Effects of azithromycin on clinical isolates of Pseudomonas aeruginosa from cystic fibrosis patients

Practical Guidance for Clinical Microbiology Laboratories: Updated guidance for processing respiratory tract samples from people with cystic fibrosis

SUMMARYThis guidance presents recommendations for clinical microbiology laboratories for processing respiratory samples from people with cystic fibrosis (pwCF). Appropriate processing of respiratory samples is crucial to detect bacterial and fungal pathogens, guide treatment, monitor the epidemiology of cystic fibrosis (CF) pathogens, and assess therapeutic interventions. Thanks to CF transmembrane conductance regulator modulator therapy, the health of pwCF has improved, but as a result, fewer pwCF spontaneously expectorate sputum. Thus, the collection of sputum samples has decreased, while the collection of other types of respiratory samples such as oropharyngeal and bronchoalveolar lavage samples has increased. To optimize the detection of microorganisms, including Pseudomonas aeruginosa, Staphylococcus aureus, Haemophilus influenzae, and Burkholderia cepacia complex; other less common non-lactose fermenting Gram-negative bacilli, e.g., Stenotrophomonas maltophilia, Inquilinus, Achromobacter, Ralstonia, and Pandoraea species; and yeasts and filamentous fungi, non-selective and selective culture media are recommended for all types of respiratory samples, including samples obtained from pwCF after lung transplantation. There are no consensus recommendations for laboratory practices to detect, characterize, and report small colony variants (SCVs) of S. aureus, although studies are ongoing to address the potential clinical impact of SCVs. Accurate identification of less common Gram-negative bacilli, e.g., S. maltophilia, Inquilinus, Achromobacter, Ralstonia, and Pandoraea species, as well as yeasts and filamentous fungi, is recommended to understand their epidemiology and clinical importance in pwCF. However, conventional biochemical tests and automated platforms may not accurately identify CF pathogens. MALDI-TOF MS provides excellent genus-level identification, but databases may lack representation of CF pathogens to the species-level. Thus, DNA sequence analysis should be routinely available to laboratories for selected clinical circumstances. Antimicrobial susceptibility testing (AST) is not recommended for every routine surveillance culture obtained from pwCF, although selective AST may be helpful, e.g., for unusual pathogens or exacerbations unresponsive to initial therapy. While this guidance reflects current care paradigms for pwCF, recommendations will continue to evolve as CF research expands the evidence base for laboratory practices.

Effects of quorum sensing-interfering agents, including macrolides and furanone C-30, and an efflux pump inhibitor on nitrosative stress sensitivity in Pseudomonas aeruginosa

Long-term administration of certain macrolides is efficacious in patients with persistent pulmonary Pseudomonas aeruginosa infection, despite how limited the clinically achievable concentrations are, being far below their MICs. An increase in the sub-MIC of macrolide exposure-dependent sensitivity to nitrosative stress is a typical characteristic of P. aeruginosa. However, a few P. aeruginosa clinical isolates do not respond to sub-MIC of macrolide treatment. Therefore, we examined the effects of sub-MIC of erythromycin (EM) on the sensitivity to nitrosative stress together with an efflux pump inhibitor (EPI) phenylalanine arginyl β-naphthylamide (PAβN). The sensitivity to nitrosative stress increased, suggesting that the efflux pump was involved in inhibiting the sub-MIC of macrolide effect. Analysis using efflux pump-mutant P. aeruginosa revealed that MexAB-OprM, MexXY-OprM, and MexCD-OprJ are factors in reducing the sub-MIC of macrolide effect. Since macrolides interfere with quorum sensing (QS), we demonstrated that the QS-interfering agent furanone C-30 (C-30) producing greater sensitivity to nitric oxide (NO) stress than EM. The effect of C-30 was decreased by overproduction of MexAB-OprM. To investigate whether the increase in the QS-interfering agent exposure-dependent sensitivity to nitrosative stress is characteristic of P. aeruginosa clinical isolates, we examined the viability of P. aeruginosa treated with NO. Although treatment with EM could reduce cell viability, a high variability in EM effects was observed. Conversely, C-30 was highly effective at reducing cell viability. Treatment with both C-30 and PAβN was sufficiently effective against the remaining isolates. Therefore, the combination of a QS-interfering agent and an EPI could be effective in treating P. aeruginosa infections.

Spiramycin Disarms Pseudomonas aeruginosa without Inhibiting Growth

Spiramycin is a 16-membered macrolide antibiotic currently used in therapy to treat infections caused by Gram-positive bacteria responsible for respiratory tract infections, and it is also effective against some Gram-negative bacteria and against Toxoplasma spp. In contrast, Pseudomonas aeruginosa, which is one of the pathogens of most concern globally, is intrinsically resistant to spiramycin. In this study we show that spiramycin inhibits the expression of virulence determinants in P. aeruginosa in the absence of any significant effect on bacterial multiplication. In vitro experiments demonstrated that production of pyoverdine and pyocyanin by an environmental strain of P. aeruginosa was markedly reduced in the presence of spiramycin, as were biofilm formation, swarming motility, and rhamnolipid production. Moreover, treatment of P. aeruginosa with spiramycin sensitized the bacterium to H2O2 exposure. The ability of spiramycin to dampen the virulence of the P. aeruginosa strain was confirmed in a Galleria mellonella animal model. The results demonstrated that when G. mellonella larvae were infected with P. aeruginosa, the mortality after 24 h was >90%. In contrast, when the spiramycin was injected together with the bacterium, the mortality dropped to about 50%. Furthermore, marked reduction in transcript levels of the antimicrobial peptides gallerimycin, gloverin and moricin, and lysozyme was found in G. mellonella larvae infected with P. aeruginosa and treated with spiramycin, compared to the larvae infected without spiramycin treatment suggesting an immunomodulatory activity of spiramycin. These results lay the foundation for clinical studies to investigate the possibility of using the spiramycin as an anti-virulence and anti-inflammatory drug for a more effective treatment of P. aeruginosa infections, in combination with other antibiotics.

Azithromycin Exhibits Activity Against Pseudomonas aeruginosa in Chronic Rat Lung Infection Model

Pseudomonas aeruginosa forms biofilms in the lungs of chronically infected cystic fibrosis patients, which are tolerant to both the treatment of antibiotics and the host immune system. Normally, antibiotics are less effective against bacteria growing in biofilms; azithromycin has shown a potent efficacy in cystic fibrosis patients chronically infected with P. aeruginosa and improved their lung function. The present study was conducted to evaluate the effect of azithromycin on P. aeruginosa biofilm. We show that azithromycin exhibited a potent activity against P. aeruginosa biofilm, and microscopic observation revealed that azithromycin substantially inhibited the formation of solid surface biofilms. Interestingly, we observed that azithromycin restricted P. aeruginosa biofilm formation by inhibiting the expression of pel genes, which has been previously shown to play an essential role in bacterial attachment to solid-surface biofilm. In a rat model of chronic P. aeruginosa lung infection, we show that azithromycin treatment resulted in the suppression of quorum sensing-regulated virulence factors, significantly improving the clearance of P. aeruginosa biofilms compared to that in the placebo control. We conclude that azithromycin attenuates P. aeruginosa biofilm formation, impairs its ability to produce extracellular biofilm matrix, and increases its sensitivity to the immune system, which may explain the clinical efficacy of azithromycin in cystic fibrosis patients.

Effect of azithromycin and phenylalanine-arginine beta-naphthylamide on quorum sensing and virulence factors in clinical isolates of Pseudomonas aeruginosa

Background and Objectives

Pseudomonas aeruginosa is a problematic opportunistic pathogen causing several types of nosocomial infections with a high resistance rate to antibiotics. Production of many virulence factors in P. aeruginosa is regulated by quorum sensing (QS), a cell-to-cell communication mechanism. In this study, we aimed to assess and compare the inhibitory effect of azithromycin (AZM) and EPI-PAβN (efflux pump inhibitor-Phenylalanine-Arginine Beta-Naphthylamide) on QS system and QS-dependent virulence factors in P. aeruginosa clinical isolates.

