Effects of azithromycin in Pseudomonas aeruginosa burn wound infection

Anti-Biofilm Enzymes-Assisted Antibiotic Therapy against Burn Wound Infection by Pseudomonas aeruginosa

Pseudomonas aeruginosa can form biofilms at the site of burn wound, leading to infection and the failure of treatment regimens. The previous in vitro study demonstrated that a combination of the quorum-quenching enzyme AidHA147G and the extracellular matrix hydrolase PslG was effective in inhibiting biofilm and promoting antibiotic synergy. The aim of the present study was to evaluate the efficacy of this combination of enzymes in conjunction with tobramycin in treating burn wound infected with P. aeruginosa. The results showed that this treatment was effective in quorum-quenching and biofilm inhibition on infected wounds. Compared with the tobramycin treatment only, simultaneous treatment with the enzymes and antibiotics significantly reduced the severity of tissue damage, decreased the bacterial load, and reduced the expression of the inflammatory indicators myeloperoxidase (MPO) and malondialdehyde (MDA). Topical application of the enzymes also reduced the bacterial load and inflammation to some extent. These results indicate that the combined-enzyme approach is a potentially effective treatment for P. aeruginosa biofilm infections of burn wounds.

Anti-inflammatory and antibacterial potential of Ajwa date (Phoenix dactylifera L.) extract in burn infection

Thermal burns produce tissue damage, which eliminates the protective role of tissue. Due to the extensive tissue damage from severe burns, an overactive immune response occurs. Furthermore, this raises the possibility of getting sepsis, a condition in which a bacterial infection spreads throughout the body rather than only in the area of the injury or localized infection. To determine the compounds of Ajwa dates have the potential as an anti-inflammatory and antibacterial agent in infectious thermal burns. The research method used the Preferred Reporting Items for Systematic Review and Meta-Analyses guideline. Various references were collected from the online database Google Scholar and PubMed including reports, journals, and all references mostly published no more than the past 10 years. This systematic review revealed 16 research articles that were pertinent. Polyphenolic substances such as flavonoids, glycosides, and phenolic acids were found in ajwa dates. Specified polyphenol chemicals have the ability to interact with one or more immune cell receptors, moving intracellular messages and influencing the host's immunological response. Ajwa dates' polyphenol acts as an anti-inflammatory agent in severe burns by inhibiting the expression of pathogen-associated molecular pattern receptors, controlling transcription factors, and changing the phenotype of macrophage cells, among other ways. The bacterial activity and immune response regulation of Ajwa dates, on the other hand, also serve as an antibacterial agent directly. The polyphenol compounds in Ajwa dates have the potential to operate as an anti-inflammatory and antibacterial agent in infected thermal burns.

Testing the effects of combining azithromycin with inhaled tobramycin for P. aeruginosa in cystic fibrosis: a randomised, controlled clinical trial

RATIONALE

Inhaled tobramycin and oral azithromycin are common chronic therapies in people with cystic fibrosis and Pseudomonas aeruginosa airway infection. Some studies have shown that azithromycin can reduce the ability of tobramycin to kill P. aeruginosa. This trial was done to test the effects of combining azithromycin with inhaled tobramycin on clinical and microbiological outcomes in people already using inhaled tobramycin. We theorised that those randomised to placebo (no azithromycin) would have greater improvement in forced expiratory volume in one second (FEV1) and greater reduction in P. aeruginosa sputum in response to tobramycin.

METHODS

A 6-week prospective, randomised, placebo-controlled, double-blind trial testing oral azithromycin versus placebo combined with clinically prescribed inhaled tobramycin in individuals with cystic fibrosis and P. aeruginosa airway infection.

RESULTS

Over a 6-week period, including 4 weeks of inhaled tobramycin, the relative change in FEV1 did not statistically significantly differ between groups (azithromycin (n=56) minus placebo (n=52) difference: 3.44%; 95% CI: -0.48 to 7.35; p=0.085). Differences in secondary clinical outcomes, including patient-reported symptom scores, weight and need for additional antibiotics, did not significantly differ. Among the 29 azithromycin and 35 placebo participants providing paired sputum samples, the 6-week change in P. aeruginosa density differed in favour of the placebo group (difference: 0.75 log10 CFU/mL; 95% CI: 0.03 to 1.47; p=0.043).

CONCLUSIONS

Despite having greater reduction in P. aeruginosa density in participants able to provide sputum samples, participants randomised to placebo with inhaled tobramycin did not experience significantly greater improvements in lung function or other clinical outcomes compared with those randomised to azithromycin with tobramycin.

Long-term, low-dose macrolide antibiotic treatment in pediatric chronic airway diseases

Macrolide antibiotics are one of the most commonly used broad-spectrum antibiotics. They have an inhibitory effect on a variety of respiratory pathogens; besides, they have non-anti-infective effects, including anti-inflammatory, regulating airway secretion, immune regulation, and other effects. A growing number of studies have shown that the non-anti-infective effects of macrolides have important and potential value in the treatment of pediatric chronic airway diseases; the therapy was described as "long-term, low-dose usage"; unfortunately, there is no guideline or consensus that applies to children. To better carry out the mechanism and clinical research of non-anti-infective effect and promote its rational use in children, the authors summarize the evidence of the usage of long-term, low-dose macrolide antibiotic therapy (LLMAT) in the treatment of chronic airway diseases in children and the progress in recent years. IMPACT: This review summarizes the evidence (mostly in recent 5 years) of the usage of long-term, low-dose macrolide antibiotic therapy in the treatment of chronic airway diseases. The recent studies and guidelines support and enrich the point that long-term, low-dose macrolide antibiotic therapy has potential benefit for children with severe asthma, CF, non-CF bronchiectasis, and BO, which provides clinical references and is of clinical interest. Long-term, low-dose macrolide antibiotic therapy has good safety, and no serious events have been reported; however, potential cardiac side effects and macrolide resistance should be clinically noted.

