Antibiotic therapy against Pseudomonas aeruginosa in cystic fibrosis

[CF Lung Disease - a German S3 Guideline: Pseudomonas aeruginosa]

Cystic Fibrosis (CF) is the most common autosomal recessive genetic multisystemic disease. In Germany, it affects at least 8000 people. The disease is caused by mutations in the Cystic Fibrosis Transmembrane Conductance Regulator (CFTR) gene leading to dysfunction of CFTR, a transmembrane chloride channel. This defect causes insufficient hydration of the airway epithelial lining fluid which leads to reduction of the mucociliary clearance.Even if highly effective, CFTR modulator therapy has been available for some years and people with CF are getting much older than before, recurrent and chronic infections of the airways as well as pulmonary exacerbations still occur. In adult CF life, Pseudomonas aeruginosa (PA) is the most relevant pathogen in colonisation and chronic infection of the lung, leading to further loss of lung function. There are many possibilities to treat PA-infection.This is a S3-clinical guideline which implements a definition for chronic PA-infection and demonstrates evidence-based diagnostic methods and medical treatment in order to give guidance for individual treatment options.

Gene-Gene Interactions Reduce Aminoglycoside Susceptibility of Pseudomonas aeruginosa through Efflux Pump-Dependent and -Independent Mechanisms

Pseudomonas aeruginosa causes a wide range of acute and chronic infections. Aminoglycosides are a cornerstone of treatment, but isolates are often resistant. The purpose of this research was to better understand the genetic basis of aminoglycoside resistance in P. aeruginosa. Bioinformatic approaches identified mutations in resistance-associated genes in the clinical isolates of P. aeruginosa. The common mutations were then engineered into the genome of P. aeruginosa reference strain PAO1. Mutations in the elongation factor gene fusA1 caused the biggest reduction in aminoglycoside susceptibility, with mutations in the two-component regulator gene amgS and the efflux pump regulator gene mexZ having less impact. This susceptibility was further reduced by combinations of mutations. Mutations in fusA1, amgS and mexZ all increased the expression of the mexXY efflux pump that is strongly associated with aminoglycoside resistance. Furthermore, the fusA1 amgS mexZ triple mutant had the highest efflux pump gene expression. Engineering fusA1 and amgS mutants lacking this efflux pump showed that fusA1 and amgS also reduce aminoglycoside susceptibility through additional mechanisms. The fusA1 and amgS mutations reduced bacterial growth, showing that these mutations have a fitness cost. Our findings demonstrate the complex interplay between mutations, efflux pump expression and other mechanisms for reducing the susceptibility of P. aeruginosa to aminoglycosides.

Protective role of biogenic selenium nanoparticles in immunological and oxidative stress generated by enrofloxacin in broiler chicken

Presently most bacteria are becoming antibiotic resistant. Due to this there is a deficiency of potent antibiotics, therefore we have to preserve and improve the efficiency of existing antibiotics by mitigating the side effects. Enrofloxacin (EFX) is an important antimicrobial used in veterinary practice but it is known to exert immune suppression antioxidant stress. In the present study, we report on: (a) the biosynthesis of selenium nanoparticles (Se NPs), and (b) their protective effect in reducing adverse effects of EFX on broiler chicken. A potent bacterial strain, isolated from farm soil, has been identified as Pantoea agglomerans (GenBank: KU500622). It tolerates a high concentration of selenium dioxide (9 mM) and produces Se NPs under aerobic conditions. The obtained Se NPs are amorphous in structure and spherical in shape with sizes of less than 100 nm. The activity of cellular, humoral immune response and enzymatic and non-enzymatic antioxidants, has significantly been decreased as a result of EFX treatment. We investigated that Se NP supplementation greatly restores these values towards the control, and to even higher than those of the control. Adverse effects of EFX are prevented by simultaneous exposure to Se NPs (0.6 mg per kg of feed) in the diet of poultry chicken.