Materials and Methods

A total of 50 P. aeruginosa isolates were obtained from different types of clinical specimens. Isolates were investigated for detection of QS system molecules by AHL cross-feeding bioassay and QS-dependent virulence factors; this was also confirmed by detection of QS genes (lasR, lasI, rhlR, and rhlI) using PCR assay. The inhibitory effect of sub-MIC AZM and EPI PAβN on these virulence factors was assessed.

Results

All the P. aeruginosa, producing QS signals C₄HSL, failed to produce C₄HSL in the presence of sub-MIC AZM, In the presence of EPI PAβN (20 μg/ml) only 14 isolates were affected, there was a significant reduction in QS-dependent virulence factors production (protease, biofilm, rhamnolipid and pyocyanin) in the presence of either 20 μg/ml EPI or sub-MIC of AZM with the inhibitory effect of AZM was more observed than PAβN.

Conclusion

Anti-QS agents like AZM and EPI (PAβN) are useful therapeutic options for P. aeruginosa due to its inhibitory effect on QS-dependent virulence factors production without selective pressure on bacteria growth, so resistance to these agents is less likely to develop.

Structure-activity relationships of furanones, dihydropyrrolones and thiophenones as potential quorum sensing inhibitors

Since their initial isolation from the marine alga Delisea pulchra, bromofuranones have been investigated as potential inhibitors of quorum sensing (QS) in various bacterial strains. QS is an important mechanism by which bacteria co-ordinate their molecular response to the environment. QS is intrinsically linked to bacterial antibiotic resistance. Inspired by nature, chemists have developed a wide variety of synthetic analogs in an effort to elucidate the structure-activity relationships of these compounds, and to ultimately develop novel antimicrobial agents. In this work, we describe advances in this field while paying particular attention to apparent structure-activity relationships. This review is organized according to the main ring systems under investigation, namely furanones, dihydropyrrolones and thiophenones.

Achromobacter Infections and Treatment Options

Achromobacter is a genus of nonfermenting Gram-negative bacteria under order Burkholderiales Although primarily isolated from respiratory tract of people with cystic fibrosis, Achromobacter spp. can cause a broad range of infections in hosts with other underlying conditions. Their rare occurrence and ever-changing taxonomy hinder defining their clinical features, risk factors for acquisition and adverse outcomes, and optimal treatment. Achromobacter spp. are intrinsically resistant to several antibiotics (e.g., most cephalosporins, aztreonam, and aminoglycosides), and are increasingly acquiring resistance to carbapenems. Carbapenem resistance is mainly caused by multidrug efflux pumps and metallo-β-lactamases, which are not expected to be overcome by new β-lactamase inhibitors. Among the other new antibiotics, cefiderocol, and eravacycline were used as salvage therapy for a limited number of patients with Achromobacter infections. In this article, we aim to give an overview of the antimicrobial resistance in Achromobacter species, highlighting the possible place of new antibiotics in their treatment.

Reconciling Antimicrobial Susceptibility Testing and Clinical Response in Antimicrobial Treatment of Chronic Cystic Fibrosis Lung Infections

Median cystic fibrosis (CF) survival has increased dramatically over time due to several factors, including greater availability and use of antimicrobial therapies. During the progression of CF lung disease, however, the emergence of multidrug antimicrobial resistance can limit treatment effectiveness, threatening patient longevity. Current planktonic-based antimicrobial susceptibility testing lacks the ability to predict clinical response to antimicrobial treatment of chronic CF lung infections. There are numerous reasons for these limitations including bacterial phenotypic and genotypic diversity, polymicrobial interactions, and impaired antibiotic efficacy within the CF lung environment. The parallels to other chronic diseases such as non-CF bronchiectasis are discussed as well as research priorities for moving forward.

Standard versus biofilm antimicrobial susceptibility testing to guide antibiotic therapy in cystic fibrosis

BACKGROUND

Clinicians typically select the antibiotics used to treat pulmonary infections in people with cystic fibrosis based on the results of antimicrobial susceptibility testing performed on bacteria traditionally grown in a planktonic mode (grown in a liquid). However, there is considerable evidence to suggest that Pseudomonas aeruginosa actually grows in a biofilm (or slime layer) in the airways of people with cystic fibrosis with chronic pulmonary infections. Therefore, choosing antibiotics based on biofilm rather than conventional antimicrobial susceptibility testing could potentially improve response to treatment of Pseudomonas aeruginosa in people with cystic fibrosis. This is an update of a previously published Cochrane Review.

OBJECTIVES

To compare biofilm antimicrobial susceptibility testing-driven therapy to conventional antimicrobial susceptibility testing-driven therapy in the treatment of Pseudomonas aeruginosa infection in people with cystic fibrosis.

SEARCH METHODS

We searched the Cochrane Cystic Fibrosis Trials Register, compiled from electronic database searches and handsearching of journals and conference abstract books. Most recent search: 07 April 2020. We also searched two ongoing trials registries and the reference lists of relevant articles and reviews. Most recent searches: 07 April 2020 and 05 September 2017.

SELECTION CRITERIA

Randomized controlled trials (RCTs) of antibiotic therapy based on biofilm antimicrobial susceptibility testing compared to antibiotic therapy based on conventional antimicrobial susceptibility testing in the treatment of Pseudomonas aeruginosa pulmonary infection in people with cystic fibrosis.

DATA COLLECTION AND ANALYSIS

Two authors independently selected RCTs, assessed their risk of bias and extracted data from eligible trials. Additionally, the review authors contacted the trial investigators to obtain further information. The quality of the evidence was assessed using the GRADE criteria.

MAIN RESULTS

The searches identified two multicentre, double-blind RCTs eligible for inclusion in the review with a total of 78 participants (adults and children); one RCT was undertaken in people who were clinically stable, the second was in people experiencing pulmonary exacerbations. Both RCTs prospectively assessed whether the use of biofilm antimicrobial susceptibility testing improved microbiological and clinical outcomes in participants with cystic fibrosis who were infected with Pseudomonas aeruginosa. The primary outcome was the change in sputum Pseudomonas aeruginosa density from the beginning to the end of antibiotic therapy. Although the intervention was shown to be safe, the data from these two RCTs did not provide evidence that biofilm susceptibility testing was superior to conventional susceptibility testing either in terms of microbiological or lung function outcomes. One of the trials also measured risk and time to subsequent exacerbation as well as quality of life measures and did not demonstrate any difference between groups in these outcomes. Both RCTs had an overall low risk of bias and the quality of the evidence using GRADE criteria was deemed to be moderate to high for the outcomes selected.

AUTHORS' CONCLUSIONS

The current evidence is insufficient to recommend choosing antibiotics based on biofilm antimicrobial susceptibility testing rather than conventional antimicrobial susceptibility testing in the treatment of Pseudomonas aeruginosa pulmonary infections in people with cystic fibrosis. Biofilm antimicrobial susceptibility testing may be more appropriate in the development of newer, more effective formulations of drugs which can then be tested in clinical trials.

Effects of a sub-minimum inhibitory concentration of chlorhexidine gluconate on the development of in vitro multi-species biofilms

Following antimicrobial administrations in oral environments, bacteria become exposed to a sub-minimum inhibitory concentration (sub-MIC), which can induce in vitro single-species biofilms. This study explored the effects of chlorhexidine gluconate (CHG) at a sub-MIC on in vitro multi-species biofilms comprising Streptococcus mutans, Streptococcus oralis and Actinomyces naeslundii. CHG at a sub-MIC was found to induce in vitro biofilm growth, although the bacterial growth was not significantly different from that in the control. The gene transcription related to S. mutans multi-species biofilm formation with CHG at a sub-MIC was significantly higher than that of the control, but this was not found in S. mutans single-species biofilms. The bio-volume of extracellular polysaccharides with CHG at a sub-MIC was significantly higher than that of the control. This suggests that CHG at a sub-MIC may promote the development of multi-species biofilms by affecting the gene transcription related to S. mutans biofilm formation.

