Antimicrobial therapy for pulmonary pathogenic colonisation and infection by Pseudomonas aeruginosa in cystic fibrosis patients

Population structure and antimicrobial susceptibility of both nonpersistent and persistent Pseudomonas aeruginosa isolates recovered from cystic fibrosis patients

Seventy-six Pseudomonas aeruginosa isolates recovered from chronically (n=18) and nonchronically (n=18) colonized cystic fibrosis (CF) patients (2002 to 2009) were grouped in separate polyclonal populations. International CF epidemic clones were not identified, but the high-risk clone ST274, also found circulating in Spanish hospitals, was present. Persistent isolates were more resistant to antibiotics than nonpersistent isolates.

Mutational activation of the AmgRS two-component system in aminoglycoside-resistant Pseudomonas aeruginosa

The amgRS operon encodes a presumed membrane stress-responsive two-component system linked to intrinsic aminoglycoside resistance in Pseudomonas aeruginosa. Genome sequencing of a lab isolate showing modest pan-aminoglycoside resistance, strain K2979, revealed a number of mutations, including a substitution in amgS that produced an R182C change in the AmgS sensor kinase product of this gene. Introduction of this mutation into an otherwise wild-type strain recapitulated the resistance phenotype, while correcting the mutation in the resistant mutant abrogated the resistant phenotype, confirming that the amgS mutation is responsible for the aminoglycoside resistance of strain K2979. The amgSR182 mutation promoted an AmgR-dependent, 2- to 3-fold increase in expression of the AmgRS target genes htpX and PA5528, mirroring the impact of aminoglycoside exposure of wild-type cells on htpX and PA5528 expression. This suggests that amgSR182 is a gain-of-function mutation that activates AmgS and the AmgRS two-component system in promoting modest resistance to aminoglycosides. Screening of several pan-aminoglycoside-resistant clinical isolates of P. aeruginosa revealed three that showed elevated htpX and PA5528 expression and harbored single amino acid-altering mutations in amgS (V121G or D106N) and no mutations in amgR. Introduction of the amgSV121G mutation into wild-type P. aeruginosa generated a resistance phenotype reminiscent of the amgSR182 mutant and produced a 2- to 3-fold increase in htpX and PA5528 expression, confirming that it, too, is a gain-of-function aminoglycoside resistance-promoting mutation. These results highlight the contribution of amgS mutations and activation of the AmgRS two-component system to acquired aminoglycoside resistance in lab and clinical isolates of P. aeruginosa.

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.

In vitro prevention of Pseudomonas aeruginosa early biofilm formation with antibiotics used in cystic fibrosis patients

The ability of antibiotics used in bronchopulmonary infections in cystic fibrosis (CF) patients to prevent Pseudomonas aeruginosa early biofilm formation was studied using a biofilm microtitre assay with 57 non-mucoid P. aeruginosa isolates (44 first colonisers and 13 recovered during the initial intermittent colonisation stage) obtained from 35 CF patients. Minimum biofilm inhibitory concentrations (BICs) of levofloxacin, ciprofloxacin, imipenem, ceftazidime, tobramycin, colistin and azithromycin were determined by placing a peg lid with a formed biofilm onto microplates containing antibiotics. A modification of this protocol consisting of antibiotic challenge during biofilm formation was implemented in order to determine the biofilm prevention concentration (BPC), i.e. the minimum concentration able to prevent biofilm formation. The lowest BPCs were for fluoroquinolones, tobramycin and colistin and the highest for ceftazidime and imipenem. The former antibiotics had BPCs identical to or only slightly higher than their minimum inhibitory concentrations (MICs) determined by standard Clinical and Laboratory Standards Institute (CLSI) microdilution and were also active on formed biofilms as reflected by their low BIC values. In contrast, ceftazidime and imipenem were less effective for prevention of biofilm formation and on formed biofilms. In conclusion, the new BPC parameter determined in non-mucoid P. aeruginosa isolates recovered during early colonisation stages in CF patients supports early aggressive antimicrobial treatment guidelines in first P. aeruginosa-colonised CF patients.

Tobramycin for the treatment of bacterial pneumonia in children

INTRODUCTION

Common etiological agents for community-acquired lower respiratory tract infection (LRTI) include Streptococcus pneumoniae, Hemophilus influenzae and Mycoplasma pneumoniae and can be easily managed with oral or intravenous antibiotics. However, LRTI in patients with underlying illnesses, such as cystic fibrosis (CF) and immune deficiency, or on ventilator support is difficult to manage because these are caused by Gram-negative bacilli. Tobramycin has been shown to be effective in the management of these patients.

AREAS COVERED

Information about the antimicrobial activity, pharmacological aspects (including pharmacokinetics and pharmacodynamics), clinical efficacy, safety and side effects of tobramycin have been covered in this review.