Intravenous combined with aerosolised polymyxin versus intravenous polymyxin alone in the treatment of pneumonia caused by multidrug-resistant pathogens: a systematic review and meta-analysis

Colistin has been used to treat nosocomial pneumonia (NP) caused by multidrug-resistant (MDR) Gram-negative bacteria (GNB) via different administration routes. Whether patients may benefit from aerosolised colistin as adjunctive treatment was contradictory. We aimed to clarify the safety and efficacy of administering aerosolised and intravenous (IV-AS) colistin versus intravenous (IV) colistin alone in patients with NP caused by MDR-GNB. Two reviewers independently evaluated and extracted data from PubMed, EMBASE and Cochrane databases. Primary outcomes were clinical response rate, all-cause mortality (ICU or hospital), microbiological eradication and nephrotoxicity. Pooled odds ratios (ORs) were calculated and significance was determined by the Z test. Nine eligible studies involving 672 participants were included. The overall clinical response rate (improvement and cure) was significantly higher in the IV-AS group than that in the IV group [OR=1.81, 95% confidence interval (CI) 1.30-2.53; P=0.0005]. Patients treated with IV-AS colistin showed a higher rate of pathogen eradication (OR=1.66, 95% CI 1.11-2.49; P=0.01) and lower all-cause mortality compared with IV colistin (OR=0.69, 95% CI 0.50-0.95; P=0.02). Nephrotoxicity did not differ significantly between IV-AS and IV groups (five studies; 383 patients) (OR=1.11, 95% CI 0.69-1.80; P=0.67). These data indicate that IV-AS colistin has additional benefits compared with IV colistin alone. Clinicians should be encouraged to give combined administration routes in critically ill patients with NP caused by MDR-GNB.

Delicate Metabolic Control and Coordinated Stress Response Critically Determine Antifungal Tolerance of Candida albicans Biofilm Persisters

Candida infection has emerged as a critical health care burden worldwide, owing to the formation of robust biofilms against common antifungals. Recent evidence shows that multidrug-tolerant persisters critically account for biofilm recalcitrance, but their underlying biological mechanisms are poorly understood. Here, we first investigated the phenotypic characteristics of Candida biofilm persisters under consecutive harsh treatments of amphotericin B. The prolonged treatments effectively killed the majority of the cells of biofilms derived from representative strains of Candida albicans, Candida glabrata, and Candida tropicalis but failed to eradicate a small fraction of persisters. Next, we explored the tolerance mechanisms of the persisters through an investigation of the proteomic profiles of C. albicans biofilm persister fractions by liquid chromatography-tandem mass spectrometry. The C. albicans biofilm persisters displayed a specific proteomic signature, with an array of 205 differentially expressed proteins. The crucial enzymes involved in glycolysis, the tricarboxylic acid cycle, and protein synthesis were markedly downregulated, indicating that major metabolic activities are subdued in the persisters. It is noteworthy that certain metabolic pathways, such as the glyoxylate cycle, were able to be activated with significantly increased levels of isocitrate lyase and malate synthase. Moreover, a number of important proteins responsible for Candida growth, virulence, and the stress response were greatly upregulated. Interestingly, the persisters were tolerant to oxidative stress, despite highly induced intracellular superoxide. The current findings suggest that delicate metabolic control and a coordinated stress response may play a crucial role in mediating the survival and antifungal tolerance of Candida biofilm persisters.