NLRP3 knockout enhances immune infiltration and inflammatory responses and improves survival in a burn sepsis model

Although sepsis in burn patients is a major contributor to mortality, treatments are not always effective and underlying mechanisms have yet to be completely elucidated. NLRP3 inflammasome orchestrates burn-induced, inflammatory-driven pathophysiologic processes. Here, we determined the mechanism of NLRP3 inflammasome activation on bacterial clearance and mortality in burn sepsis. We obtained tissue and blood from 30 wild-type and 30 Nlrp3^-/- mice. Mice were subjected to a two-hit model of 25-30% TBSA scald burn followed by Pseudomonas aeruginosa wound infection 72 hours after injury. We also obtained tissue from 34 adult burn patients (≥18 years of age) with early (0-11 days post-burn) and later (≥12 days post-burn) surgical time-points and ten healthy controls. Murine studies indicated that Nlrp3^-/- had 30% improved survival and bacterial clearance at the site of injury and is systemically relative to burn sepsis wild type. Greater macrophage and neutrophil infiltration occurred acutely after infection (12 hours) to the site of injury and adipose tissue. This was followed by increased macrophage and neutrophil infiltration to lymphoid organs and liver beyond the acute phase (24 and 72 hours). Interestingly, Nlrp3 ablation increased acute systemic inflammation (IL-6, TNF-α, IL-1β). Septic burn patients had persistently increased adipose NLRP3 by-product expression beyond the acute phase that was more pronounced in late-onset sepsis. Our findings suggest that Nlrp3 genetic ablation enhanced acute tissue-specific inflammatory responsiveness. Likely, this occurs by paradoxically increasing acute immune infiltration and inflammation with a non-persistent response. Clinically, persistent NLRP3-mediated inflammation occurs in septic versus normal burn patients and potentially detrimentally impacts patient outcomes.

Effect of Concomitant Azithromycin and Tobramycin Use on Cystic Fibrosis Pulmonary Exacerbation Treatment

Rationale: Pulmonary exacerbations (PExs) are associated with significant morbidity in people with cystic fibrosis (CF). Severe PExs are treated with intravenous antibiotics, including tobramycin. CF care guidelines recommend continuing chronic maintenance medications during PEx treatment. Azithromycin (AZM) is one of the most widely prescribed chronic medications for CF in the United States. Recent evidence has identified a potential antagonistic relationship between AZM and tobramycin.Objectives: To determine whether, among PEx treated with intravenous tobramycin, concomitant AZM use is associated with worse clinical outcomes.Methods: Retrospective cohort study using the CF Foundation Patient Registry-Pediatric Health Information System (CFFPR-PHIS)-linked dataset. People with CF age 6-21 years were included if they were hospitalized between 2006 and 2016 for a PEx. Inverse probability of treatment weighing was used to minimize the effects of confounders, including indication bias. Associations of concomitant treatment with AZM and lung function outcomes were determined using linear mixed-effect models and generalized estimating equations. Cox proportional hazard regression models were used to evaluate associations with time to next PEx.Results: Among the 10,660 people with CF included in the CFFPR-PHIS-linked dataset, 2,294 children and adolescents with 5,022 PExs that had intravenous tobramycin use were identified. A little less than half (n = 2,247; 45%) of all PExs were treated concomitantly with AZM and intravenous tobramycin. AZM use both at the most recent outpatient clinic encounter and during PEx treatment in combination with intravenous tobramycin was associated with a significantly lower absolute improvement in percentage-predicted forced expiratory volume in 1 second (ppFEV₁) (-0.93%; 95% confidence interval [CI], -1.78 to -0.07; P = 0.033), a lesser odds of returning to 90% or more of baseline ppFEV₁ (odds ratio, 0.79; 95% CI, 0.68-0.93; P = 0.003), and a shorter time to next PEx requiring intravenous antibiotics (hazard ratio, 1.22; 95% CI, 1.14-1.31; P < 0.001) compared with intravenous tobramycin use without concomitant AZM.Conclusions: Concomitant AZM and intravenous tobramycin use for in-hospital PEx treatment was associated with poorer clinical outcomes than treatment with intravenous tobramycin without AZM. These results support the hypothesis that an antagonistic relationship between these two medications might exist.

Effects of Tigecycline Combined with Azithromycin Against Biofilms of Multidrug-Resistant Stenotrophomonas maltophilia Isolates from a Patient in China

Purpose

Our aim was to investigate in vitro biofilm formation by S. maltophilia and the effects of antibacterial agents used to prevent biofilm formation.