EXPERT OPINION

A major advance for the use of tobramycin has occurred with its use by the inhalational route, in children with CF. The inhalation route provides the advantage of ease of administration for prolonged periods at home and allows use of very high doses. Systematic reviews suggest that tobramycin inhalation improves outcome, decreases the need for hospitalization and decreases the need for use of frequent systemic antibiotics in CF patients colonized with pseudomonas. Data on the efficacy of inhaled tobramycin in non-CF bronchiectasis are scarce, as are data on the prevention and treatment of ventilator-associated pneumonia, and on the role of combining inhaled tobramycin with systemic tobramycin. Despite limitations, this drug has the potential to be used in various conditions other than CF.

[Chronic bronchial infection: the problem of Pseudomonas aeruginosa]

Pathogenic bronchopulmonary colonizations and the exacerbations produced are among the most important causes of reduced pulmonary function in patients with bronchiectasis. The most frequent pathogens in these patients are Haemophilus influenzae and Pseudomonas aeruginosa. Lesions are produced by the local inflammatory process and the vicious circle developed by antigen stimulation, the release of inflammatory mediators, the presence of neutrophils, the increase of bacterial inoculum and the release of bacterial exoproducts. P. aeruginosa has been demonstrated to affect the patients with bronchiectasis and poorest quality of life and to colonize those with the poorest pulmonary function and the highest number of antimicrobial treatments. In bronchiectasis, as in chronic obstructive pulmonary disease (COPD) or cystic fibrosis, P. aeruginosa is able to colonize the respiratory mucosa chronically. Due to the ecological niche occupied by P. aeruginosa and the multitude of cycles with antimicrobial agents to which these patients are subjected, the development of antimicrobial resistance is highly likely, encouraged by the high proportion of hypermutation variants in existence. Likewise, P. aeruginosa naturally grows in the form of biofilms on the mucosal surface, greatly contributing to its persistence. Antimicrobial treatment in patients with bronchiectasis and P. aeruginosa colonization should be based on antimicrobial agents, alone or in combination, that do not lose activity when acting on biofilms.

[Treatment of non-cystic fibrosis bronchiectasis]

Bronchiectasis is currently growing in importance due to both the increase in the number of diagnoses made as well as the negative impact that its presence has on the baseline disease that generates it. A fundamental aspect in these patients is the colonization and infection of the bronchial mucous by potentially pathogenic microorganisms (PPM), which are the cause in most cases of the start of the chronic inflammatory process that results in the destruction and dilatation of the bronchial tree that is characteristic in these patients. The treatment of the colonization and chronic bronchial infection in these patients should be based on prolonged antibiotic therapy in its different presentations. Lately, the inhaled form is becoming especially prominent due to its high efficacy and limited production of important adverse effects. However, one must not overlook the fact that the management of patients with bronchiectasis should be multidisciplinary and multidimensional. In addition to antibiotic treatment, the collaboration of different medical and surgical specialties is essential for the management of the exacerbations, nutritional aspects, respiratory physiotherapy, muscle rehabilitation, complications, inflammation and bronchial hyperreactivity and the hypersecretion that characterizes these patients.

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?

The effect of early Pseudomonas aeruginosa treatment on lung function in pediatric cystic fibrosis

OBJECTIVE

Our aim was to assess the effect of treatment of early infection of P. aeruginosa on pulmonary function in pediatric CF patients.

METHODS

This was a retrospective cohort study of P. aeruginosa negative CF patients followed at Sick Kids from 1990 to 2007. Early P. aeruginosa infection was defined as the first respiratory culture for P. aeruginosa; patients were included if 5 years of follow-up pulmonary function data were available. Patients were divided into three groups (group 1: never infected, group 2: infected with subsequent clearance, and group 3: chronic infection or still receiving antipseudomonal antibiotics). Hierarchical linear models were used to estimate the effect of P. aeruginosa infection on spirometry. FEV(1) % predicted was the primary outcome.

RESULTS

116 patients were included. Forty-six (40%) patients remained P. aeruginosa negative throughout the observation period, 29 (25%) patients transiently infected with P. aeruginosa, and 41 (35%) patients were either currently infected or still receiving treatment. Baseline lung function was the same for all groups. Annual decline in FEV(1) % predicted during the study period was not different (-0.6%/year for patients that were never infected and -1.3%/year among patients previously infected).

CONCLUSIONS

Lung function was not different between patients with early P. aeruginosa infection and those that never had P. aeruginosa infection. However given the slow rate of FEV(1) decline in the study population, a longer observation period and/or more sensitive outcomes measures may be required to exclude long-term detrimental effects of transient P. aeruginosa infection on lung function in CF patients.

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?