Structural basis for substrate specificity in ArnB. A key enzyme in the polymyxin resistance pathway of Gram-negative bacteria

Cationic Antimicrobial Peptides (CAMPs) represent a first line of defense against bacterial colonization. When fighting Gram-negative bacteria, CAMPs initially interact electrostatically with the negatively charged phosphate groups in lipid A and are thought to kill bacteria by disrupting their membrane integrity. However, many human pathogens, including Salmonella and Pseudomonas, have evolved lipid A modification mechanisms that result in resistance to CAMPs and related antibiotics such as Colistin. The addition of 4-amino-4-deoxy-l-Arabinose (Ara4N) to a phosphate group in lipid A is one such modification, frequently found in Pseudomonas isolated from cystic fibrosis patients. The pathway for biosynthesis of Ara4N-lipid A requires conversion of UDP-Glucuronic acid into UDP-Ara4N and subsequent transfer of the amino-sugar to lipid A. ArnB is a pyridoxal-phosphate (PLP) dependent transaminase that catalyzes a crucial step in the pathway: synthesis of UDP-Ara4N from UDP-4-keto-pentose. Here we present the 2.3 Å resolution crystal structure of an active site mutant of ArnB (K188A) in complex with the reaction intermediate aldimine formed by UDP-Ara4N and PLP. The sugar–nucleotide binding site is in a cleft between the subunits of the ArnB dimer with the uracil buried at the interface and the UDP ribose and phosphate groups exposed to the solvent. The Ara4N moiety is found in the ⁴C₁ conformation and its positioning, stabilized by interactions with both the protein and cofactor, is compatible with catalysis. The structure suggests strategies for the development of specific inhibitors that may prove useful in the treatment of resistant bacteria such as Pseudomonas found in cystic fibrosis patients.

Determinants of intrinsic aminoglycoside resistance in Pseudomonas aeruginosa

Screening of a transposon insertion mutant library of Pseudomonas aeruginosa for increased susceptibility to paromomycin identified a number of genes whose disruption enhanced susceptibility of this organism to multiple aminoglycosides, including tobramycin, amikacin, and gentamicin. These included genes associated with lipid biosynthesis or metabolism (lptA, faoA), phosphate uptake (pstB), and two-component regulators (amgRS, PA2797-PA2798) and a gene of unknown function (PA0392). Deletion mutants lacking these showed enhanced panaminoglycoside susceptibility that was reversed by the cloned genes, confirming their contribution to intrinsic panaminoglycoside resistance. None of these mutants showed increased aminoglycoside permeation of the cell envelope, indicating that increased susceptibility was not related to enhanced aminoglycoside uptake owing to a reduced envelope barrier function. Several mutants (pstB, faoA, PA0392, amgR) did, however, show increased cytoplasmic membrane depolarization relative to wild type following gentamicin exposure, consistent with the membranes of these mutants being more prone to perturbation, likely by gentamicin-generated mistranslated polypeptides. Mutants lacking any two of these resistance genes in various combinations invariably showed increased aminoglycoside susceptibility relative to single-deletion mutants, confirming their independent contribution to resistance and highlighting the complexity of the intrinsic aminoglycoside resistome in P. aeruginosa. Deletion of these genes also compromised the high-level panaminoglycoside resistance of clinical isolates, emphasizing their important contribution to acquired resistance.

Inhibition of growth of highly resistant bacterial and fungal pathogens by a natural product

The continuous escalation of resistant bacteria against a wide range of antibiotics necessitates discovering novel unconventional sources of antibiotics. B. oleracea L (red cabbage) is health-promoting food with proven anticancer and anti-inflammatory activities. However, it has not been researched adequately for its antimicrobial activity on potential resistant pathogens. The methanol crude extract of B. oleracea L. was investigated for a possible anti-microbial activity. The screening method was conducted using disc diffusion assay against 22 pathogenic bacteria and fungi. It was followed by evaluation of the minimum inhibitory concentration (MIC). Moreover, the antibacterial and the antifungal activities were confirmed using the minimum bactericidal concentration (MBC) and the minimum fungicidal concentration (MFC), respectively. Remarkable, antibacterial activity was evident particularly against highly infectious microorganisms such as Methicillin-resistant Staphylococcus aureus, Escherichia coli O157:H7, Pseudomonas aeruginosa, Klebsiella pneumoniae, Staphylococcus aureus, and Salmonella enterica serovar Typhimurium as well as against human fungal pathogens, Trichophyton rubrum and Aspergillus terreus. Red cabbage is a rich source of phenolic compounds, anthocyanins being the most abundant class, which might explain its potent antimicrobial action. This extract is potentially novel for future antimicrobials, inexpensive, and readily available at a large scale for pharmaceutical companies for further investigation and processing.