Methods

Two trimethoprim/sulfamethoxazole-resistant S. maltophilia strains were isolated from the pleural effusion of a patient with cancer. The minimum inhibitory concentrations (MICs) of amikacin, azithromycin, cefoperazone/sulbactam, and tigecycline were determined. The checkerboard method was used to determine the fractional inhibitory concentration indices (FICIs). A crystal violet biofilm assay and confocal laser scanning microscopy (CLSM) were used to observe biofilm formation. In vitro effects of azithromycin combined with tigecycline on biofilms of S. maltophilia strains were tested.

Results

The two S. maltophilia isolates were confirmed to produce strong biofilms. Crystal violet biofilm assay and CLSM analysis of S. maltophilia biofilm were in the initial adhesive stage after 2 h incubation. Biofilm was in the exponential phase of growth at 12 h and reached maximal growth at 36–48 h. Compared with tigecycline or azithromycin alone, the combination of tigecycline and azithromycin increased the inhibiting effect S. maltophilia biofilm biomass after incubation for 12 h. Compared with the control group, in almost all strains treated with tigecycline and azithromycin, the biofilm was significantly suppressed significance (P<0.001). We found that 2x MIC azithromycin combined with 1x MIC tigecycline had the best inhibiting effect against the biofilm, the biofilm inhibition rates of three strains were all over 60%, the biofilm thickness was inhibited from 36.00 ± 4.00 μm to 8.00 μm, from 40.00 μm to 6.67± 2.31 μm, and from 32.00 μm to 13.33 ± 2.31 μm in SMA1, SMA2 and ATCC17666, respectively.

Conclusion

Azithromycin combined with tigecycline inhibited biofilm formation by S. maltophilia. Our study provides an experimental basis for a possible optimal treatment strategy for S. maltophilia biofilm-related infections.

Evaluation of Combined Ciprofloxacin and azithromycin free and nano formulations to control biofilm producing Pseudomonas aeruginosa isolated from burn wounds

BACKGROUND

Nanoparticles are becoming increasingly important against resistant superbugs including Pseudomonas aeruginosa infections.

AIMS

Exploration of Azithromycin as an adjunctive therapy to Ciprofloxacin for treatment of P. aeruginosa infections. Also, preparation of Ciprofloxacin-Azithromycin nanoparticles on chitosan nanocarrier (Cipro-AZM-CS) and assessment of its antimicrobial effect in vitro and in vivo.

METHODS

Detection of biofilm production and biofilm-specific antibiotic resistance ndvB and tssC1 genes was attempted. Minimal inhibitory concentration (MIC) and Minimum biofilm eradication concentration (MBEC) were done in vitro for assessment of P. aeruginosa planktonic and biofilm forms eradication, respectively. In In vivo study, Cipro-AZM-CS and free form were used to evaluate survival rate, wound contraction and bacterial load in mice after third degree burn.

RESULTS

All isolates were positive for biofilm production and ndvB and tssC1 genes. Majority of isolates (37, 74%) were extensively drug resistant. In the planktonic state, MIC values of Cipro-AZM free and CS forms were significantly lower than free Cipro MIC (P = 0.015 and P < 0.001 respectively). Also, Cipro-AZM free and CS MBEC values were significantly lower than that of free Cipro (P < 0.010 and P < 0.001 respectively). Furthermore, The MIC and MBEC values of free Cipro-AZM decreased significantly when challenged with Cipro-AZM-CS (P = 0.009 and P < 0.001 respectively). In vivo study combined free and Cipro-AZM-CS treated subgroups showed 100% mice survival with early resolution of infection and wound contraction (75%, 77.5% respectively) VS 45% for Cipro CS (P < 0.001).

CONCLUSION

Combined free and Cipro-AZM-CS showed promising results in vitro and in vivo overcoming high resistance of biofilm producing P. aeruginosa.

Oral Azithromycin Use and the Recovery of Lung Function from Pulmonary Exacerbations Treated with Intravenous Tobramycin or Colistimethate in Adults with Cystic Fibrosis

Rationale: The potential of azithromycin to alter the antimicrobial and clinical benefits of inhaled tobramycin in patients with cystic fibrosis (CF) has been previously reported. The potential interaction between azithromycin and intravenous antibiotics in the treatment of pulmonary exacerbations is unknown. Objectives: To determine if chronic azithromycin use as a concomitant therapy is associated with change in lung function after receiving intravenous antibiotic regimens including tobramycin or colistimethate. Methods: This was a retrospective cohort study evaluating the association of azithromycin with intravenous tobramycin or colistimethate in adult patients with CF treated for a pulmonary exacerbation. The primary outcome was relative lung function recovery (forced expiratory volume in 1 s [FEV₁]) after exacerbation treatment. Generalized estimating equations were applied to account for repeated events with independent correlation structures and robust standard errors, incorporating several confounders. Results: A total of 220 exacerbation events occurred in 121 patients in the tobramycin group (47% using azithromycin), and 207 exacerbation events occurred in 86 patients in the colistimethate group (59% using azithromycin). Azithromycin use was associated with less FEV₁% recovery in patients treated with tobramycin (-3% relative FEV₁% recovery [95% confidence interval (CI), -7 to 0.2] and -2.64% absolute FEV₁% change [95% CI, -4.52 to -0.76]). Azithromycin use was associated with greater recovery of FEV₁% when treated with colistimethate (+3% relative FEV₁% recovery [95% CI, -0.1 to 7] and 2.00% absolute improvement in FEV₁% [95% CI, 0.13 to 3.87]). The odds of 90% or 100% recovery to baseline FEV₁% were lower with azithromycin use in the tobramycin cohort and higher with azithromycin use in the colistimethate cohort but were not statistically significant. Conclusions: Azithromycin use was associated with a more favorable response in adult patients with CF treated with intravenous colistimethate but a less favorable response in those treated with intravenous tobramycin.