Management of refractory Pseudomonas aeruginosa infection in cystic fibrosis

Cystic fibrosis (CF) is the most common life-limiting inherited disease in Caucasian populations. The main cause of death in CF patients is respiratory failure resulting from chronic pulmonary infection. Pseudomonas aeruginosa is the most prevalent organism in the airway colonization of CF patients, and its persistence in the airways has been related to greater morbidity with a more rapid deterioration in lung function. P. aeruginosa has enormous genetic and metabolic flexibility that allows it to adapt and persist within the airways of CF patients, and it has the ability to easily acquire antimicrobial resistance. For these reasons, the management of infections and chronic colonization by P. aeruginosa remains a challenge for physicians. This article reviews the current and future antibacterial chemotherapy options for respiratory pseudomonal infection in CF patients.

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.

Prevalence of virulence genes among bulgarian nosocomial and cystic fibrosis isolates of pseudomonas aeruginosa

The aim of this study was to evaluate the prevalence of some virulence genes among 202 Pseudomonas aeruginosa isolates from cystic fibrosis (CF) patients (n=42) and non-CF in-patients (n=160) and to analyze the values according to the patient groups, infection localization and antimicrobial resistance. The following frequencies in all studied strains were established: algD (encoding GDP-mannose 6-dehydrogenase AlgD) – 91.1%, pilB (type IV fimbrial biogenesis protein PilB) – 23.8%, nan1 (neuraminidase) – 21.3%, lasB (elastase LasB) – 100%, plcH (haemolytic phospholipase C precursor) – 91.6%, exoS (exoenzyme S) – 62.4%, and exoU (exoenzyme U) – 30.2%. The prevalence of nan1 was significantly higher (P<0.01) in CF isolates (38.1%) than that in non-CF isolates (16.9%). The nan1–positive CF strains were cultured from 16 patients with recurrent lung exacerbations. This study revealed a statistically significant difference (P<0.01) between the portion of multidrug-resistant (MDR) nosocomial P.aeruginosa strains containing a large number (≥5) of virulence genes (38.1%) and the respective part of non-MDR isolates (17.6%). Moreover, pilB, exoU and nan1 manifested a higher spread (P<0.001) among MDR than in non-MDR strains (respectively, 39.1% vs. 13.2%; 40.2% vs. 17.7% and 26.1% vs. 4.4%). In conclusion, the dissemination of nan1 in CF isolates was moderate and correlated with the lower proportion of patients with lung exacerbations. The molecular-genetic detection of this gene may be used as an indirect measure of CF pulmonary disease evolution. Simultaneous determination of virulence factors and antimicrobial resistance is the contemporary approach for examination of the microbiological aspects of infections caused by P. aeruginosa.

Combination of 16S rRNA variable regions provides a detailed analysis of bacterial community dynamics in the lungs of cystic fibrosis patients

Chronic bronchopulmonary bacterial infections remain the most common cause of morbidity and mortality among patients with cystic fibrosis (CF). Recent community sequencing work has now shown that the bacterial community in the CF lung is polymicrobial. Identifying bacteria in the CF lung through sequencing can be costly and is not practical for many laboratories. Molecular techniques such as terminal restriction fragment length polymorphism or amplicon length heterogeneity-polymerase chain reaction (LH-PCR) can provide many laboratories with the ability to study CF bacterial communities without costly sequencing. The aim of this study was to determine if the use of LH-PCR with multiple hypervariable regions of the 16S rRNA gene could be used to identify organisms found in sputum DNA. This work also determined if LH-PCR could be used to observe the dynamics of lung infections over a period of time. Nineteen samples were analysed with the V1 and the V1_V2 region of the 16S rRNA gene. Based on the amplicon size present in the V1_V2 region, Pseudomonas aeruginosa was confirmed to be in all 19 samples obtained from the patients. The V1 region provided a higher power of discrimination between bacterial profiles of patients. Both regions were able to identify trends in the bacterial population over a period of time. LH profiles showed that the CF lung community is dynamic and that changes in the community may in part be driven by the patient's antibiotic treatment. LH-PCR is a tool that is well suited for studying bacterial communities and their dynamics.

Anti-biofilm and resistance suppression activities of CXA-101 against chronic respiratory infection phenotypes of Pseudomonas aeruginosa strain PAO1

OBJECTIVES

Biofilm growth, mucoid phenotype and proficient resistance development by hypermutable strains dramatically limit the efficacy of current therapies for Pseudomonas aeruginosa chronic respiratory infection (CRI) in cystic fibrosis (CF) patients. We evaluated the activity of the new cephalosporin CXA-101, ceftazidime, meropenem and ciprofloxacin against biofilms of wild-type PAO1 and its mucoid (mucA), hypermutable (mutS) and mucoid-hypermutable derivatives, and analysed the capacity of these strains to develop resistance during planktonic and biofilm growth.

METHODS

MICs and MBCs were determined by microdilution, and mutant frequencies were determined at 4x and 16x the MICs. Biofilms were formed using a modified Calgary device and were incubated for 24 h with 0x, 1x, 4x or 16x the MIC of each antibiotic. Biofilms were plated, and total cells and resistant mutants enumerated.