Sub-MIC effects of a proline-rich antibacterial peptide on clinical isolates of Acinetobacter baumannii

INTRODUCTION

Acinetobacter baumannii is one of the most important nosocomial pathogens, mainly due to its ability to accumulate antibiotic-resistances and to persist in the hospital environment - characteristics related to biofilm production. It is well-known that A. baumannii is inhibited by the proline-rich peptide Bac7(1-35), but its putative effects at sub-MICs were never considered.

AIMS

We examined the sub-MIC effect of Bac7(1-35) on the growth rate, resistance induction and some A. baumannii features linked to virulence.

METHODOLOGY

Growth kinetics in the presence of sub-MICs of Bac7(1-35) were evaluated spectrophotometrically. Peptide uptake was quantified by cytometric analysis. The ability of Bac7(1-35) to interfere with biofilm production was investigated by the crystal violet method and confocal microscopy. Bacterial motility was observed at the interphase between a layer of a semi-solid medium and the polystyrene bottom of a Petri dish. The induction of resistance was evaluated after serial passages with sub-MICs of the peptide.

RESULTS

Although the MIC of Bac7(1-35) was between 2-4 µM for all tested strains, its effect on the growth rate at sub-MICs was strain-dependent and correlated with the amount of peptide internalized by each strain. Sub-MICs of Bac7(1-35) induced a strongly strain-dependent effect on biofilm formation and reduced motility in almost all strains, but interestingly the peptide did not induce resistance.

CONCLUSION

Bac7(1-35) is internalized into A. baumannii and is able to inhibit biofilm formation and bacterial motility, without inducing resistance. This study stresses the importance of considering possible effects that antimicrobials could have at sub-MICs, mimicking a common condition during antibiotic treatment.

A permeability-increasing drug synergizes with bacterial efflux pump inhibitors and restores susceptibility to antibiotics in multi-drug resistant Pseudomonas aeruginosa strains

Resistance to antibiotics poses a major global threat according to the World Health Organization. Restoring the activity of existing drugs is an attractive alternative to address this challenge. One of the most efficient mechanisms of bacterial resistance involves the expression of efflux pump systems capable of expelling antibiotics from the cell. Although there are efflux pump inhibitors (EPIs) available, these molecules are toxic for humans. We hypothesized that permeability-increasing antimicrobial peptides (AMPs) could lower the amount of EPI necessary to sensitize bacteria to antibiotics that are efflux substrates. To test this hypothesis, we measured the ability of polymyxin B nonapeptide (PMBN), to synergize with antibiotics in the presence of EPIs. Assays were performed using planktonic and biofilm-forming cells of Pseudomonas aeruginosa strains overexpressing the MexAB-OprM efflux system. Synergy between PMBN and EPIs boosted azithromycin activity by a factor of 2,133 and sensitized P. aeruginosa to all tested antibiotics. This reduced several orders of magnitude the amount of inhibitor needed for antibiotic sensitization. The selected antibiotic-EPI-PMBN combination caused a 10 million-fold reduction in the viability of biofilm forming cells. We proved that AMPs can synergize with EPIs and that this phenomenon can be exploited to sensitize bacteria to antibiotics.

Inhibition of Pseudomonas aeruginosa secreted virulence factors reduces lung inflammation in CF mice

Background: Cystic fibrosis (CF) lung infection is a complex condition where opportunistic pathogens and defective immune system cooperate in developing a constant cycle of infection and inflammation. The major pathogen, Pseudomonas aeruginosa, secretes a multitude of virulence factors involved in host immune response and lung tissue damage. In this study, we examined the possible anti-inflammatory effects of molecules inhibiting P. aeruginosa virulence factors.

Methods: Pyocyanin, pyoverdine and proteases were measured in bacterial culture supernatant from different P. aeruginosa strains. Inhibition of virulence factors by sub-inhibitory concentrations of clarithromycin and by protease inhibitors was evaluated. Lung inflammatory response was monitored by in vivo bioluminescence imaging in wild-type and CFTR-knockout mice expressing a luciferase gene under the control of a bovine IL-8 promoter.

Results: The amount of proteases, pyocyanin and pyoverdine secreted by P. aeruginosa strains was reduced after growth in the presence of a sub-inhibitory dose of clarithromycin. Intratracheal challenge with culture supernatant containing bacteria-released products induced a strong IL-8-mediated response in mouse lungs while lack of virulence factors corresponded to a reduction in bioluminescence emission. Particularly, sole inactivation of proteases by inhibitors Ilomastat and Marimastat also resulted in decreased lung inflammation.

Conclusions: Our data support the assumption that virulence factors are involved in P. aeruginosa pro-inflammatory action in CF lungs; particularly, proteases seem to play an important role. Inhibition of virulence factors production and activity resulted in decreased lung inflammation; thus, clarithromycin and protease inhibitors potentially represent additional therapeutic therapies for P. aeruginosa-infected patients.

Chronic Azithromycin Use in Cystic Fibrosis and Risk of Treatment-Emergent Respiratory Pathogens

RATIONALE

Azithromycin has been shown to improve lung function and reduce the number of pulmonary exacerbations in patients with cystic fibrosis. Concerns remain, however, regarding the potential emergence of treatment-related respiratory pathogens.

OBJECTIVES

To determine whether chronic azithromycin use (defined as three-times weekly administration) is associated with increased rates of detection of eight specific respiratory pathogens.

METHODS

We performed a new-user, propensity score-matched retrospective cohort study utilizing data from the Cystic Fibrosis Foundation Patient Registry. Incident azithromycin users were propensity score matched 1:1 with contemporaneous nonusers. Kaplan-Meier curves and Cox proportional hazards regression were used to evaluate the association between chronic azithromycin use and incident respiratory pathogen detection. Analyses were performed separately for each pathogen, limited to patients among whom that pathogen had not been isolated in the 2 years before cohort entry.

RESULTS

After propensity score matching, the mean age of the cohorts was approximately 12 years. Chronic azithromycin users had a significantly lower risk of detection of new methicillin-resistant Staphylococcus aureus, nontuberculous mycobacteria, and Burkholderia cepacia complex compared with nonusers. The risk of acquiring the remaining five pathogens was not significantly different between users and nonusers.

CONCLUSIONS

Using an innovative new-user, propensity score-matched study design to minimize indication and selection biases, we found in a predominantly pediatric cohort that chronic azithromycin users had a lower risk of acquiring several cystic fibrosis-related respiratory pathogens. These results may ease concerns that chronic azithromycin exposure increases the risk of acquiring new respiratory pathogens among pediatric patients with cystic fibrosis.

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.

Reemergence of Lower-Airway Microbiota in Lung Transplant Patients with Cystic Fibrosis

RATIONALE

Chronic lung infections are a hallmark of cystic fibrosis; they are responsible for progressive airway destruction and ultimately lead to respiratory death or the requirement for life-saving bilateral lung transplant. Furthermore, recurrent isolation of airway pathogens such as Pseudomonas aeruginosa in the allograft after transplant is associated with adverse outcomes, including bronchiolitis obliterans syndrome and acute infections. Little information exists on the impact of bilateral lung transplant on the lower-airway microbiota.

OBJECTIVES

To compare, at a microbiome and single-pathogen level (P. aeruginosa), the bacterial communities in pre- and post-transplant samples.

METHODS

We retrospectively accessed our biobank of sputum samples and sputum-derived bacterial pathogens for patients who had matched samples, including those who were clinically stable before transplant, those who had a pulmonary exacerbation before transplant, and those who had pulmonary exacerbation after transplant. We used 16S ribosomal RNA gene sequencing to characterize the lower-airway microbiome of 14 adult transplant patients with cystic fibrosis. Genotyping and phenotyping of P. aeruginosa isolates from 12 of these patients with matched isolates was performed.

