were 8.82 ± 1.25, 7.90 ± 1.72, and 7.38 ± 1.15 μg/mL, respectively. Mean GCF levels were significantly higher than mean serum levels (P ≤0.02; paired t test).

CONCLUSIONS

The findings demonstrate that the pharmacokinetic profiles of azithromycin are different in GCF and serum. At steady state, azithromycin concentrations in GCF were higher and more sustained than those in serum. Based on previous studies, the levels observed in GCF were above the minimal inhibitory concentration for Aggregatibacter actinomycetemcomitans (previously Actinobacillus actinomycetemcomitans), Porphyromonas gingivalis, and Prevotella intermedia.

Azithromycin paradox in the treatment of cystic fibrosis airway disease

Evaluation of: Saiman L, Anstead M, Mayer-Hamblett N et al.: Effect of azithromycin on pulmonary function in patients with cystic fibrosis uninfected with Pseudomonas aeruginosa: a randomized controlled trial. JAMA 303(17), 1707–1715 (2010). Chronic airway infection and inflammation are hallmarks of cystic fibrosis (CF). Disease progression can be described as chronic inflammation punctuated by acute exacerbations with overt immunological responses. Macrolide antibiotics, which have both immunomodulatory and antibacterial activities, have been shown to be beneficial in the management of CF airway disease, although the mechanism of action is unknown. It is also unclear whether all patients, particularly those not colonized with Pseudomonas aeruginosa, benefit from this treatment. In this article, Saiman et al. examine the effects of azithromycin on lung function in pediatric and adolescent CF patients who are not colonized with P. aeruginosa. The data indicate beneficial effects of azithromycin treatment and suggest the mechanisms of action of azithromycin is at least partially independent of P. aeruginosa.

Effects of subminimum inhibitory concentrations of antibiotics on the Pasteurella multocida proteome: a systems approach

To identify key regulators of subminimum inhibitory concentration (sub-MIC) antibiotic response in the Pasteurella multocida proteome, we applied systems approaches. Using 2D-LC-ESI-MS², we achieved 53% proteome coverage. To study the differential protein expression in response to sub-MIC antibiotics in the context of protein interaction networks, we inferred P. multocida Pm70 protein interaction network from orthologous proteins. We then overlaid the differential protein expression data onto the P. multocida protein interaction network to study the bacterial response. We identified proteins that could enhance antimicrobial activity. Overall compensatory response to antibiotics was characterized by altered expression of proteins involved in purine metabolism, stress response, and cell envelope permeability.

Effects of prolonged use of azithromycin in patients with cystic fibrosis: a meta-analysis

Azithromycin has been studied as potential therapeutic anti-inflammatory agent for cystic fibrosis (CF) patients. Azithromycin (AZM) has been used as an immunomodulating agent, based on few small studies. Considering the cost and potential side effects of long-term azithromycin therapy, it is important to identify the group of patients that would benefit the most. Weighted mean difference was used for pulmonary function tests, and risk ratios for all other variables. The random-effects model was applied for all reports. Combining four studies (N=368), azithromycin showed increase in FEV(1) (3.53%, 95% CI 0.00, 7.07, p=0.05; I(2)=38%) and FVC (4.24%, 95% CI 2.02, 6.45, p=0.0002; I(2)=0%). When trials were analyzed by baseline Pseudomonas sputum colonization, the heterogeneity decreased (I(2)=0%), FEV(1) significantly increased to 4.66% (95% CI 1.18, 8.15, p=0.009), and FVC increased to 4.64% (95% CI 2.11, 7.17, p=0.0003). The GI side effects were 72% higher with azithromycin use (RR 1.72, 95% CI 1.33, 2.21, p=0.00003), the main side effects being nausea (RR 2.04, 95% CI 1.19, 3.45, p=0.009), and diarrhea (RR 2.12, 95% CI 1.10, 4.08, p=0.02). Azithromycin improves lung function of CF patients, especially in the subgroup colonized with Pseudomonas. However, nausea and diarrhea are significantly more frequent with azythromycin.