RESULTS

CXA-101 showed concentration-independent biofilm bactericidal activity, being the most potent agent tested at 1x the MIC for wild-type, mucoid and hypermutable strains. The spontaneous mutant frequencies for CXA-101 were extremely low (<5 x 10(-11)), even for the hypermutable strain at low concentrations (4x the MIC), in sharp contrast to the other antipseudomonal agents. Accordingly, mutants resistant to 4x the MIC of CXA-101 did not emerge in biofilms for any of the strains/concentrations tested.

CONCLUSION

These data strongly suggest that resistance to CXA-101 (at least 4x the MIC) cannot be driven by single-step mutations, either in planktonic or in biofilm growth. CXA-101 shows encouraging properties for the treatment of CRI by P. aeruginosa, which need to be further evaluated in animal models and pertinent clinical trials.

Population pharmacokinetic comparison and pharmacodynamic breakpoints of ceftazidime in cystic fibrosis patients and healthy volunteers

Despite the promising activity of ceftazidime against Pseudomonas aeruginosa and Burkholderia cepacia, there has not yet been a study that directly compared the pharmacokinetics (PK) of ceftazidime in cystic fibrosis (CF) patients and healthy volunteers by population PK methodology. We assessed the population PK and PK/pharmacodynamic (PD) breakpoints of ceftazidime in CF patients and healthy volunteers. Eight CF patients (total body weight [WT] [average +/- standard deviation] = 42.9 +/- 18.4 kg) and seven healthy volunteers (WT = 66.2 +/- 4.9 kg) received 2 g ceftazidime as a 5-min intravenous infusion. High-performance liquid chromatography (HPLC) was used for drug analysis, and NONMEM (results reported), S-ADAPT, and NPAG were used for parametric and nonparametric population PK modeling. We considered linear and allometric body size models to scale clearance and volume of distribution. Monte Carlo simulations were based on a target time of non-protein-bound plasma concentration of ceftazidime above MIC of > or =65%, which represents near-maximal killing. Unscaled total clearance was 19% lower in CF patients, and volume of distribution was 36% lower. Total clearance was 7.82 liters/h for CF patients and 6.68 liters/h for healthy volunteers with 53 kg fat-free mass. Allometric scaling by fat-free mass reduced the between-subject variability by 32% for clearance and by 18 to 26% for volume of both peripheral compartments compared to linear scaling by WT. A 30-min ceftazidime infusion of 2 g/70 kg WT every 8 h (q8h) achieved robust (> or =90%) probabilities of target attainment (PTAs) for MICs of < or =1 mg/liter in CF patients and < or =3 mg/liter in healthy volunteers. Alternative modes of administration achieved robust PTAs up to markedly higher MICs of < or =8 to 12 mg/liter in CF patients for 5-h infusions of 2 g/70 kg WT q8h and < or =12 mg/liter for continuous infusion of 6 g/70 kg WT daily.

Inhaled colistin as adjunctive therapy to intravenous colistin for the treatment of microbiologically documented ventilator-associated pneumonia: a comparative cohort study

Ventilator-associated pneumonia (VAP) as a result of multidrug-resistant Gram-negative bacteria has contributed to the revival of the use of intravenous (i.v.) colistin. However, the additional administration of inhaled colistin for VAP is controversial. We performed a retrospective cohort study of patients with microbiologically documented VAP who received i.v. colistin with or without inhaled colistin. Seventy-eight patients with VAP received i.v. plus inhaled colistin, whereas 43 patients received i.v. colistin alone. The mean +/- SD daily dosage of i.v. colistin was 7.0 +/- 2.4 and 6.4 +/- 2.3 million international units (IU), respectively (p 0.13); the average daily dosage of inhaled colistin was 2.1 +/- 0.9 million IU. The outcome of infection was cure for 62/78 (79.5%) patients who received i.v. plus inhaled colistin vs. 26/43 (60.5%) patients who received i.v. colistin alone (p 0.025); all-cause in-hospital mortality was 31/78 (39.7%) vs. 19/43 (44.2%), respectively (p 0.63); all-cause intensive care unit (ICU) mortality was 28/78 (35.9%) vs. 17/43 (39.5%), respectively (p 0.92). The use of inhaled colistin was independently associated with the cure of VAP in a multivariable analysis (OR 2.53, 95% CI 1.11-5.76). Independent predictors of mortality were a higher APACHE II score (OR 1.12, 95% CI 1.04-1.20), presence of malignancy (OR 4.11, 95% CI 1.18-14.23) and lower daily dosage of i.v. colistin (OR 0.81, 95% CI 0.68-0.96). The outcome of VAP was better in patients who received inhaled colistin with i.v. colistin than those who received i.v. colistin alone. There was no difference in all-cause in-hospital and ICU mortality between the two groups. Randomized controlled trials are needed to evaluate further the role of inhaled colistin in VAP.