MEASUREMENTS AND MAIN RESULTS

Although α-diversity (richness and evenness) of patient microbiomes was similar before and after transplant, β- diversity (core microbiome composition) measures stratified patients evenly into two groups with more similar and more dissimilar communities. P. aeruginosa strains isolated before transplant were found to reemerge in 11 of 12 patients; however, phenotypic variation was observed.

CONCLUSIONS

These findings indicate that recolonization by P. aeruginosa after transplant is almost always strain specific, suggesting a within-host source. The polymicrobial colonization of the airways after transplant does not always reflect the pretransplant sputum microbiota.

Physico-Chemical Properties, Aerosolization and Dissolution of Co-Spray Dried Azithromycin Particles with L-Leucine for Inhalation

PURPOSE

Inhalation therapy is popular to treat lower respiratory tract infections. Azithromycin is effective against some bacteria that cause respiratory tract infections; but it has poor water solubility that may limit its efficacy when administrated as inhalation therapy. In this study, dry powder inhaler formulations were developed by co-spray drying azithromycin with L-leucine with a purpose to improve dissolution.

METHODS

The produced powder formulations were characterized regarding particle size, morphology, surface composition and in-vitro aerosolization performance. Effects of L-leucine on the solubility and in-vitro dissolution of azithromycin were also evaluated.

RESULTS

The spray dried azithromycin alone formulation exhibited a satisfactory aerosol performance with a fine particle fraction (FPF) of 62.5 ± 4.1%. Addition of L-leucine in the formulation resulted in no significant change in particle morphology and FPF, which can be attributed to enrichment of azithromycin on the surfaces of composite particles. Importantly, compared with the spray-dried amorphous azithromycin alone powder, the co-spray dried powder formulations of azithromycin and L-leucine demonstrated a substantially enhanced in-vitro dissolution rate. Such enhanced dissolution of azithromycin could be attributed to the formation of composite system and the acidic microenvironment around azithromycin molecules created by the dissolution of acidic L-leucine in the co-spray dried powder. Fourier transform infrared spectroscopic data showed intermolecular interactions between azithromycin and L-leucine in the co-spray dried formulations.

CONCLUSIONS

We developed the dry powder formulations with satisfactory aerosol performance and enhanced dissolution for a poorly water soluble weak base, azithromycin, by co-spray drying with an amino acid, L-leucine.

Standard versus biofilm antimicrobial susceptibility testing to guide antibiotic therapy in cystic fibrosis

BACKGROUND

The antibiotics used to treat pulmonary infections in people with cystic fibrosis are typically chosen based on the results of antimicrobial susceptibility testing performed on bacteria traditionally grown in a planktonic mode (grown in a liquid). However, there is considerable evidence to suggest that Pseudomonas aeruginosa actually grows in a biofilm (or slime layer) in the airways of people with cystic fibrosis with chronic pulmonary infections. Therefore, choosing antibiotics based on biofilm rather than conventional antimicrobial susceptibility testing could potentially improve response to treatment of Pseudomonas aeruginosa in people with cystic fibrosis. This is an update of a previously published Cochrane Review.

OBJECTIVES

To compare biofilm antimicrobial susceptibility testing-driven therapy to conventional antimicrobial susceptibility testing-driven therapy in the treatment of Pseudomonas aeruginosa infection in people with cystic fibrosis.

SEARCH METHODS

We searched the Cochrane Cystic Fibrosis Trials Register, compiled from electronic database searches and handsearching of journals and conference abstract books. Most recent search: 19 June 2017.We also searched two ongoing trials registries and the reference lists of relevant articles and reviews. Most recent searches: 24 August 2017 and 05 September 2017.

SELECTION CRITERIA

Randomized controlled trials of antibiotic therapy based on biofilm antimicrobial susceptibility testing compared to antibiotic therapy based on conventional antimicrobial susceptibility testing in the treatment of Pseudomonas aeruginosa pulmonary infection in people with cystic fibrosis.

DATA COLLECTION AND ANALYSIS

Both authors independently selected trials, assessed their risk of bias and extracted data from eligible trials. Additionally, the review authors contacted the trial investigators to obtain further information. The quality of the evidence was assessed using the GRADE criteria.

MAIN RESULTS

The searches identified two multicentre, randomized, double-blind controlled clinical trials eligible for inclusion in the review with a total of 78 participants (adults and children); one trial was done in people who were clinically stable, the other in people experiencing pulmonary exacerbations. These trials prospectively assessed whether the use of biofilm antimicrobial susceptibility testing improved microbiological and clinical outcomes in participants with cystic fibrosis who were infected with Pseudomonas aeruginosa. The primary outcome was the change in sputum Pseudomonas aeruginosa density from the beginning to the end of antibiotic therapy.Although the intervention was shown to be safe, the data from these two trials did not provide evidence that biofilm susceptibility testing was superior to conventional susceptibility testing either in terms of microbiological or lung function outcomes. One of the trials also measured risk and time to subsequent exacerbation as well as quality of life measures and did not demonstrate any difference between groups in these outcomes. Both trials had an overall low risk of bias and the quality of the evidence using GRADE criteria was deemed to be moderate to high for the outcomes selected.

AUTHORS' CONCLUSIONS

The current evidence is insufficient to recommend choosing antibiotics based on biofilm antimicrobial susceptibility testing rather than conventional antimicrobial susceptibility testing in the treatment of Pseudomonas aeruginosa pulmonary infections in people with cystic fibrosis. Biofilm antimicrobial susceptibility testing may be more appropriate in the development of newer, more effective formulations of drugs which can then be tested in clinical trials.

Synthesis and Characterization of Nanocomposite Microparticles (nCmP) for the Treatment of Cystic Fibrosis-Related Infections

PURPOSE

Pulmonary antibiotic delivery is recommended as maintenance therapy for cystic fibrosis (CF) patients who experience chronic infections. However, abnormally thick and sticky mucus present in the respiratory tract of CF patients impairs mucus penetration and limits the efficacy of inhaled antibiotics. To overcome the obstacles of pulmonary antibiotic delivery, we have developed nanocomposite microparticles (nCmP) for the inhalation application of antibiotics in the form of dry powder aerosols.

METHODS

Azithromycin-loaded and rapamycin-loaded polymeric nanoparticles (NP) were prepared via nanoprecipitation and nCmP were prepared by spray drying and the physicochemical characteristics were evaluated.

RESULTS

The nanoparticles were 200 nm in diameter both before loading into and after redispersion from nCmP. The NP exhibited smooth, spherical morphology and the nCmP were corrugated spheres about 1 μm in diameter. Both drugs were successfully encapsulated into the NP and were released in a sustained manner. The NP were successfully loaded into nCmP with favorable encapsulation efficacy. All materials were stable at manufacturing and storage conditions and nCmP were in an amorphous state after spray drying. nCmP demonstrated desirable aerosol dispersion characteristics, allowing them to deposit into the deep lung regions for effective drug delivery.

CONCLUSIONS

The described nCmP have the potential to overcome mucus-limited pulmonary delivery of antibiotics.

Biofilm-related infections: bridging the gap between clinical management and fundamental aspects of recalcitrance toward antibiotics

Surface-associated microbial communities, called biofilms, are present in all environments. Although biofilms play an important positive role in a variety of ecosystems, they also have many negative effects, including biofilm-related infections in medical settings. The ability of pathogenic biofilms to survive in the presence of high concentrations of antibiotics is called "recalcitrance" and is a characteristic property of the biofilm lifestyle, leading to treatment failure and infection recurrence. This review presents our current understanding of the molecular mechanisms of biofilm recalcitrance toward antibiotics and describes how recent progress has improved our capacity to design original and efficient strategies to prevent or eradicate biofilm-related infections.

Standard versus biofilm antimicrobial susceptibility testing to guide antibiotic therapy in cystic fibrosis

BACKGROUND

The antibiotics used to treat pulmonary infections in people with cystic fibrosis are typically chosen based on the results of antimicrobial susceptibility testing performed on bacteria traditionally grown in a planktonic mode (grown in a liquid). However, there is considerable evidence to suggest that Pseudomonas aeruginosa actually grows in a biofilm (or slime layer) in the airways of people with cystic fibrosis with chronic pulmonary infections. Therefore, choosing antibiotics based on biofilm rather than conventional antimicrobial susceptibility testing could potentially improve response to treatment of Pseudomonas aeruginosa in people with cystic fibrosis. This is an update of a previously published Cochrane Review.