Pseudomonas aeruginosa: resistance to the max

Pseudomonas aeruginosa is intrinsically resistant to a variety of antimicrobials and can develop resistance during anti-pseudomonal chemotherapy both of which compromise treatment of infections caused by this organism. Resistance to multiple classes of antimicrobials (multidrug resistance) in particular is increasingly common in P. aeruginosa, with a number of reports of pan-resistant isolates treatable with a single agent, colistin. Acquired resistance in this organism is multifactorial and attributable to chromosomal mutations and the acquisition of resistance genes via horizontal gene transfer. Mutational changes impacting resistance include upregulation of multidrug efflux systems to promote antimicrobial expulsion, derepression of ampC, AmpC alterations that expand the enzyme's substrate specificity (i.e., extended-spectrum AmpC), alterations to outer membrane permeability to limit antimicrobial entry and alterations to antimicrobial targets. Acquired mechanisms contributing to resistance in P. aeruginosa include β-lactamases, notably the extended-spectrum β-lactamases and the carbapenemases that hydrolyze most β-lactams, aminoglycoside-modifying enzymes, and 16S rRNA methylases that provide high-level pan-aminoglycoside resistance. The organism's propensity to grow in vivo as antimicrobial-tolerant biofilms and the occurrence of hypermutator strains that yield antimicrobial resistant mutants at higher frequency also compromise anti-pseudomonal chemotherapy. With limited therapeutic options and increasing resistance will the untreatable P. aeruginosa infection soon be upon us?

Pseudomonas aeruginosa: resistance to the max

Pseudomonas aeruginosa is intrinsically resistant to a variety of antimicrobials and can develop resistance during anti-pseudomonal chemotherapy both of which compromise treatment of infections caused by this organism. Resistance to multiple classes of antimicrobials (multidrug resistance) in particular is increasingly common in P. aeruginosa, with a number of reports of pan-resistant isolates treatable with a single agent, colistin. Acquired resistance in this organism is multifactorial and attributable to chromosomal mutations and the acquisition of resistance genes via horizontal gene transfer. Mutational changes impacting resistance include upregulation of multidrug efflux systems to promote antimicrobial expulsion, derepression of ampC, AmpC alterations that expand the enzyme's substrate specificity (i.e., extended-spectrum AmpC), alterations to outer membrane permeability to limit antimicrobial entry and alterations to antimicrobial targets. Acquired mechanisms contributing to resistance in P. aeruginosa include β-lactamases, notably the extended-spectrum β-lactamases and the carbapenemases that hydrolyze most β-lactams, aminoglycoside-modifying enzymes, and 16S rRNA methylases that provide high-level pan-aminoglycoside resistance. The organism's propensity to grow in vivo as antimicrobial-tolerant biofilms and the occurrence of hypermutator strains that yield antimicrobial resistant mutants at higher frequency also compromise anti-pseudomonal chemotherapy. With limited therapeutic options and increasing resistance will the untreatable P. aeruginosa infection soon be upon us?