Inhaled therapeutics for prevention and treatment of pneumonia

The lungs are the most common site of serious infection owing to their large surface area exposed to the external environment and minimum barrier defense. However, this architecture makes the lungs readily available for topical therapy. Therapeutic aerosols include those directed towards improving mucociliary clearance of pathogens, stimulation of innate resistance to microbial infection, cytokine stimulation of immune function and delivery of antibiotics. In our opinion inhaled antimicrobials are underused, especially in patients with difficult-to-treat lung infections. The use of inhaled antimicrobial therapy has become an important part of the treatment of airway infection with Pseudomonas aeruginosa in cystic fibrosis and the prevention of invasive fungal infection in patients undergoing heart and lung transplantation. Cytokine inhaled therapy has also been explored in the treatment of neoplastic and infectious disease. The choice of pulmonary drug delivery systems remains critical as air-jet and ultrasonic nebulizer may deliver sub-optimum drug concentration if not used properly. In future development of this field, we recommend an emphasis on the study of the use of aerosolized hypertonic saline solution to reduce pathogen burden in the airways of subjects infected with microbes of low virulence, stimulation of innate resistance to prevent pneumonia in immunocompromised subjects using cytokines or synthetic pathogen-associated molecular pattern analogues and more opportunities for the use of inhaled antimicrobials. These therapeutics are still in their infancy but show great promise.

[Microbiological diagnosis of bronchopulmonary colonization-infection in cystic fibrosis]

Cystic fibrosis (CF), a condition produced by mutations in the gene that encodes the cystic fibrosis transmembrane conductance regulator, is the most prevalent autosomal-recessive hereditary disease in caucasian populations. Among other repercussions, this defect leads to an alteration of respiratory secretions and determines a predisposition for chronic bronchopulmonary colonization-infection, which is the main driver of the high morbidity and early mortality of CF patients. Colonization by Staphylococcus aureus and Haemophilus influenzae is frequent in children younger than 10 years, but mucoid Pseudomonas aeruginosa is by far the most relevant pathogen in adults with CF and is responsible for the progressive bronchopulmonary deterioration. As a consequence of repeated, long-lasting antimicrobial treatments and deterioration of lung function, colonization by multidrug-resistant Gram-negative bacilli, such as Stenotrophomonas maltophilia, Achromobacter spp. and Burkholderia cepacia complex, is also frequent in adult CF patients. The special characteristics of the pathologic process and the microorganisms implicated in CF make it advisable to consider microbiological follow-up of chronic bronchopulmonary colonization-infection in these patients a specific diagnostic entity.

Chronic Pseudomonas aeruginosa infection in chronic obstructive pulmonary disease

BACKGROUND

Pseudomonas aeruginosa infections are increasingly associated with acute exacerbations in chronic obstructive pulmonary disease (COPD). We aimed to determine whether an underlying chronic infection might be behind this process and to determine the epidemiological characteristics of the isolates involved, to implement useful protocols for preventing and treating these infections.

METHODS

P. aeruginosa isolates obtained from respiratory samples of 13 patients with COPD and from blood samples of 10 patients in intensive care units were investigated. In 8 patients with COPD, isolates were obtained during sequential exacerbation episodes. Five patients presented a single infection episode. Production of virulence determinants and genetic relationships were analyzed in all isolates.

RESULTS

Patients with COPD were usually infected with 1 P. aeruginosa clone that remained in the lung for years, without evidence of interpatient transmission. During chronic infection, each clone diversified, which led to the coexistence of isolates with different morphotypes and antibiotic susceptibility. Overall, P. aeruginosa evolved toward an increased mutation rate, increased antibiotic resistance, and reduced production of proteases. Isolates from samples of infected lungs tend to be less cytotoxic and motile and to produce more biofilm, compared with isolates from blood samples.

CONCLUSION

These results provide the first evidence supporting the hypothesis that P. aeruginosa causes chronic infections in COPD, with patterns of infection and evolution that resemble those observed in cystic fibrosis. Experience gained from treating cystic fibrosis might be useful for implementing new procedures for the prevention, diagnosis, and treatment of infection due to P. aeruginosa in COPD.

Shifting patterns of inhaled antibiotic use in cystic fibrosis

RATIONALE

Antibiotic inhalation has become widely accepted as a standard treatment for cystic fibrosis (CF) airway infection. We assessed the prevalence and context of inhaled antibiotic use in the North American CF population. Our working hypothesis was that a shift from acute to chronic use of inhaled antibiotics has coincided with increased prevalence of use among CF patients.

METHODS

Descriptive statistics were collected for 30,833 patients enrolled in the Epidemiologic Study of CF (ESCF) during 1996 through 2005. A multivariate analysis was performed on data from a subgroup of 18,021 patients enrolled in ESCF during 2003 through 2005.