Anti-inflammatory therapies for cystic fibrosis-related lung disease

Cystic fibrosis (CF) is an autosomal recessive disease affecting many organ systems. In the lung, the underlying ion transport defect in CF establishes a perpetuating cycle of impaired airway clearance, chronic endobronchial infection, and exuberant inflammation. The interrelated nature of these components of CF lung disease makes it likely that the most effective therapeutic strategies will include treatments of each of these. This chapter reviews the preclinical and clinical data focused on ways to better understand and particularly to limit inflammation in the CF airway. Anti-inflammatories are an attractive therapeutic target in CF with a proven ability to decrease the rate of decline in lung function. However, the inherent complexity of the inflammatory response combined with the obvious dependency on this response to contain infection and the side effect profiles of common anti-inflammatories have made identifying the most suitable agents challenging. Research continues to discover impairments in signaling events in CF that may contribute to the excessive inflammation seen clinically. Concurrent with these findings, promising new therapies are being evaluated to determine which agents will be most effective and well tolerated. Available data from studies commenced over the last two decades, which have generated both encouraging and disappointing results, are reviewed below.

Once-weekly azithromycin in cystic fibrosis with chronic Pseudomonas aeruginosa infection

BACKGROUND

Data on the effects of long-term treatment with azithromycin (AZM) on inflammatory markers in cystic fibrosis patients chronically infected with Pseudomonas aeruginosa are scarce. So far there is no pharmacokinetic and clinical data on once-weekly dosage of AZM in CF patients.

METHODS

In a randomised double-blind, placebo-controlled trial, patients received AZM or placebo 1 per week for 8 weeks (AZM dosage--20-29 kg: 500 mg, 30-39 kg: 750 mg, 40-49 kg: 1000 mg and > or = 50 kg: 1250 mg) after a course of intravenous antipseudomonal antibiotics. Pulmonary function tests, the serum markers LPS-binding protein (LBP), interleukin-8 (IL-8), CRP, P. aeruginosa alginate in sputum samples and quality of life scores were evaluated.

RESULTS

Thirty-eight patients (21 AZM/17 placebo) (mean age: 23.7 years; mean FEV(1): 62% of predicted) were recruited. After treatment (mean dose of 21.2 mg/kg body weight once a week) pulmonary function declined in both groups compared to baseline (i.e. after cessation of i.v. antibiotics). The AZM group was significantly better for mean changes in serum CRP (AZM: +0.9 mg/l, placebo: +21.6 mg/l, p=0.019), lipopolysaccharide binding protein in serum, LBP (AZM: +0.9 microg/ml, placebo: +7.0 microg/ml, p=0.015), serum interleukin-8 (AZM: -3.1 pg/ml, placebo: +2.9 pg/ml, p=0.001) and alginate in sputum (AZM: +85 microg/ml, placebo: +353 microg/ml, p=0.048). Quality of life was significantly better after AZM and there was no increase in treatment-related adverse events.

CONCLUSION

Once-weekly azithromycin ameliorated inflammatory reactions and improved quality of life. A decline of pulmonary function after cessation of i.v. antibiotics could not be prevented.

What's new in cystic fibrosis? From treating symptoms to correction of the basic defect

Chronic relentless lung infection and pancreatic insufficiency are the cardinal features of cystic fibrosis (CF), a life-shortening autosomal recessive disease. Mutations in the 'cystic fibrosis transmembrane conductance regulator' (CFTR) are currently classified into five groups according to their repercussion on CFTR protein synthesis and its chloride channel function. Stop codon mutations (class I) result in a truncated nonfunctional CFTR, class II mutations consist of aberrantly folded CFTR protein that is degraded by the cell quality control system, while class III mutations lead to defective regulation of the CFTR protein and, consequently, the absence of CFTR function. These three classes usually lead to a classic CF phenotype with pancreatic insufficiency. CFTR mutations that lead to defective chloride conductance are grouped together in class IV. Class V mutations interfere with normal transcription, thereby reducing the amount of otherwise normal CFTR. These latter two classes are mostly associated with a milder expression of the disease. In the absence of CFTR function, unrestrained Na+ absorption and the failure of active Cl- secretion lead to a decreased airway surface liquid (ASL) volume and subsequent failure of normal mucociliary clearance. This review highlights recent therapeutic strategies that either target the underlying defect or the early steps in CF pathophysiology. To date, gene therapy has failed to demonstrate a clinical benefit after repeated administration. Mutation-specific chloride channel correction pharmacotherapy is currently being developed, an example of which is PTC124, a new chemical compound that selectively induces read-through of premature stop codons. However, clinical efficacy for most of the compounds still has to be proven in large clinical trials. The positive effect of nebulised hypertonic saline on mucociliary clearance is based on the restoration of ASL height. Recent advances in the current treatment of lung infection and inflammation are highlighted in this review. Lung transplantation should be considered in terminally ill patients, but the timing of the transplantation is crucial: transplanting too early shortens survival, while transplanting too late results in patients dying on the waiting list.