Oxidative stress induction of the MexXY multidrug efflux genes and promotion of aminoglycoside resistance development in Pseudomonas aeruginosa

Exposure to reactive oxygen species (ROS) (e.g., peroxide) was shown to induce expression of the PA5471 gene, which was previously shown to be required for antimicrobial induction of the MexXY components of the MexXY-OprM multidrug efflux system and aminoglycoside resistance determinant in Pseudomonas aeruginosa. mexXY was also induced by peroxide exposure, and this too was PA5471 dependent. The prospect of ROS promoting mexXY expression and aminoglycoside resistance recalls P. aeruginosa infection of the chronically inflamed lungs of cystic fibrosis (CF) patients, where the organism is exposed to ROS and where MexXY-OprM predominates as the mechanism of aminoglycoside resistance. While ROS did not enhance aminoglycoside resistance in vitro, long-term (8-day) exposure of P. aeruginosa to peroxide (mimicking chronic in vivo ROS exposure) increased aminoglycoside resistance frequency, dependent upon PA5471 and mexXY. This enhanced resistance frequency was also seen in a mutant strain overexpressing PA5471, in the absence of peroxide, suggesting that induction of PA5471 by peroxide was key to peroxide enhancement of aminoglycoside resistance frequency. Resistant mutants selected following peroxide exposure were typically pan-aminoglycoside-resistant, with mexXY generally required for this resistance. Moreover, PA5471 was required for mexXY expression and aminoglycoside resistance in these as well as several CF isolates examined.

Genetic determinants involved in the susceptibility of Pseudomonas aeruginosa to beta-lactam antibiotics

The resistome of P. aeruginosa for three β-lactam antibiotics, namely, ceftazidime, imipenem, and meropenem, was deciphered by screening a comprehensive PA14 mutant library for mutants with increased or reduced susceptibility to these antimicrobials. Confirmation of the phenotypes of all selected mutants was performed by Etest. Of the total of 78 confirmed mutants, 41 demonstrated a reduced susceptibility phenotype and 37 a supersusceptibility (i.e., altered intrinsic resistance) phenotype, with 6 mutants demonstrating a mixed phenotype, depending on the antibiotic. Only three mutants demonstrated reduced (PA0908) or increased (glnK and ftsK) susceptibility to all three antibiotics. Overall, the mutant profiles of susceptibility suggested distinct mechanisms of action and resistance for the three antibiotics despite their similar structures. More detailed analysis indicated important roles for novel and known β-lactamase regulatory genes, for genes with likely involvement in barrier function, and for a range of regulators of alginate biosynthesis.

Optimal airway antimicrobial therapy for cystic fibrosis: the role of inhaled aztreonam lysine

IMPORTANCE OF THE FIELD

Chronic endobronchial infection in cystic fibrosis (CF) leads to progressive lung function loss and respiratory failure. Most adult CF patients are infected with Pseudomonas aeruginosa, an important predictor of mortality. Suppressing chronic P. aeruginosa infection with inhaled antibiotics is standard of care for CF patients.

AREAS COVERED IN THIS REVIEW

This review describes the development (2003 - 2010) of aztreonam lysine 75 mg powder and solvent for nebulizer solution (AZLI; Cayston), an aerosolized formulation of the monobactam antibiotic aztreonam.

WHAT THE READER WILL GAIN

AZLI was studied in patients with CF and chronic P. aeruginosa airway infection. In placebo-controlled trials, AZLI improved respiratory symptoms, increased forced expiratory volume in 1 sec (FEV(1)), decreased sputum P. aeruginosa density, and was well tolerated. An open-label follow-on trial of nine 'on/off' courses showed that AZLI was safe and the effect durable with repeated administration. AZLI was recently approved for use in CF patients in Australia and the USA, and conditionally approved in Canada and the European Union. AZLI is given three times daily for 28 days (2 - 3 min/dose), followed by 28 days off-drug. AZLI is used only with the Altera Nebulizer System, which provides appropriate particle size and small airway deposition, and has excellent portability.

TAKE HOME MESSAGE

AZLI is a new therapy that is safe and effectively improves respiratory symptoms and FEV(1) in patients with CF.