RESULTS

The prevalence of inhaled antibiotic use in the North American CF population increased during 1996 through 2005 due to increased chronic use, while acute use to treat pulmonary exacerbations decreased. In 2005, 50% of CF patients used inhaled tobramycin and 9% used inhaled colistin chronically; most of the latter used both agents concurrently. Airway obstruction severity and airway infection status were predictors of inhaled antibiotic use.

CONCLUSIONS

Increased chronic use and decreased acute use of inhaled antibiotics presumably reflect a shift toward more proactive management of airway infections in the North American CF population. The effects of these usage patterns on long-term clinical outcomes and emergence of antibiotic-resistant Pseudomonas aeruginosa strains warrant further study.

Inhaled aminoglycosides in cancer patients with ventilator-associated Gram-negative bacterial pneumonia: safety and feasibility in the era of escalating drug resistance

We sought to evaluate the safety and feasibility of inhaled aminoglycosides or colistin in cancer patients with ventilator-associated pneumonia (VAP) due to Gram-negative bacteria (GNB). A retrospective case-matched study was obtained after obtaining IRB approval in patients at the intensive care unit at our NCI-designated comprehensive cancer center between 1999 and 2005. Sixteen patients with GNB-VAP who received inhaled aminoglycosides or colistin were compared with 16 patients who had received these antibiotics intravenously alone. Eligible patients were required to have received at least six doses of inhaled therapy, or 3 or more days of intravenous therapy. Clinical Pulmonary Infection Scores were used to assess pneumonia severity. Standard ATS criteria were used to define VAP. Patients treated with inhaled antibiotics were less likely to have received corticosteroids (13% vs 50%; P < 0.02) and had a higher median baseline creatinine level (0.85 vs 0.6 mg/dL; P < 0.02) than patients treated intravenously. Pseudomonas aeruginosa (69%) was the most common cause of VAP. There were no serious adverse events associated with inhaled antibiotics. Patients who received these antibiotics intravenously developed renal dysfunction (31%); none of the patients treated with inhaled antibiotics developed nephrotoxicity (P < or = 0.04). Patients treated with inhaled antibiotics were more likely to have complete resolution of clinical (81% vs 31% in the intravenous antibiotic group; P < 0.01) and microbiologic infection (77% vs 8% in the intravenous antibiotic group: P < 0.0006). In a multivariate analysis adjusted for corticosteroid use, inhaled antibiotic therapy was predictive of complete clinical resolution (odds ratio [OR], 6.3; 95% confidence interval [CI], 1.1, 37.6; P < 0.04) and eradication of causative organisms (OR 36.7; 95% CI, 3.3, 412.2; P < 0.003). In critically ill cancer patients with Gram-negative VAP, inhaled aminoglycosides were tolerated without serious toxicity and may lead to improved outcome.

Stability of colistin methanesulfonate in pharmaceutical products and solutions for administration to patients

Colistin methanesulfonate (CMS) has the potential to hydrolyze in aqueous solution to liberate colistin, its microbiologically active and more toxic parent compound. While conversion of CMS to colistin in vivo is important for bactericidal activity, liberation of colistin during storage and/or use of pharmaceutical formulations may potentiate the toxicity of CMS. To date, there has been no information available regarding the stability of CMS in pharmaceutical preparations. Two commercial CMS formulations were investigated for stability with respect to colistin content, which was measured by a specific high-performance liquid chromatography method. Coly-Mycin M Parenteral (colistimethate lyophilized powder) was stable (<0.1% of CMS present as colistin) for at least 20 weeks at 4 degrees C and 25 degrees C at 60% relative humidity. When Coly-Mycin M was reconstituted with 2 ml of water to a CMS concentration of 200 mg/ml for injection, Coly-Mycin M was stable (<0.1% colistin formed) for at least 7 days at both 4 degrees C and 25 degrees C. When further diluted to 4 mg/ml in a glucose (5%) or saline (0.9%) infusion solution as directed, CMS hydrolyzed faster at 25 degrees C (<4% colistin formed after 48 h) than at 4 degrees C (0.3% colistin formed). The second formulation, CMS Solution for Inhalation (77.5 mg/ml), was stable at 4 degrees C and 25 degrees C for at least 12 months, as determined based on colistin content (<0.1%). This study demonstrated the concentration- and temperature-dependent hydrolysis of CMS. The information provided by this study has important implications for the formulation and clinical use of CMS products.

A German external quality survey of diagnostic microbiology of respiratory tract infections in patients with cystic fibrosis

BACKGROUND

The goal of this pilot study was to design an external quality assessment (EQA) scheme for German cystic fibrosis (CF) clinical microbiology laboratories. Therefore, a multicentre study of 18 German CF laboratories was performed to evaluate their proficiency in analyzing CF respiratory secretions.