Pulmonary Outcomes Associated with Long-Term Azithromycin Therapy in Cystic Fibrosis

Rationale: Chronic azithromycin is commonly used in cystic fibrosis based on short controlled clinical trials showing reductions in pulmonary exacerbations and improved FEV₁. Long-term effects are unknown.

Objectives: Examine pulmonary outcomes among chronic azithromycin users compared with matched controls over years of use and consider combined azithromycin use in cohorts using chronic inhaled tobramycin or aztreonam.

Methods: This retrospective cohort study used the U.S. cystic fibrosis Foundation Patient Registry. Incident chronic azithromycin users were compared with matched controls by FEV₁% predicted rate of decline and rates of intravenous antibiotic use to treat pulmonary exacerbations. Propensity score methods were utilized to address confounding by indication. Predefined sensitivity analyses based on lung function, Pseudomonas aeruginosa (PA) status, and follow-up time intervals were conducted.

Measurements and Main Results: Across 3 years, FEV₁% predicted per-year decline was nearly 40% less in those with PA using azithromycin compared with matched controls (slopes, −1.53 versus −2.41% predicted per yr; difference: 0.88; 95% confidence interval [CI], 0.30–1.47). This rate of decline did not differ based on azithromycin use in those without PA. Among all cohorts, use of intravenous antibiotics was no different between azithromycin users and controls. Users of inhaled tobramycin and azithromycin had FEV₁% predicted per-year decline of −0.16 versus nonusers (95% CI, −0.44 to 0.13), whereas users of inhaled aztreonam lysine and azithromycin experienced a mean 0.49% predicted per year slower decline than matched controls (95% CI, −0.11 to 1.10).

Conclusions: Results from this study provide additional rationale for chronic azithromycin use in PA-positive patients to reduce lung function decline.

Molecular Mechanisms of Phosphate Stress Activation of Pseudomonas aeruginosa Quorum Sensing Systems

It is not fully understood how phosphate deficiency could influence the virulence of Pseudomonas aeruginosa through modulation of the bacterial QS systems. This report presents a systemic investigation on the impact of phosphate depletion on the hierarchy of quorum sensing systems of P. aeruginosa. The results showed that phosphate stress could have an extensive impact on the QS networks of this bacterial pathogen. Among the 7 QS regulatory genes representing the 3 sets of QS systems tested, 4 were significantly upregulated by phosphate depletion stress through the PhoR/PhoB two-component regulatory system, especially the upstream QS regulatory gene lasI. We also present evidence that the response regulator PhoB was a strong competitor against the las regulators LasR and RsaL for the lasI promoter, unveiling the mechanistic basis of the process by which phosphate stress could modulate the bacterial QS systems.

The hierarchical quorum sensing (QS) systems of Pseudomonas aeruginosa, consisting of las, pqs, and rhl, coordinate the expression of bacterial virulence genes. Previous studies showed that under phosphate deficiency conditions, two-component regulatory system PhoRB could activate various genes involved in cytotoxicity through modulation of QS systems, but the mechanism by which PhoR/PhoB influences QS remains largely unknown. Here, we provide evidence that among the key QS regulatory genes in P. aeruginosa, rhlR, pqsA, mvfR, and lasI were activated by the response regulator PhoB under phosphate-depleted conditions. We show that PhoB is a strong competitor against LasR and RsaL for binding to the promoter of lasI and induces significant expression of lasI, rhlR, and mvfR. However, expression of lasI, encoding the signal 3-oxo-C12-HSL, was increased only marginally under the same phosphate-depleted conditions. This seeming inconsistency was attributed to the induction of pvdQ, which encodes an enzyme for degradation of 3-oxo-C12-HSL signal molecules. Taken together, the results from this study demonstrate that through the two-component regulatory system PhoR/PhoB, phosphate depletion stress could influence the QS network by modulating several key regulators, including lasI, rhlR, mvfR, and pvdQ. The findings highlight not only the potency of the PhoR/PhoB-mediated bacterial stress response mechanism but also the plasticity of the P. aeruginosa QS systems in coping with the changed environmental conditions.

IMPORTANCE It is not fully understood how phosphate deficiency could influence the virulence of Pseudomonas aeruginosa through modulation of the bacterial QS systems. This report presents a systemic investigation on the impact of phosphate depletion on the hierarchy of quorum sensing systems of P. aeruginosa. The results showed that phosphate stress could have an extensive impact on the QS networks of this bacterial pathogen. Among the 7 QS regulatory genes representing the 3 sets of QS systems tested, 4 were significantly upregulated by phosphate depletion stress through the PhoR/PhoB two-component regulatory system, especially the upstream QS regulatory gene lasI. We also present evidence that the response regulator PhoB was a strong competitor against the las regulators LasR and RsaL for the lasI promoter, unveiling the mechanistic basis of the process by which phosphate stress could modulate the bacterial QS systems.