Current treatment of pseudomonal infections in the elderly

Pseudomonas aeruginosa infections have emerged as a major infectious disease threat in recent decades as a result of the significant mortality of pseudomonal pneumonia and bacteraemia, and the evolving resistance exhibited by the pathogen to numerous antibacterials. Pseudomonas possesses a large genome; thus, the pathogen is environmentally adaptable, metabolically flexible, able to overcome antibacterial pressure by selecting for resistant strains and even able to accumulate resistance mechanisms, leading to multidrug resistance (MDR), an increasingly recognized therapeutic challenge. In fact, most research currently does not focus on maximizing the efficacy of available antibacterials; rather, it focuses on maximizing their ecological safety. The elderly population may be particularly prone to pseudomonal infection as a result of increased co-morbidities (such as diabetes mellitus and structural lung disease), the presence of invasive devices such as urinary catheters and feeding tubes, polypharmacy that includes antibacterials, and immune compromise related to age. However, age per se, as well as residence in nursing homes, may not predispose individuals to an increased risk for pseudomonal infection. On the other hand, age has been repeatedly outlined as a risk factor for MDR pseudomonal infections. The severity of pseudomonal infections necessitates prompt administration of appropriate antibacterials upon suspicion. Progress has been made in recognizing risk factors for P. aeruginosa infections both in hospitalized and community-residing patients. Antimicrobial therapy may be instituted as a combination or monotherapy: the debate cannot be definitively resolved since the available data are extracted from studies with varying targeted populations and varying definitions of response, adequacy and MDR. Empirical combination therapy maximizes the chances of bacterial coverage and exerts a lower resistance selection pressure. Although associated with increased percentages of adverse events, mainly as a result of the included aminoglycosides, empirical combination therapy seems a reasonable choice. Upon confirmation of Pseudomonas as the causative agent and awareness of its susceptibility profile, monotherapy is advocated by many, but not all, experts. Infections involving MDR strains can be treated with colistin, which has adequate efficacy and few renal adverse events, or doripenem. In the elderly, in addition to making dose modifications that are needed because of loss of renal function, the prescriber should be more cautious about the use of aminoglycoside-containing regimens, possibly replacing them with a combination of quinolone and a beta-lactam, notwithstanding the possible increased pressure for selection of resistance with the latter combination.

Allergic Cross-Sensitivity Between Penicillin, Carbapenem, and Monobactam Antibiotics: What are the Chances?

Objective:

To evaluate the literature on the allergic cross-reactivity between penicillin, carbapenem, and monobactam antibiotics.

Data Sources:

A MEDLINE search (1950–June 2008) of the English literature was performed using the search terms β-lactam, penicillin, monobactam, carbapenem, allergy, and cross-reactivity. References of review articles were also screened for inclusion.

Study Selection and Data Extraction:

All articles in English from the data source were identified. Studies whose primary goal was to evaluate drug hypersensitivity and the potential for cross-reactivity were evaluated.

Data Synthesis:

Many patients have reported penicillin allergies that have not been verified by skin testing; many healthcare providers avoid the use of other β-lactam antibiotics, namely carbapenems, in these patients due to fear of the potential for immunoglobulin E-mediated allergic cross-reactivity. A wide range of cross-reactivity between penicillins and carbapenems has been reported in various studies; however, more recent prospective studies have shown the incidence of cross-reactivity between penicillin and carbapenem skin tests to be around 1%. Additionally, many prescribers freely use the monobactam aztreonam in penicillin-allergic patients, believing there is no cross-reactivity between the 2 drugs. Although data support the lack of cross-reactivity between aztreonam and penicillins, immunology and some clinical data support an interaction between ceftazidime and aztreonam due to the similarity of their side chains.

Conclusions:

Although variability in cross-reactivity rates between β-lactam classes exists in the literature, the practice of avoiding carbapenems in penicillin-allergic patients should be reconsidered. With regard to monobactams, the administration of aztreonam in a patient with a ceftazidime allergy may carry an increased risk of type 1 hypersensitivity reactions and should be considered with caution. Additionally, the importance of obtaining a thorough patient history regarding the previous allergic event, proper documentation, and penicillin skin testing is re emphasized.