METHODS

Simulated clinical specimens containing a set of four frequent CF pathogens, namely two Pseudomonas aeruginosa strains differing in morphotype (mucoid versus non-mucoid) and resistotype, one Staphylococcus aureus strain and one Burkholderia multivorans strain, were distributed to each laboratory. Isolation, identification and antimicrobial susceptibility testing (AST) of any bacterial pathogen present and completion of a questionnaire about applied microbiological protocols were requested.

RESULTS

Three of four strains were isolated and identified correctly by almost all laboratories. B. multivorans was once misidentified as Burkholderia cenocepacia. Fourteen laboratories failed to detect the second multidrug resistant P. aeruginosa isolate. AST errors occurred most often for P. aeruginosa 2 followed by B. multivorans, P. aeruginosa 1 and S. aureus. Evaluation of the questionnaires revealed major differences in cultivation and identification techniques applied by the participating laboratories.

CONCLUSIONS

A periodical EQA programme for German CF laboratories and standardized microbiological procedures seem to be necessary to advance diagnostic microbiology employed on CF respiratory tract specimens and may help to improve anti-infective treatment and infection control practices for CF patients.

[Administration of anti-infective agents through the inhaled route]

OBJECTIVE

To report the doses of inhaled anti-infective agents described in the literature for both the adult and paediatric population. In the case of anti-infective agents which were not approved for inhaled administration, to propose the optimum manner in which these should be prepared in order to achieve osmolality and pH values as similar as possible to physiological values.

METHOD

A search was carried out of Pubmed (between 1960 and 2005) for each of the anti-infective agents using the words "inhalation OR inhaled OR aerosol OR aerosolized OR nebulized". We also consulted text books, Micromedex and the technical specifications of the pharmaceutical products. Nebulised solutions were prepared using the drugs for which information was found. The drugs approved for inhaled administration were prepared according to the manufacturers recommendations. For anti-infective agents which were not approved for inhaled administration, the raw materials and the branded drug products for intravenous administration available at our hospital were diluted using physiological saline solution and/or water for injection up to a final volume of 4-5 ml. The osmolality and pH values of all the solutions were measured. The optimum form of preparation was considered to be one with values as close as possible to between 150 and 550 mOsm/kg for osmolatity osmolality and 7 +/- 0.5 for pH.

RESULTS

Information about doses of 18 inhaled anti-infective agents was found (12 antibiotics, 5 antifungals and 1 antiviral); paediatric doses were described in 9 of these. Three of the anti-infective agents reviewed were approved for inhaled use in adult patients and four in paediatric patients. Of the 48 recommendations for dilution suggested for administration, two had an osmolality > 1,100 mOsm/kg and 5 an osmolality of < 100 mOsm/kg. Two dilutions had a pH > 8 and 14 a pH < 5.

CONCLUSIONS

There is limited literature regarding the doses of anti-infective agents for inhaled administration. The majority of anti-infective agents are not approved for inhaled administration. The dilution of the raw material or proprietary drugs with water or physiological saline solution for intravenous administration achieved solutions with appropriate osmolality in the majority of cases. Some of the solutions have extreme osmolality and/or pH levels, implying that it is reasonable to expect a greater risk of bronchospasm.

Systematic comparison of the population pharmacokinetics and pharmacodynamics of piperacillin in cystic fibrosis patients and healthy volunteers

Respiratory tract infections cause 90% of premature mortality in patients with cystic fibrosis (CF). Treatment of Pseudomonas aeruginosa infection is often very problematic. Piperacillin-tazobactam has good activity against P. aeruginosa, but its pharmacokinetics (PK) in CF patients has not been compared to the PK in healthy volunteers in a controlled clinical study. Therefore, we compared the population PK and pharmacodynamics (PD) of piperacillin between CF patients and healthy volunteers. We studied 8 adult (median age, 20 years) CF patients (average total body weight [WT], 43.1 +/- 7.8 kg) and 26 healthy volunteers (WT, 71.1 +/- 11.8 kg) who each received 4 g piperacillin as a 5-min intravenous infusion. We determined piperacillin levels by high-performance liquid chromatography, and we used NONMEM for population PK and Monte Carlo simulation. We used a target time of nonprotein-bound concentration above the MIC of 50%, which represents near-maximal bacterial killing. Unscaled total clearance was 25% lower, and the volume of distribution was 31% lower in CF patients. Allometric scaling by lean body mass reduced the unexplained (random) between-subject variability in clearance by 26% compared to the variability of linear scaling by WT. A standard dosage regimen of 3 g/70 kg body WT every 4 h as a 30-min infusion (daily dose, 18 g) achieved a robust (> or =90%) probability-of-target attainment (PTA) for MICs of < or =12 mg/liter in CF patients and < or =16 mg/liter in healthy volunteers. Alternative modes of administration allowed a marked dose reduction to 9 g daily. Prolonged (4-h) infusions of 3 g/70 kg WT every 8 h and continuous infusion (daily dose, 9 g), achieved a robust PTA for MICs of < or =16 mg/liter in both groups. Piperacillin achieved PTA expectation values of 64% and 89% against P. aeruginosa infection in CF patients, based on susceptibility data from two German CF clinics.