OBJECTIVES

To compare biofilm antimicrobial susceptibility testing-driven therapy to conventional antimicrobial susceptibility testing-driven therapy in the treatment of Pseudomonas aeruginosa infection in people with cystic fibrosis.

SEARCH METHODS

We searched the Cochrane Cystic Fibrosis Trials Register, compiled from electronic database searches and handsearching of journals and conference abstract books. We also searched a registry of ongoing trials and the reference lists of relevant articles and reviews.Most recent search: 19 November 2014.

SELECTION CRITERIA

Randomized controlled trials of antibiotic therapy based on biofilm antimicrobial susceptibility testing compared to antibiotic therapy based on conventional antimicrobial susceptibility testing in the treatment of Pseudomonas aeruginosa pulmonary infection in people with cystic fibrosis.

DATA COLLECTION AND ANALYSIS

Both authors independently selected trials, assessed their risk of bias and extracted data from eligible trials. Additionally, the review authors contacted the trial investigators to obtain further information.

MAIN RESULTS

The searches identified two multicentre, randomized, double-blind controlled clinical trials eligible for inclusion in the review with a total of 78 participants; one trial was done in people who were clinically stable, the other in people experiencing pulmonary exacerbations. These trials prospectively assessed whether the use of biofilm antimicrobial susceptibility testing improved microbiological and clinical outcomes in participants with cystic fibrosis who were infected with Pseudomonas aeruginosa. The primary outcome was the change in sputum Pseudomonas aeruginosa density from the beginning to the end of antibiotic therapy.Although the intervention was shown to be safe, the data from these two trials did not provide evidence that biofilm susceptibility testing was superior to conventional susceptibility testing either in terms of microbiological or lung function outcomes. One of the trials also measured risk and time to subsequent exacerbation as well as quality of life measures and did not demonstrate any difference between groups in these outcomes. Both trials had an overall low risk of bias.

AUTHORS' CONCLUSIONS

The current evidence is insufficient to recommend choosing antibiotics based on biofilm antimicrobial susceptibility testing rather than conventional antimicrobial susceptibility testing in the treatment of Pseudomonas aeruginosa pulmonary infections in people with cystic fibrosis. Biofilm antimicrobial susceptibility testing may be more appropriate in the development of newer, more effective formulations of drugs which can then be tested in clinical trials.

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.

Azithromycin and ciprofloxacin: a possible synergistic combination against Pseudomonas aeruginosa biofilm-associated urinary tract infections

Biofilm formation is becoming a predominant feature in nosocomial infections. Since biofilms are increasingly resistant to antibiotics, making monotherapy ineffective, combination therapy appears to be relevant for their eradication. This study assessed the potential of azithromycin (AZM) and ciprofloxacin (CIP) alone and in combination in vitro and in a mouse model of urinary tract infection (UTI) induced with biofilm cells of Pseudomonas aeruginosa. In vitro antibacterial and antibiofilm activities of antibiotics alone and in combination were assessed using the fractional inhibitory concentration index (FICI), time-kill analysis and confocal laser scanning microscopy (CLSM). In vivo efficacy was evaluated in a UTI model by quantitation of bacterial burden in kidney and bladder tissue, renal histopathology, pathology index factors (MDA and NO), and pro-inflammatory (MIP-2 and IL-6) and anti-inflammatory (IL-10) cytokines. MICs of AZM and CIP for strain PAO1 were 256 and 0.5 μg/mL, respectively; MBECs were 4096 and 1024 μg/mL. Synergistic interaction was observed between AZM and CIP both against planktonic and biofilm bacteria (FICI<0.5). The combination was also able to inhibit biofilm formation (at MIC levels) as observed with CLSM. Oral therapy with AZM (500 mg/kg) and CIP (30 mg/kg) combination in mice for 4 days showed accelerated clearance of bacteria from kidney and bladder tissue, improved renal histopathology, decreased levels of MDA and NO, significant decline in MIP-2 and IL-6, and increased IL-10 in the kidney (P<0.0001). We conclude that AZM+CIP therapy holds promise against biofilm-associated UTIs as it confers antibacterial, immunomodulatory and anti-inflammatory effects.

Azithromycin analogue CSY0073 attenuates lung inflammation induced by LPS challenge

BACKGROUND AND PURPOSE

Azithromycin is a macrolide antibiotic with anti-inflammatory and immunomodulating effects. Long-term azithromycin therapy in patients with chronic lung diseases such as cystic fibrosis has been associated with increased antimicrobial resistance, emergence of hypermutable strains, ototoxicity and cardiac toxicity. The aim of this study was to assess the anti-inflammatory effects of the non-antibiotic azithromycin derivative CSY0073.

EXPERIMENTAL APPROACH

We compared the effects of CSY0073 with those of azithromycin in experiments on bacterial cultures, Pseudomonas aeruginosa biofilm, lung cells and mice challenged intranasally with P. aeruginosa LPS.

KEY RESULTS

In contrast to azithromycin, CSY0073 did not inhibit the growth of P. aeruginosa, Staphylococcus aureus or Haemophilus influenzae and had no effect on an established P. aeruginosa biofilm. Bronchoalveolar lavage (BAL) fluids and lung homogenates collected after the LPS challenge in mice showed that CSY0073 and azithromycin (200 mg·kg(-1), i.p.) decreased neutrophil counts at 24 h and TNF-α, CXCL1 and CXCL2 levels in the BAL fluid after 3 h and IL-6, CXCL2 and IL-1β levels in the lung after 3 h compared with the vehicle. However, only azithromycin reduced IL-1β levels in the lung 24 h post LPS challenge. CSY0073 and azithromycin similarly diminished the production of pro-inflammatory cytokines by macrophages, but not lung epithelial cells, exposed to P. aeruginosa LPS.

CONCLUSIONS AND IMPLICATIONS

Unlike azithromycin, CSY0073 had no antibacterial effects but it did have a similar anti-inflammatory profile to that of azithromycin. Hence, CSY0073 may have potential as a long-term treatment for patients with chronic lung diseases.

Increased IL-8 production in human bronchial epithelial cells after exposure to azithromycin-pretreated Pseudomonas aeruginosa in vitro

Although Pseudomonas aeruginosa is not typically susceptible to azithromycin (AZM) in in vitro tests, AZM improves the clinical outcome in patients with chronic respiratory infections, in which both the modulation of the host immune system and of bacterial virulence by AZM are thought to play an important role. However, there is currently little direct evidence showing the impact of bacteria pretreated with AZM on epithelial cells, which represents the first barrier to infecting P. aeruginosa. In this study, we pretreated P. aeruginosa with AZM and subsequently infected human bronchial epithelial cells (HBEs) in the absence of AZM. The results showed that AZM-pretreated P. aeruginosa (PAO1 and six different clinical isolates) significantly stimulated HBE cells to release IL-8, a crucial pro-inflammatory cytokine. This effect was not observed in a P. aeruginosa PAO1 mutant strain unable to produce the type III secretion system effector gene pcrV (strain PW4017). Our results suggest that AZM-pretreated P. aeruginosa could indirectly exacerbate pro-inflammation by inducing IL-8 production in HBEs.