Polymeric Composites with Silver (I) Cyanoximates Inhibit Biofilm Formation of Gram-Positive and Gram-Negative Bacteria

Biofilms are surface-associated microbial communities known for their increased resistance to antimicrobials and host factors. This resistance introduces a critical clinical challenge, particularly in cases associated with implants increasing the predisposition for bacterial infections. Preventing such infections requires the development of novel antimicrobials or compounds that enhance bactericidal effect of currently available antibiotics. We have synthesized and characterized twelve novel silver(I) cyanoximates designated as Ag(ACO), Ag(BCO), Ag(CCO), Ag(ECO), Ag(PiCO), Ag(PICO) (yellow and red polymorphs), Ag(BIHCO), Ag(BIMCO), Ag(BOCO), Ag(BTCO), Ag(MCO) and Ag(PiPCO). The compounds exhibit a remarkable resistance to high intensity visible light, UV radiation and heat and have poor solubility in water. All these compounds can be well incorporated into the light-curable acrylate polymeric composites that are currently used as dental fillers or adhesives of indwelling medical devices. A range of dry weight % from 0.5 to 5.0 of the compounds was tested in this study. To study the potential of these compounds in preventing planktonic and biofilm growth of bacteria, we selected two human pathogens (Gram-negative Pseudomonas aeruginosa and Gram-positive Staphylococcus aureus) and Gram-positive environmental isolate Bacillus aryabhattai. Both planktonic and biofilm growth was abolished completely in the presence of 0.5% to 5% of the compounds. The most efficient inhibition was shown by Ag(PiCO), Ag(BIHCO) and Ag(BTCO). The inhibition of biofilm growth by Ag(PiCO)-yellow was confirmed by scanning electron microscopy (SEM). Application of Ag(BTCO) and Ag(PiCO)-red in combination with tobramycin, the antibiotic commonly used to treat P. aeruginosa infections, showed a significant synergistic effect. Finally, the inhibitory effect lasted for at least 120 h in P. aeruginosa and 36 h in S. aureus and B. aryabhattai. Overall, several silver(I) cyanoximates complexes efficiently prevent biofilm development of both Gram-negative and Gram-positive bacteria and present a particularly significant potential for applications against P. aeruginosa infections.

Inflammation in cystic fibrosis: An update

Inflammation plays a critical role in cystic fibrosis (CF) lung pathology and disease progression making it an active area of research and important therapeutic target. In this review, we explore the most recent research on the major contributors to the exuberant inflammatory response seen in CF as well as potential therapeutics to combat this response. Absence of functional cystic fibrosis transmembrane conductance regulator (CFTR) alters anion transport across CF airway epithelial cells and ultimately results in dehydration of the airway surface liquid. The dehydrated airway surface liquid in combination with abnormal mucin secretion contributes to airway obstruction and subsequent infection that may serve as a trigger point for inflammation. There is also evidence to suggest that airway inflammation may be excessive and sustained relative to the infectious stimuli. Studies have shown dysregulation of both pro-inflammatory mediators such as IL-17 and pro-resolution mediators including metabolites of the eicosanoid pathway. Recently, CFTR potentiators and correctors have garnered much attention in the CF community. Although these modulators address the underlying defect in CF, their impact on downstream consequences such as inflammation are not known. Here, we review pre-clinical and clinical data on the impact of CFTR modulators on inflammation. In addition, we examine other cell types including neutrophils, macrophages, and T-lymphocytes that express CFTR and contribute to the CF inflammatory response. Finally, we address challenges in developing anti-inflammatory therapies and highlight some of the most promising anti-inflammatory drugs under development for CF.

Recent advances on topical antimicrobials for skin and soft tissue infections and their safety concerns

Antimicrobial resistance of disease-related microorganisms is considered a worldwide prevalent and serious issue which increases the failure of treatment outcomes and leads to high mortality. Considering that the increased resistance to systemic antimicrobial therapy often needs of the use of more toxic agents, topical antimicrobial therapy emerges as an attractive route for the treatment of infectious diseases. The topical antimicrobial therapy is based on the absorption of high drug doses in a readily accessible skin surface, resulting in a reduction of microbial proliferation at infected skin sites. Topical antimicrobials retain the following features: (a) they are able to escape the enzymatic degradation and rapid clearance in the gastrointestinal tract or the first-pass metabolism during oral administration; (b) alleviate the physical discomfort related to intravenous injection; (c) reduce possible adverse effects and drug interactions of systemic administrations; (d) increase patient compliance and convenience; and (e) reduce the treatment costs. Novel antimicrobials for topical application have been widely exploited to control the emergence of drug-resistant microorganisms. This review provides a description of antimicrobial resistance, common microorganisms causing skin and soft tissue infections, topical delivery route of antimicrobials, safety concerns of topical antimicrobials, recent advances, challenges and future prospective in topical antimicrobial development.

Impact of azithromycin on the clinical and antimicrobial effectiveness of tobramycin in the treatment of cystic fibrosis

BACKGROUND

Concomitant use of oral azithromycin and inhaled tobramycin occurs in approximately half of US cystic fibrosis (CF) patients. Recent data suggest that this combination may be antagonistic.