Effects of ambroxol on alginate of mature Pseudomonas aeruginosa biofilms

Biofilm-forming bacteria Pseudomonas aeruginosa is a common pathogen in mechanically ventilated newborns, which can cause life-threatening infections. Alginate of mucoid Pseudomonas aeruginosa biofilms is considered an important virulence factor which contributes to the resistance to antibiotics. Traditionally, ambroxol is widely used in newborns with lung problems as a mucolytic agent and antioxidant agent as well. And there are few studies that demonstrated the anti-biofilm activity of ambroxol. In this study, we found that ambroxol can affect the structure of mucoid Pseudomonas aeruginosa biofilms. Further, we found that ambroxol reduces the production of alginate, the expression of the important genes and the activity of key enzyme guanosine diphospho-D-mannose dehydrogenase (GDP-mannose dehydrogenase; GMD) which were involved in alginate biosynthesis.

Inflammation and anti-inflammatory therapies for cystic fibrosis

Cystic fibrosis lung disease is characterized by a self-propagating cycle of obstruction, infection, and inflammation. The inflammatory response, which accounts for the majority of the morbidity and mortality of the disease, begins early in life, becomes persistent, and is excessive relative to the bacterial burden. Therapies aimed at decreasing the inflammatory response represent a relatively new strategy for treatment. This article reviews the current state of the art of anti-inflammatory therapy in cystic fibrosis and introduces clinical trials that are underway.

Azithromycin blocks quorum sensing and alginate polymer formation and increases the sensitivity to serum and stationary-growth-phase killing of Pseudomonas aeruginosa and attenuates chronic P. aeruginosa lung infection in Cftr(-/-) mice

The consequences of O-acetylated alginate-producing Pseudomonas aeruginosa biofilms in the lungs of chronically infected cystic fibrosis (CF) patients are tolerance to both antibiotic treatments and effects on the innate and the adaptive defense mechanisms. In clinical trials, azithromycin (AZM) has been shown to improve the lung function of CF patients. The present study was conducted in accordance with previous in vitro studies suggesting that the effect of AZM may be the inhibition of alginate production, blockage of quorum sensing (QS), and increased sensitivity to hydrogen peroxide and the complement system. Moreover, we show that AZM may affect the polymerization of P. aeruginosa alginate by the incomplete precipitation of polymerized alginate and high levels of readily dialyzable uronic acids. In addition, we find that mucoid bacteria in the stationary growth phase became sensitive to AZM, whereas cells in the exponential phase did not. Interestingly, AZM-treated P. aeruginosa lasI mutants appeared to be particularly resistant to serum, whereas bacteria with a functional QS system did not. We show in a CF mouse model of chronic P. aeruginosa lung infection that AZM treatment results in the suppression of QS-regulated virulence factors, significantly improves the clearance of P. aeruginosa alginate biofilms, and reduces the severity of the lung pathology compared to that in control mice. We conclude that AZM attenuates the virulence of P. aeruginosa, impairs its ability to form fully polymerized alginate biofilms, and increases its sensitivity to complement and stationary-phase killing, which may explain the clinical efficacy of AZM.

Quorum-sensing antagonistic activities of azithromycin in Pseudomonas aeruginosa PAO1: a global approach

The administration of macrolides such as azithromycin for chronic pulmonary infection of cystic fibrosis patients has been reported to be of benefit. Although the mechanisms of action remain obscure, anti-inflammatory effects as well as interference of the macrolide with Pseudomonas aeruginosa virulence factor production have been suggested to contribute to an improved clinical outcome. In this study we used a systematic approach and analyzed the impact of azithromycin on the global transcriptional pattern and the protein expression profile of P. aeruginosa PAO1 cultures versus those in untreated controls. The most remarkable result of this study is the finding that azithromycin exhibited extensive quorum-sensing antagonistic activities. In accordance with the inhibition of the quorum-sensing systems, virulence factor production was diminished and the oxidative stress response was impaired, whereas the type III secretion system was strongly induced. Moreover, P. aeruginosa motility was reduced, which probably accounts for the previously observed impaired biofilm formation capabilities of azithromycin-treated cultures. The interference of azithromycin with quorum-sensing-dependent virulence factor production, biofilm formation, and oxidative stress resistance in P. aeruginosa holds great promise for macrolide therapy in cystic fibrosis. Clearly quorum-sensing antagonist macrolides should be paid more attention in the management of chronic P. aeruginosa infections, and as quorum-sensing antagonists, macrolides might gain vital importance for more general application against chronic infections.