The PhtL protein of Pseudomonas syringae pv. phaseolicola NPS3121 affects the expression of both phaseolotoxin cluster (Pht) and Non-Pht encoded genes

Pseudomonas syringae pv. phaseolicola, the causal agent of halo blight disease in bean, produces a toxin known as phaseolotoxin, whose synthesis involves the products of some of the genes found within the Pht region. This region, considered a pathogenicity island, comprises 23 genes arranged in five transcriptional units: two single-gene units (argK, phtL) and three arranged as operons (phtA, phtD, phtM), most with unknown function. In P. syringae pv. phaseolicola, maximal expression of most of the genes encoded in the Pht region and the synthesis of phaseolotoxin require the product of the phtL gene, of unknown function but that has been proposed to have a regulatory role. In order to evaluate the role of phtL gene in P. syringae pv. phaseolicola, we performed a comparative transcriptional analysis with the wild type and a phtL(-) mutant strains using microarrays. The microarray data analysis showed that PhtL regulates the expression not only of genes within the Pht region, but also alters the expression of genomic genes outside it, indicating that this gene has been integrated into the regulatory machinery of the bacterium. The expression changes of many of those genes were confirmed by RT-PCR. This study also demonstrated the importance of the PhtL protein in the process of iron response, and suggests that the effect of PhtL on the expression of pathogenicity related, respiration and oxidative stress genes, observed in this study, appears to be indirect through its influence on the Fur protein expression.

Interference of bacterial cell-to-cell communication: a new concept of antimicrobial chemotherapy breaks antibiotic resistance

Bacteria use a cell-to-cell communication activity termed "quorum sensing" to coordinate group behaviors in a cell density dependent manner. Quorum sensing influences the expression profile of diverse genes, including antibiotic tolerance and virulence determinants, via specific chemical compounds called "autoinducers". During quorum sensing, Gram-negative bacteria typically use an acylated homoserine lactone (AHL) called autoinducer 1. Since the first discovery of quorum sensing in a marine bacterium, it has been recognized that more than 100 species possess this mechanism of cell-to-cell communication. In addition to being of interest from a biological standpoint, quorum sensing is a potential target for antimicrobial chemotherapy. This unique concept of antimicrobial control relies on reducing the burden of virulence rather than killing the bacteria. It is believed that this approach will not only suppress the development of antibiotic resistance, but will also improve the treatment of refractory infections triggered by multi-drug resistant pathogens. In this paper, we review and track recent progress in studies on AHL inhibitors/modulators from a biological standpoint. It has been discovered that both natural and synthetic compounds can disrupt quorum sensing by a variety of means, such as jamming signal transduction, inhibition of signal production and break-down and trapping of signal compounds. We also focus on the regulatory elements that attenuate quorum sensing activities and discuss their unique properties. Understanding the biological roles of regulatory elements might be useful in developing inhibitor applications and understanding how quorum sensing is controlled.

Phenotypic heterogeneity of Pseudomonas aeruginosa populations in a cystic fibrosis patient

The opportunistic pathogen Pseudomonas aeruginosa chronically infects the lower airways of patients with cystic fibrosis. Throughout the course of infection this organism undergoes adaptations that contribute to its long-term persistence in the airways. While P. aeruginosa diversity has been documented, it is less clear to what extent within-patient diversity contributes to the overall population structure as most studies have been limited to the analysis of only a few isolates per patient per time point. To examine P. aeruginosa population structure in more detail we collected multiple isolates from individual sputum samples of a patient chronically colonized with P. aeruginosa. This strain collection, comprised of 169 clonal isolates and representing three pulmonary exacerbations as well as clinically stable periods, was assayed for a wide selection of phenotypes. These phenotypes included colony morphology, motility, quorum sensing, protease activity, auxotrophy, siderophore levels, antibiotic resistance, and growth profiles. Each phenotype displayed significant variation even within isolates of the same colony morphotype from the same sample. Isolates demonstrated a large degree of individuality across phenotypes, despite being part of a single clonal lineage, suggesting that the P. aeruginosa population in the cystic fibrosis airways is being significantly under-sampled.

Effects of azithromycin in Pseudomonas aeruginosa burn wound infection

BACKGROUND

Cutaneous thermal injuries (i.e., burns) remain a common form of debilitating trauma, and outcomes are often worsened by wound infection with environmental bacteria, chiefly Pseudomonas aeruginosa.

MATERIALS AND METHODS

We tested the effects of early administration of a single dose of azithromycin, with or without subsequent antipseudomonal antibiotics, in a mouse model of standardized thermal injury infected with P aeruginosa via both wound site and systemic infection. We also tested the antimicrobial effects of these antibiotics alone or combined in comparative biofilm and planktonic cultures in vitro.

RESULTS

In our model, early azithromycin administration significantly reduced wound and systemic infection without altering wound site or circulating neutrophil activity. The antimicrobial effect of azithromycin was additive with ciprofloxacin but significantly reduced the antimicrobial effect of tobramycin. This pattern was reproduced in biofilm cultures and not observed in planktonic cultures of P aeruginosa.

CONCLUSION

These data suggest that early administration of azithromycin following burn-related trauma and infection may reduce P aeruginosa infection and potential interactions with other antibiotics should be considered when designing future studies.

Standard versus biofilm antimicrobial susceptibility testing to guide antibiotic therapy in cystic fibrosis

BACKGROUND

The antibiotics used to treat pulmonary infections in people with cystic fibrosis are typically chosen based on the results of antimicrobial susceptibility testing performed on bacteria traditionally grown in a planktonic mode (grown in a liquid). However, there is considerable evidence to suggest that Pseudomonas aeruginosa actually grows in a biofilm (or slime layer) in the airways of cystic fibrosis patients with chronic pulmonary infections. Therefore, choosing antibiotics based on biofilm rather than conventional antimicrobial susceptibility testing could potentially improve response to treatment of Pseudomonas aeruginosa in people with cystic fibrosis.

OBJECTIVES

To compare biofilm antimicrobial susceptibility testing-driven therapy to conventional antimicrobial susceptibility testing-driven therapy in the treatment of Pseudomonas aeruginosa infection in people with cystic fibrosis.

SEARCH METHODS

We searched the Cochrane Cystic Fibrosis Trials Register, compiled from electronic database searches and handsearching of journals and conference abstract books. We also searched a registry of ongoing trials and the reference lists of relevant articles and reviews.Most recent search: 02 August 2012.

SELECTION CRITERIA

Randomized controlled trials of antibiotic therapy based on biofilm antimicrobial susceptibility testing compared to antibiotic therapy based on conventional antimicrobial susceptibility testing in the treatment of Pseudomonas aeruginosa pulmonary infection in individuals with cystic fibrosis.

DATA COLLECTION AND ANALYSIS

Both authors independently selected trials, assessed their risk of bias and extracted data from eligible trials. Additionally, the authors contacted the trial investigators to obtain further information.

MAIN RESULTS

The search identified one multicentre, randomized, double-blind controlled clinical trial eligible for inclusion in the review (39 participants). This trial prospectively assessed whether the use of biofilm antimicrobial susceptibility testing improved microbiological and clinical outcomes in participants with cystic fibrosis who were infected with Pseudomonas aeruginosa. The primary outcome was the change in sputum Pseudomonas aeruginosa density from the beginning to the end of antibiotic therapy. The mean (standard deviation) change in density in log(10) colony forming units per gram was -2.94 (2.83) in the biofilm group and -3.27 (3.09) in the control group, for a mean difference of 0.28 (95% confidence interval -1.98 to 2.54) (P = 0.8). The data did not provide evidence that biofilm susceptibility testing was superior to conventional susceptibility testing.

AUTHORS' CONCLUSIONS

The current evidence is insufficient to recommend choosing antibiotics based on biofilm antimicrobial susceptibility testing rather than conventional antimicrobial susceptibility testing in the treatment of Pseudomonas aeruginosa pulmonary infections in people with cystic fibrosis. Future randomized clinical trials on this topic may shed further light on this question.

Azithromycin maintenance therapy in patients with cystic fibrosis: a dose advice based on a review of pharmacokinetics, efficacy, and side effects

Azithromycin maintenance therapy results in improvement of respiratory function in patients with cystic fibrosis (CF). In azithromycin maintenance therapy, several dosing schemes are applied. In this review, we combine current knowledge about azithromycin pharmacokinetics with the dosing schedules used in clinical trials in order to come to a dosing advise which could be generally applicable. We used data from a recently updated Cochrane meta analysis (2011), the reports of clinical trials and pharmacokinetic studies. Based on these data, it was concluded that a dose level of 22-30 mg/kg/week is the lowest dose level with proven efficacy. Due to the extended half-life in patients with CF, the weekly dose of azithromycin can be divided in one to seven dosing moments, depending on patient preference and gastro-intestinal tolerance. No important side effects or interactions with other CF-related drugs have been documented so far.