METHODS

Test the hypothesis that azithromycin reduces the clinical benefits of tobramycin by analyses of clinical trial data, in vitro modeling of P. aeruginosa antibiotic killing, and regulation of the MexXY efflux pump.

RESULTS

Ongoing administration of azithromycin associates with reduced ability of inhaled tobramycin, as compared with aztreonam, to improve lung function and quality of life in a completed clinical trial. In users of azithromycin FEV₁ (L) increased 0.8% during a 4-week period of inhaled tobramycin and an additional 6.4% during a subsequent 4-week period of inhaled aztreonam (P<0.005). CFQ-R respiratory symptom score decreased 1.8 points during inhaled tobramycin and increased 8.3 points during subsequent inhaled aztreonam (P<0.001). A smaller number of trial participants not using azithromycin had similar improvement in lung function and quality of life scores during inhaled tobramycin and inhaled aztreonam. In vitro, azithromycin selectively reduced the bactericidal effects tobramycin in cultures of clinical strains of P. aeruginosa, while up regulating antibiotic resistance through MexXY efflux.

CONCLUSIONS

Azithromycin appears capable of reducing the antimicrobial benefits of tobramycin by inducing adaptive bacterial stress responses in P. aeruginosa, suggesting that these medications together may not be optimal chronic therapy for at least some patients.

Effects of Fluoroquinolones and Azithromycin on Biofilm Formation of Stenotrophomonas maltophilia

Stenotrophomonas maltophilia is an opportunistic pathogen that causes respiratory and urinary tract infections, as well as wound infections in immunocompromised patients. This pathogen is difficult to treat due to increased resistance to many antimicrobial agents. We investigated the in vitro biofilm formation of S. maltophilia, including effects of fluoroquinolones (FQs) and azithromycin on biofilm formation. The organism initiated attachment to polystyrene surfaces after a 4 h incubation period, and reached maximal growth at 18–24 h. In the presence of FQs (moxifloxacin, levofloxacin or ciprofloxacin), the biofilm biomass was significantly reduced (P < 0.05). A lower concentration of moxifloxacin (10 μg/mL) exhibited a better inhibiting effect on biofilm formation than 100 μg/mL (P < 0.01), but with no difference in effect compared to the 50 μg/mL concentration (P > 0.05). However, the inhibitory effects of 10 μg/mL of levofloxacin or ciprofloxacin were slightly less pronounced than those of the higher concentrations. A combination of azithromycin and FQs significantly reduced the biofilm inhibiting effect on S. maltophilia preformed biofilms compared to azithromycin or FQs alone. We conclude that early use of clinically acceptable concentrations of FQs, especially moxifloxacin (10 μg/mL), may possibly inhibit biofilm formation by S. maltophilia. Our study provides an experimental basis for a possible optimal treatment strategy for S. maltophilia biofilm-related infections.

Drug interactions and treatment burden as survival improves

PURPOSE OF REVIEW

With our growing understanding of the pathophysiology of cystic fibrosis, the pace of drug discovery is accelerating. Newer agents and therapies have traditionally been added to available medications, given the urgency in treating the disease. As the cystic fibrosis population ages, the number of associated comorbidities increases, requiring additional therapeutic approaches. Thus, while current management strategies have dramatically extended projected life expectancy, the treatment burden of the disease in adulthood has become onerous, and there is increasing concern over unintended effects and drug-drug interactions of new and existing therapies.

RECENT FINDINGS

A number of recent studies have sought to quantify the treatment burden of cystic fibrosis care, and to identify ways to reduce this burden. Mechanistic studies have identified the potential for a number of cystic fibrosis medications to impair the host response, or to interfere with the efficacy of other agents.

SUMMARY

As the cystic fibrosis formulary grows, a primary emphasis will be for providers to develop personalized treatment plans, with a goal to reduce unnecessary treatment burden and an awareness of potential unanticipated effects of medications.

Fabrication of a Selective and Sensitive Sensor Based on Molecularly Imprinted Polymer/Acetylene Black for the Determination of Azithromycin in Pharmaceuticals and Biological Samples

A new selective and sensitive sensor based on molecularly imprinted polymer/acetylene black (MIP/AB) was developed for the determination of azithromycin (AZM) in pharmaceuticals and biological samples. The MIP of AZM was synthesized by precipitation polymerization. MIP and AB were then respectively introduced as selective and sensitive elements for the preparation of MIP/AB-modified carbon paste (MIP/ABP) electrode. The performance of the obtained sensor was estimated by cyclic voltammetry (CV) and differential pulse voltammetry (DPV) techniques. Compared with non-molecularly imprinted polymer (NIP) electrodes, NIP/ABP electrodes, and MIP-modified carbon paste electrodes, MIP/ABP electrode exhibited excellent current response toward AZM. The prepared sensor also exhibited good selectivity for AZM in comparison with structurally similar compounds. The effect of electrode composition, extraction parameters, and electrolyte conditions on the current response of the sensor was investigated. Under the optimized conditions, the prepared sensor showed two dynamic linear ranges of 1.0 × 10⁻⁷ mol L⁻¹ to 2.0 × 10⁻⁶ mol L⁻¹ and 2.0 × 10⁻⁶ mol L⁻¹ to 2.0 × 10⁻⁵ mol L⁻¹, with a limit of detection of 1.1 × 10⁻⁸ mol L⁻¹. These predominant properties ensured that the sensor exhibits excellent reliability for detecting AZM in pharmaceuticals and biological fluids without the assistance of any separation techniques. The results were validated by the high-performance liquid chromatography–tandem mass spectrometry method.