Allograft Rejection After Lung Transplantation

Lung transplantation has become an accepted therapy for selected patients with advanced lung disease. One of the main limitations to successful lung transplantation is rejection of the transplanted organ. This article discusses the clinical presentation, treatment, and prevention of hyperacute, acute, and chronic rejection in the lung transplant recipient.

Airway biofilms: implications for pathogenesis and therapy of respiratory tract infections

The differentiation of bacterial biofilms in the airway environment, the pathogenesis of airway biofilm, and possible therapeutic methods are discussed. Biofilm diseases that characteristically involve the respiratory system include cystic fibrosis (CF), diffuse panbronchiolitis (DPB), and bronchiectasia with Pseudomonas aeruginosa (P. aeruginosa) infection. There is evidence to suggest that almost all strains of P. aeruginosa have the genetic capacity to synthesize alginate, a main matrix of biofilms, when ecological conditions are unfavorable for their survival. The bacteria inside the mature biofilm show increased resistance to both antibacterials and phagocytic cells, express fewer virulence factors because of their stationary state of growth, and are less stimulatory to the mucosa because of the 'sandwich binding'. These factors facilitate both the colonization of bacteria and their extended survival even under unfavorable conditions. Since the biofilm limits colonization to a latent form, the clinical symptoms in this situation are unremarkable. However, the clinical progression of both CF and DPB proceeds in two characteristic directions. The first is an acute exacerbation caused by planktonic bacteria that have germinated from the biofilm. The second is a slow progression of disease that is induced by harmful immune reactions. The harmful reactions are mediated by alginate, which induces antigen antibody reactions around the airways, as well as formation of circulating immune complexes that are deposited on lung tissue. Furthermore, the highest titer of bacterial permeability increasing anti-neutrophil cytoplasmic autoantibodies (BPI-ANCA) is observed in association with highly impaired pulmonary function in patients with CF and DPB, as well as in patients with a lengthy period of colonization with P. aeruginosa. BPI-ANCA subsequently makes chronic airway infection even more intractable. The long-term use of 14- or 15-ring membered macrolides results in a favorable clinical outcome for patients with DPB and in some patients with CF. In the last 10 years, an increasing number of studies have reported secondary actions of macrolides that include effects on both airway and phagocytic cells, as well as an anti-biofilm activity. The 14- or 15-ring membered macrolides inhibit: (i) the alginate production from P. aeruginosa; (ii) the antibody reaction to alginate, which leads to a decrease in the immune complex formation; and (iii) the activation of the autoinducer 3-O-C12-homoserine lactone and subsequent expression of lasI and rhlI in quorum sensing systems in P. aeruginosa. These anti-biofilm actions of macrolides may represent their basic mechanisms of action on airway biofilm disease.

Long-Term Azithromycin Use for Treatment of Bronchiolitis Obliterans Syndrome in Lung Transplant Recipients

Short-term improvement in lung function was observed in 5 of 6 lung transplant recipients with bronchiolitis obliterans syndrome (BOS) who were treated with oral azithromycin. We assessed the long-term effect (mean duration 10 months) of treatment with oral azithromycin in 11 lung transplant recipients with BOS. Mean forced expiratory volume in 1 second (FEV1) was 40 +/- 9% at initiation of azithromycin treatment, 39 +/- 10% after 1 month, 39 +/- 12% after 4 months, 38 +/- 10% after 7 months and 38 +/- 10% after 10 months, respectively (statistically non-significant for all data). We conclude that long-term administration with oral azithromycin does not reverse BOS in lung transplant recipients, but may slow progression of the disease.