Macrolides: from in vitro anti-inflammatory and immunomodulatory properties to clinical practice in respiratory diseases

BACKGROUND

Macrolides have long been recognised to exert immunomodulary and anti-inflammatory actions. They are able to suppress the "cytokine storm" of inflammation and to confer an additional clinical benefit through their immunomodulatory properties.

METHODS

A search of electronic journal articles was performed using combinations of the following keywords: macrolides, COPD, asthma, bronchitis, bronchiolitis obliterans, cystic fibrosis, immunomodulation, anti-inflammatory effect, diabetes, side effects and systemic diseases.

RESULTS

Macrolide effects are time- and dose-dependent, and the mechanisms underlying these effects remain incompletely understood. Both in vitro and in vivo studies have provided ample evidence of their immunomodulary and anti-inflammatory actions. Importantly, this class of antibiotics is efficacious with respect to controlling exacerbations of underlying respiratory problems, such as cystic fibrosis, asthma, bronchiectasis, panbrochiolitis and cryptogenic organising pneumonia. Macrolides have also been reported to reduce airway hyper-responsiveness and improve pulmonary function.

CONCLUSION

This review provides an overview on the properties of macrolides (erythromycin, clarithromycin, roxithromycin, azithromycin), their efficacy in various respiratory diseases and their adverse effects.

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.

Prevention of siderophore- mediated gut-derived sepsis due to P. aeruginosa can be achieved without iron provision by maintaining local phosphate abundance: role of pH

Background

During extreme physiological stress, the intestinal tract can be transformed into a harsh environment characterized by regio- spatial alterations in oxygen, pH, and phosphate concentration. When the human intestine is exposed to extreme medical interventions, the normal flora becomes replaced by pathogenic species whose virulence can be triggered by various physico-chemical cues leading to lethal sepsis. We previously demonstrated that phosphate depletion develops in the mouse intestine following surgical injury and triggers intestinal P. aeruginosa to express a lethal phenotype that can be prevented by oral phosphate ([Pi]) supplementation.

Results

In this study we examined the role of pH in the protective effect of [Pi] supplementation as it has been shown to be increased in the distal gut following surgical injury. Surgically injured mice drinking 25 mM [Pi] at pH 7.5 and intestinally inoculated with P. aeruginosa had increased mortality compared to mice drinking 25 mM [Pi] at pH 6.0 (p < 0.05). This finding was confirmed in C. elegans. Transcriptional analysis of P. aeruginosa demonstrated enhanced expression of various genes involved in media alkalization at pH 6.0 and a global increase in the expression of all iron-related genes at pH 7.5. Maintaining the pH at 6.0 via phosphate supplementation led to significant attenuation of iron-related genes as demonstrated by microarray and confirmed by QRT-PCR analyses.

Conclusion

Taken together, these data demonstrate that increase in pH in distal intestine of physiologically stressed host colonized by P. aeruginosa can lead to the expression of siderophore-related virulence in bacteria that can be prevented without providing iron by maintaining local phosphate abundance at pH 6.0. This finding is particularly important as provision of exogenous iron has been shown to have untoward effects when administered to critically ill and septic patients. Given that phosphate, pH, and iron are near universal cues that dictate the virulence status of a broad range of microorganisms relevant to serious gut origin infection and sepsis in critically ill patients, the maintenance of phosphate and pH at appropriate physiologic levels to prevent virulence activation in a site specific manner can be considered as a novel anti-infective therapy in at risk patients.

Pseudomonas aeruginosa in cystic fibrosis: pyocyanin negative strains are associated with BPI-ANCA and progressive lung disease

The clinical consequence of chronic Pseudomonas aeruginosa colonization in cystic fibrosis (CF) varies between individuals for unknown reasons. Auto-antibodies against bactericidal/permeability increasing protein (BPI-ANCA) are associated with poor prognosis in CF. We hypothesize that there is a correlation between the presence of BPI-ANCA, the properties of the colonizing bacteria and the clinical conditions of the host. We compared isolates of P. aeruginosa from BPI-ANCA positive CF patients who have deteriorating lung disease with BPI-ANCA negative CF patients who are in stable clinical conditions. Epithelial cells (A549) and isolated polymorphonuclear granulocytes (PMNs) were stimulated with the isolates and cell death was analyzed with flow cytometry. We found that the ANCA associated strains in most cases showed pyocyanin negative phenotypes. These strains also induced less inflammatory response than the non-ANCA associated strains as shown by apoptosis and necrosis of epithelial cells and neutrophils. Our results suggest that colonization with strains of P. aeruginosa that induce a weak inflammatory response is associated with unfavorable outcome in CF. We speculate that inadequate control of pathogen proliferation through an insufficient inflammatory response results in a slowly increasing number of bacteria and accumulation of dying PMNs in the airways, contributing to progression in CF lung disease.

Azithromycin may inhibit interleukin-8 through suppression of Rac1 and a nuclear factor-kappa B pathway in KB cells stimulated with lipopolysaccharide

BACKGROUND

Recent studies have shown that the 15-member macrolide antibiotic azithromycin (AZM) not only has antibacterial activity, but also results in the role of immunomodulator. Interleukin (IL)-8 is an important inflammatory mediator in periodontal disease. However, there have been no reports on the effects of AZM on IL-8 production from human oral epithelium. Therefore, we investigated the effects of AZM on IL-8 production in an oral epithelial cell line.

METHODS

KB cells were stimulated by Escherichia coli or Aggregatibacter actinomycetemcomitans (previously Actinobacillus actinomycetemcomitans) lipopolysaccharide (LPS) with or without AZM. IL-8 mRNA and protein expression and production in response to LPS were analyzed by quantitative polymerase chain reaction, flow cytometry, and enzyme-linked immunosorbent assay. The activation of nuclear factor-kappa B (NF-κB) and Rac1, which is important for IL-8 expression, was analyzed by enzyme-linked immunosorbent assay and Western blotting, respectively.

RESULTS

IL-8 mRNA expression, IL-8 production, and NF-κB activation in LPS-stimulated KB cells were inhibited by the addition of AZM. LPS-induced Rac1 activation was also suppressed by AZM.

CONCLUSIONS

This study suggests that AZM inhibits LPS-induced IL-8 production in an oral epithelial cell line, in part caused by the suppression of Rac1 and NF-κB activation. The use of AZM might provide possible benefits in periodontal therapy, with respect to both its antibacterial action and apparent anti-inflammatory effect.

Chronic macrolide therapy in inflammatory airways diseases

Long-term therapy with the macrolide antibiotic erythromycin was shown to alter the clinical course of diffuse panbronchiolitis in the late 1980s. Since that time, macrolides have been found to have a large number of antiinflammatory properties in addition to being antimicrobials. These observations provided the rationale for many studies performed over the last decade to assess the usefulness of macrolides in other inflammatory airways diseases, such as cystic fibrosis, asthma, COPD, and bronchiolitis obliterans syndrome. This review summarizes the immunomodulatory properties of macrolides and the results of these recent studies demonstrating their potential for being disease-modifying agents.

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.