Effects of phosphate supplementation on Pseudomonas aeruginosa invasive behavior in burn wound infections: A simple approach to a big problem

This study was designed to investigate the effect of inorganic phosphate supplementation on invasive behavior of Pseudomonas aeruginosa in burn wound infections. An emulsion-based lotion containing sodium dihydrogen phosphate was formulated and then 50 female Sprague-Dawley rats with burn wounds were used to assess the effect of phosphate supplementation on swarming motility of P. aeruginosa. On the second day after burn, four groups of rats were inoculated with P. aeruginosa and one group was left as negative control. The treatment was started on day 3 and the animals were followed up for 4 weeks. Significant improvement in wound healing was observed in the phosphate-receiving group after the 4-week follow-up, compared to the negative control, positive control, and silver sulfadiazine-receiving groups. Histopathological assessment of the tissue samples also indicated the healing process in phosphate-enriched lotion receiving group. The results showed that inorganic phosphate supplementation results in alteration of the virulence behavior of P. aeruginosa and improvement in the wound healing process. In conclusion, phosphate supplementation would be a rational strategy in the eradication of P. aeruginosa wound infection.

Recombinant outer membrane protein F-B subunit of LT protein as a prophylactic measure against Pseudomonas aeruginosa burn infection in mice

AIM: To study immunogenicity of outer membrane protein F (OprF) fused with B subunit of LT (LTB), against Pseudomonas aeruginosa (P. aeruginosa).

METHODS: The OprF, a major surface exposed outer membrane protein that is antigenically conserved in various strains of P. aeruginosa, is a promising immunogen against P. aeruginosa. In the present study recombinant OprF and OprF-LTB fusion gene was cloned, expressed and purified. BALB/c mice and rabbits were immunized using recombinant OprF and OprF-LTB and challenged at the burn site with P. aeruginosa lethal dose of 10⁴ CFU. The protective efficacy of rabbit anti OprF IgG against P. aeruginosa burn infection was investigated by passive immunization.

RESULTS: It has been well established that the LTB is a powerful immunomodulator with strong adjuvant activity. LTB as a bacterial adjuvant enhanced immunogenicity of OprF and anti OprF IgG titer in serum was increased. Experimental findings showed significantly higher average survival rate in burned mice immunized with OprF-LTB than immunized with OprF or the control group. Rabbits anti OprF IgG brought about 75% survival of mice following challenge with P. aeruginosa. Post challenge hepatic and splenic tissues of mice group immunized with OprF-LTB had significantly lower bacterial load than those immunized with OprF or the control groups.

CONCLUSION: These results demonstrate that LTB-fused OprF might be a potential candidate protein for a prophylactic measure against P. aeruginosa in burn infection.

Selection of Single-Stranded DNA Molecular Recognition Elements against Exotoxin A Using a Novel Decoy-SELEX Method and Sensitive Detection of Exotoxin A in Human Serum

Exotoxin A is one of the virulence factors of Pseudomonas aeruginosa, a bacterium that can cause infections resulting in adverse health outcomes and increased burden to health care systems. Current methods of diagnosing P. aeruginosa infections are time consuming and can require significant preparation of patient samples. This study utilized a novel variation of the Systematic Evolution of Ligand by Exponential Enrichment, Decoy-SELEX, to identify an Exotoxin A specific single-stranded DNA (ssDNA) molecular recognition element (MRE). Its emphasis is on increasing stringency in directing binding toward free target of interest and at the same time decreasing binding toward negative targets. A ssDNA MRE with specificity and affinity was identified after fourteen rounds of Decoy-SELEX. Utilizing surface plasmon resonance measurements, the determined equilibrium dissociation constant (K_d) of the MRE is between 4.2 µM and 4.5 µM, and is highly selective for Exotoxin A over negative targets. A ssDNA MRE modified sandwich enzyme-linked immunosorbent assay (ELISA) has been developed and achieved sensitive detection of Exotoxin A at nanomolar concentrations in human serum. This study has demonstrated the proof-of-principle of using a ssDNA MRE as a clinical diagnostic tool.

Tobramycin inhalation powder: an efficient and efficacious therapy for the treatment of Pseudomonas aeruginosa infection in cystic fibrosis

Inhaled antipseudomonal therapies are critical components in the management of cystic fibrosis (CF) and have significantly contributed to improved patient outcomes. Dry powder inhaler technologies represent a significant advance in drug delivery, alleviating treatment burden and potentially improving adherence associated with traditional CF nebulized therapies. Tobramycin inhalation powder (TIP) uses PulmoSphere® technology for very efficient drug delivery into the lower airways. In placebo-controlled and comparative studies with traditional tobramycin formulations, TIP is equally efficacious and is associated with increased patient convenience and satisfaction. TIP has been recommended in the 2013 CF Foundation and the 2014 European guidelines as a therapy in CF for the maintenance of lung health. Going forward, TIP may offer a therapeutic advantage over traditional formulations of tobramycin as recent prospective ‘real world’ studies of TIP have demonstrated high patient tolerance and improved adherence compared with traditional formulations.