Macrolides and airway inflammation in children

For more than 20 years macrolide antibiotics have been used to treat chronic inflammatory airway diseases based on their immunomodulatory activity. Macrolide antibiotics down-regulate damaging prolonged inflammation as well as increase mucus clearance, decrease bacterial virulence and prevent biofilm formation. Initially shown to decrease morbidity and mortality in diffuse panbronchiolitis and in steroid-dependent asthma, long-term macrolide therapy has now been shown to significantly reduce exacerbations and improve lung function and quality of life in children with cystic fibrosis. They have also proven beneficial in Japanese children and adults with chronic sinobronchitis especially when there is nasal polyposis. Long-term macrolides have also proven clinically beneficial in some patients with plastic bronchitis. Adverse reactions are few and generally self-limited when used at the recommended dosage for immunomodulation.

Maintenance azithromycin therapy for bronchiolitis obliterans syndrome: results of a pilot study

Bronchiolitis obliterans syndrome remains the leading cause of morbidity and mortality in the pulmonary transplant population. Previous studies show that macrolide antibiotics may be efficacious in the treatment of panbronchiolitis and cystic fibrosis. In the latter, azithromycin decreases the number of respiratory exacerbations, improves FEV1, and improves quality of life. We hypothesized that oral azithromycin therapy may improve lung function in patients with bronchiolitis obliterans syndrome. To test this hypothesis, we conducted an open-label pilot trial using maintenance azithromycin therapy in six lung transplant recipients (250 mg orally three times per week for a mean of 13.7 weeks). In this study, five of these six individuals demonstrated significant improvement in pulmonary function, as assessed by FEV1, as compared with their baseline values at the start of azithromycin therapy. The mean increase in the percentage of predicted FEV1 values in these individuals was 17.1% (p </= 0.05). In addition, the absolute FEV1 increased by 0.50 L (range -0.18 to 1.36 L). These data suggest a potential role for maintenance macrolide therapy in the treatment of bronchiolitis obliterans syndrome in lung transplant recipients.

Effect of subminimal inhibitory concentrations of azithromycin on adherence of Pseudomonas aeruginosa to polystyrene

Pseudomonas aeruginosa forms a bacterial biofilm by producing alginate when it adheres to mucosa or various medical devices. In this study, the effect of subminimal inhibitory concentrations (subMICs) of azithromycin (AZM) on the biofilm formation and in vitro adherence to polystyrene of 14 wild-type P. aeruginosa strains was studied. A total of 35 P. aeruginosa isolates from clinical specimens were used. Glycocalyx production was determined by the tube method, and bacterial adherence to the wells of flat bottom polystyrene tissue culture plates was estimated by the spectrophotometric method. Compared to the control, the adherence ability to polystyrene was inhibited by incubation with subMICs of AZM in a dose-dependent manner. These results support the findings of other investigators suggesting that AZM in subinhibitory concentrations may be useful in the prevention or treatment of biofilm-associated infections due to P. aeruginosa.

Influence of macrolides on guanosine diphospho-D-mannose dehydrogenase activity in Pseudomonas biofilm

The formation of biofilm is regarded as a major cause of intractable infectious disease. Our studies were done to elucidate the action of a 14-membered-ring macrolide (erythromycin; EM) and a 16-membered-ring macrolide (midecamycin; MDM) on guanosine diphospho-d-mannose dehydrogenase (GDP-mannose dehydrogenase; GMD), one of the constituents of bacterial biofilm that is known to produce alginate. The mucoid type of Pseudomonas aeruginosa PT-1578 and the non-mucoid type of P. aeruginosa PAO1 were grown with nutrient-rich and nutrient-poor media. Comparative measurements were made of their GMD enzyme activities, with glucose-6-phosphate dehydrogenase (G6PDH), a cell membrane enzyme, used as a control. It was found that the GMD enzyme activity of mucoid type of Pseudomonas bacteria increased when they were grown on nutrient-poor media. Measurements were also made to determine the effects of EM and MDM against GMD and G6PDH enzyme activities. In media with either EM or MDM added, the production of G6PDH was not inhibited, irrespective of the concentration of EM or MDM. However, EM was effective against the production of GMD, showing a concentration-dependent effect. Scanning electron microscopy studies were also carried out to determine the effects of both macrolides on bacterial alginate production. It was found that reduction of alginate content occurred after the addition of EM. When environmental conditions for bacteria deteriorate, GMD enzyme is activated, production of alginate is initiated, and then biofilm is formed. Our results suggest that EM may have an inhibitory effect on the GMD production cycle, hence inhibiting the formation of biofilm. This may explain the differences in the clinical usefulness of 14-membered-and 16-membered-ring macrolides against biofilm disease.