YfiBNR mediates cyclic di-GMP dependent small colony variant formation and persistence in Pseudomonas aeruginosa

During long-term cystic fibrosis lung infections, Pseudomonas aeruginosa undergoes genetic adaptation resulting in progressively increased persistence and the generation of adaptive colony morphotypes. This includes small colony variants (SCVs), auto-aggregative, hyper-adherent cells whose appearance correlates with poor lung function and persistence of infection. The SCV morphotype is strongly linked to elevated levels of cyclic-di-GMP, a ubiquitous bacterial second messenger that regulates the transition between motile and sessile, cooperative lifestyles. A genetic screen in PA01 for SCV-related loci identified the yfiBNR operon, encoding a tripartite signaling module that regulates c-di-GMP levels in P. aeruginosa. Subsequent analysis determined that YfiN is a membrane-integral diguanylate cyclase whose activity is tightly controlled by YfiR, a small periplasmic protein, and the OmpA/Pal-like outer-membrane lipoprotein YfiB. Exopolysaccharide synthesis was identified as the principal downstream target for YfiBNR, with increased production of Pel and Psl exopolysaccharides responsible for many characteristic SCV behaviors. An yfi-dependent SCV was isolated from the sputum of a CF patient. Consequently, the effect of the SCV morphology on persistence of infection was analyzed in vitro and in vivo using the YfiN-mediated SCV as a representative strain. The SCV strain exhibited strong, exopolysaccharide-dependent resistance to nematode scavenging and macrophage phagocytosis. Furthermore, the SCV strain effectively persisted over many weeks in mouse infection models, despite exhibiting a marked fitness disadvantage in vitro. Exposure to sub-inhibitory concentrations of antibiotics significantly decreased both the number of suppressors arising, and the relative fitness disadvantage of the SCV mutant in vitro, suggesting that the SCV persistence phenotype may play a more important role during antimicrobial chemotherapy. This study establishes YfiBNR as an important player in P. aeruginosa persistence, and implicates a central role for c-di-GMP, and by extension the SCV phenotype in chronic infections.

During long-term chronic infections of cystic fibrosis patients, Pseudomonas aeruginosa adapts to the lung environment, generating various different morphotypes including small colony variants (SCVs), small, strongly adherent colonies whose appearance correlates with persistence of infection. The SCV morphology is strongly associated with increased levels of the signaling molecule cyclic di-GMP. In this study we investigated the connection between cyclic di-GMP, SCV and persistence of infection. Following a genetic screen for mutants that displayed SCV morphologies, we identified and characterized the YfiBNR system. YfiN is a membrane-bound cyclic di-GMP producing enzyme, whose activity is tightly controlled by YfiR and YfiB. Cyclic di-GMP produced by YfiN boosts exopolysaccharide synthesis, generating an SCV morphotype upon YfiR-mediated release of YfiN repression. The resulting YfiN-mediated SCV morphotype is highly resistant to macrophage phagocytosis in vitro, suggesting a role for the SCV phenotype in immune system evasion. Consistent with this, YfiN de-repression increased the persistence of P. aeruginosa in long-term infections in a mouse model. The observation that the addition of antibiotics decreased the number of suppressors, and the relative fitness disadvantage of the YfiN-mediated SCV morphotype in liquid culture, suggested that SCV-mediated persistence might be favored during antimicrobial chemotherapy.

Attenuation of Pseudomonas aeruginosa virulence factors and biofilms by co-encapsulation of bismuth-ethanedithiol with tobramycin in liposomes

OBJECTIVES

This study examined the activities of tobramycin and bismuth against quorum sensing, virulence factors and biofilms of Pseudomonas aeruginosa by co-encapsulating the agents in liposomes in order to achieve greater delivery of the agents.

METHODS

The inhibitory effects of the agents, in either their conventional (free) or vesicle-entrapped (liposomal) formulations, were assessed by measuring the changes in the quorum-sensing signal molecule N-acyl homoserine lactone, pyoverdine, pyocyanin, elastase, protease, chitinase, bacterial attachment and biofilms in vitro.

RESULTS

The effectiveness of tobramycin and bismuth was superior when they were co-administered as a liposomal formulation as measured by their ability to attenuate the production of N-acyl homoserine lactone, elastase (P < 0.01), protease (P < 0.05) and chitinase (P < 0.01). In the presence of non-lethal concentrations of free and liposomal tobramycin and bismuth, bacterial attachment was attenuated. Biofilm formation was also attenuated with free tobramycin and bismuth, yet, in the presence of liposomal tobramycin and bismuth, biofilm complexes could form but contained mostly dead bacteria. When established biofilms were treated with higher concentrations, free tobramycin and bismuth killed and detached bacteria, while the liposomal tobramycin and bismuth penetrated and killed bacteria in the cores of the biofilms.

CONCLUSIONS

These data suggest that treatment of P. aeruginosa with tobramycin and bismuth, as measured by the changes in quorum sensing, virulence factors and biofilms, is most effective when delivered as a liposomal formulation at a lower concentration compared with the free formulation.

Azithromycin treatment alters gene expression in inflammatory, lipid metabolism, and cell cycle pathways in well-differentiated human airway epithelia

Prolonged macrolide antibiotic therapy at low doses improves clinical outcome in patients affected with diffuse panbronchiolitis and cystic fibrosis. Consensus is building that the therapeutic effects are due to anti-inflammatory, rather than anti-microbial activities, but the mode of action is likely complex. To gain insights into how the macrolide azithromycin (AZT) modulates inflammatory responses in airways, well-differentiated primary cultures of human airway epithelia were exposed to AZT alone, an inflammatory stimulus consisting of soluble factors from cystic fibrosis airways, or AZT followed by the inflammatory stimulus. RNA microarrays were conducted to identify global and specific gene expression changes. Analysis of gene expression changes revealed that the AZT treatment alone altered the gene profile of the cells, primarily by significantly increasing the expression of lipid/cholesterol genes and decreasing the expression of cell cycle/mitosis genes. The increase in cholesterol biosynthetic genes was confirmed by increased filipin staining, an index of free cholesterol, after AZT treatment. AZT also affected genes with inflammatory annotations, but the effect was variable (both up- and down-regulation) and gene specific. AZT pretreatment prevented the up-regulation of some genes, such as MUC5AC and MMP9, triggered by the inflammatory stimulus, but the up-regulation of other inflammatory genes, e.g., cytokines and chemokines, such as interleukin-8, was not affected. On the other hand, HLA genes were increased by AZT. Notably, secreted IL-8 protein levels did not reflect mRNA levels, and were, in fact, higher after AZT pretreatment in cultures exposed to the inflammatory stimulus, suggesting that AZT can affect inflammatory pathways other than by altering gene expression. These findings suggest that the specific effects of AZT on inflamed and non-inflamed airway epithelia are likely relevant to its clinical activity, and their apparent complexity may help explain the diverse immunomodulatory roles of macrolides.

Human neutrophil peptides and phagocytic deficiency in bronchiectatic lungs

RATIONALE

A well-known clinical paradox is that severe bacterial infections persist in the lungs of patients with cystic fibrosis (CF) despite the abundance of polymorphonuclear neutrophils (PMN) and the presence of a high concentration of human neutrophil peptides (HNP), both of which are expected to kill the bacteria but fail to do so. The mechanisms remain unknown.

OBJECTIVES

This study examined several possible mechanisms to understand this paradox.

METHODS

PMN were isolated from sputum and blood of subjects with and without CF or non-CF bronchiectasis for phagocytic assays. HNP isolated from patients with CF were used to stimulate healthy PMN followed by phagocytic tests.

MEASUREMENTS AND MAIN RESULTS

PMN isolated from the sputum of the bronchiectatic patients display defective phagocytosis that correlated with high concentrations of HNP in the lung. When healthy PMN were incubated with HNP, decreased phagocytic capacity was observed in association with depressed surface Fc gamma RIII, actin-filament remodeling, enhanced intracellular Ca(2+), and degranulation. Treatment of PMN with an intracellular Ca(2+) blocker or alpha1-proteinase inhibitor to attenuate the activity of HNP largely prevented the HNP-induced phagocytic deficiency. Intratracheal instillation of HNP in Pallid mice (genetically deficient in alpha1-proteinase inhibitor) resulted in a greater PMN lung infiltration and phagocytic deficiency compared with wild-type mice.

CONCLUSIONS

HNP or PMN alone exert antimicrobial ability, which was lost as a result of their interaction. These effects of HNP may help explain the clinical paradox seen in patients with inflammatory lung diseases, suggesting HNP as a novel target for clinical therapy.

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.