Azithromycin may antagonize inhaled tobramycin when targeting Pseudomonas aeruginosa in cystic fibrosis

RATIONALE

Recent studies of inhaled tobramycin in subjects with cystic fibrosis (CF) find less clinical improvement than previously observed. Nonhuman data suggest that in some strains of Pseudomonas aeruginosa, azithromycin can antagonize tobramycin.

OBJECTIVES

We tested the hypothesis that concomitant azithromycin use correlates with less improvement in key outcome measures in subjects receiving inhaled tobramycin while not affecting those receiving a comparative, nonaminoglycoside inhaled antibiotic.

METHODS

We studied a cohort of 263 subjects with CF enrolled in a recent clinical trial comparing inhaled tobramycin with aztreonam lysine. We performed a secondary analysis to examine key clinical and microbiologic outcomes based on concomitant, chronic azithromycin use at enrollment.

MEASUREMENTS AND MAIN RESULTS

The cohort randomized to inhaled tobramycin and reporting azithromycin use showed a significant decrease in the percent predicted FEV1 after one and three courses of inhaled tobramycin when compared with those not reporting azithromycin use (28 d: -0.51 vs. 3.43%, P < 0.01; 140 d: -1.87 vs. 6.07%, P < 0.01). Combined azithromycin and inhaled tobramycin use was also associated with earlier need for additional antibiotics, lesser improvement in disease-related quality of life, and a trend toward less reduction in sputum P. aeruginosa density. Subjects randomized to inhaled aztreonam lysine had significantly greater improvement in these outcome measures, which were unaffected by concomitant azithromycin use. Outcomes in those not using azithromycin who received inhaled tobramycin were not significantly different from subjects receiving aztreonam lysine. Azithromycin also antagonized tobramycin but not aztreonam lysine in 40% of P. aeruginosa clinical isolates tested in vitro.

CONCLUSIONS

Oral azithromycin may antagonize the therapeutic benefits of inhaled tobramycin in subjects with CF with P. aeruginosa airway infection.

Enhanced in vitro formation and antibiotic resistance of nonattached Pseudomonas aeruginosa aggregates through incorporation of neutrophil products

Pseudomonas aeruginosa is a major pathogen in cystic fibrosis (CF) lung disease. Children with CF are routinely exposed to P. aeruginosa from the natural environment, and by adulthood, 80% of patients are chronically infected. P. aeruginosa in the CF airway exhibits a unique biofilm-like structure, where it grows in small clusters or aggregates of bacteria in association with abundant polymers of neutrophil-derived components F-actin and DNA, among other components. These aggregates differ substantially in size and appearance compared to surface-attached in vitro biofilm models classically utilized for studies but are believed to share properties of surface-attached biofilms, including antibiotic resistance. However, little is known about the formation and function of surface-independent modes of biofilm growth, how they might be eradicated, and quorum sensing communication. To address these issues, we developed a novel in vitro model of P. aeruginosa aggregates incorporating human neutrophil-derived products. Aggregates grown in vitro and those found in CF patients' sputum samples were morphologically similar; viable bacteria were distributed in small pockets throughout the aggregate. The lasA quorum sensing gene was differentially expressed in the presence of neutrophil products. Importantly, aggregates formed in the presence of neutrophils acquired resistance to tobramycin, which was lost when the aggregates were dispersed with DNase, and antagonism of tobramycin and azithromycin was observed. This novel yet simple in vitro system advances our ability to model infection of the CF airway and will be an important tool to study virulence and test alternative eradication strategies against P. aeruginosa.

Pseudomonas aeruginosa elastase disrupts the cortisol-binding activity of corticosteroid-binding globulin

The serine protease inhibitor (SERPIN) family member corticosteroid-binding globulin (CBG) is the main carrier of glucocorticoids in plasma. Human CBG mediates the targeted release of cortisol at sites of inflammation through cleavage of its reactive center loop (RCL) by neutrophil elastase. The RCLs of SERPIN family members are targeted by diverse endogenous and exogenous proteases, including several bacterial proteases. We tested different bacteria for their ability to secrete proteases that disrupt CBG cortisol-binding activity, and characterized the responsible protease and site of CBG cleavage. Serum CBG integrity was assessed by Western blotting and cortisol-binding capacity assay. Effects of time, pH, temperature, and protease inhibitors were tested. Proteolytically active proteins from bacterial media were purified by fast protein liquid chromatography, and the active protease and CBG cleavage sites were identified by mass spectrometry. Among the bacteria tested, medium from Pseudomonas aeruginosa actively disrupted the cortisol-binding activity of CBG. This proteolytic activity was inhibited by zinc chelators and occurred most efficiently at pH 7 and elevated physiological temperature (ie, 41°C). Mass spectrometric analysis of a semi-purified fraction of P. aeruginosa media identified the virulence factor LasB as the responsible protease, and this was confirmed by assaying media from LasB-deficient P. aeruginosa. This metalloprotease cleaves the CBG RCL at a major site, distinct from that targeted by neutrophil elastase. Our results suggest that humoral responses to P. aeruginosa infection are influenced by this pathogen's ability to secrete a protease that promotes the release of the anti-inflammatory steroid, cortisol, from its plasma transport protein.