Approaches to the Treatment of Initial Pseudomonas aeruginosa Infection in Children Who Have Cystic Fibrosis

Pseudomonas aeruginosa remains an important cause of pulmonary disease in patients who have cystic fibrosis. The development of antimicrobial therapy directed against this organism has resulted in the preservation of lung function and improved longevity. Efficacy has been demonstrated with agents administered via parenteral, inhaled, and oral routes. The optimal antibiotic regimen remains unclear. There is an active effort to use randomized, controlled clinical trials to rigorously test effective antibiotic for the eradication of P aeruginosa in young children or at least to delay the establishment of chronic infection.

Salvage treatment of pneumonia and initial treatment of tracheobronchitis caused by multidrug-resistant Gram-negative bacilli with inhaled polymyxin B

Systemic colistin has shown efficacy against multidrug-resistant Pseudomonas aeruginosa and Acinetobacter spp., but it has presented poor results in pneumonia. Aerosolized polymyxin in cystic fibrosis patients has had good results. In this study, inhaled polymyxin B was used to treat respiratory infections by multidrug-resistant Gram-negative bacilli (MR-GNBs). Nineteen patients were treated with inhaled polymyxin B: 14 pneumonia, most of which had previously failed treatment with intravenous polymyxin B, and 5 tracheobronchitis. Inhaled polymyxin B was given at the dose of 500,000 IU twice a day after an aerosolized beta(2)-agonist. In pneumonia, inhaled and intravenous polymyxin B was given together. Median age was 69 years; 89% were in the intensive care unit. Sixteen infections (84%) were caused by P. aeruginosa. Klebsiella pneumoniae, Alcaligenes xylosoxidans, and Burkholderia sp. caused one infection each. In the 14 pneumonia cases, median of previous use of intravenous polymyxin B was 20 days (range, 0-32). Inhaled polymyxin B was used for a mean of 14 days (range, 4-25). Cure occurred in 10 (53%) patients, improvement in 8 (42%), and failure in 1. Nine patients died during hospitalization (all with pneumonia). Adverse events occurred in 4 patients without interruption of inhalation. This is the largest report using inhaled polymyxin B to treat nosocomial pneumonia by MR-GNB that had failed intravenous polymyxin B. It was also effective alone in P. aeruginosa tracheobronchitis.

Coagulopathy in two patients with cystic fibrosis treated with ciprofloxacin

We report two cases of prolonged blood clotting times as demonstrated by a raised international normalised ratio and elevated activated partial thromboplastin time in patients with cystic fibrosis taking ciprofloxacin. The potential mechanisms of a coagulopathy of this picture as an adverse drug reaction with ciprofloxacin are discussed along with the possible clinical consequences for patients with cystic fibrosis.

Influence of high mutation rates on the mechanisms and dynamics of in vitro and in vivo resistance development to single or combined antipseudomonal agents

We studied the mechanisms and dynamics of the development of resistance to ceftazidime (CAZ) alone or combined with tobramycin (TOB) or ciprofloxacin (CIP) in vitro and in vivo (using a mouse model of lung infection with human antibiotic regimens). Pseudomonas aeruginosa strain PAO1 and its hypermutable derivative PAODeltamutS were used, and the results were compared with those previously obtained with CIP, TOB, and CIP plus TOB (CIP-TOB) under the same conditions. An important (200-fold) amplification of the number of resistant mutant cells was documented for PAODeltamutS-infected mice that were under CAZ treatment compared to the number for mice that received placebo, whereas the median number of resistant mutant cells was below the detection limits for mice infected by PAO1. These results were intermediate between the high amplification with CIP (50,000-fold) and the low amplification with TOB (10-fold). All CAZ-resistant single mutant cells selected in vitro or in vivo hyperproduced AmpC. On the other hand, the three combinations studied were found to be highly effective in the prevention of in vivo resistance development in mice infected with PAODeltamutS, although the highest therapeutic efficacy (in terms of mortality and total bacterial load reduction) compared to those of the individual regimens was obtained with CIP-TOB and the lowest was with CAZ-CIP. Nevertheless, mutant cells that were resistant to the three combinations tested were readily selected in vitro for PAODeltamutS (mutation rates from 1.2 x 10(-9) to 5.8 x 10(-11)) but not for PAO1, highlighting the potential risk for antimicrobial resistance development associated with the presence of hypermutable strains, even when combined therapy was used. All five independent CAZ-TOB-resistant PAODeltamutS double mutants studied presented the same resistance mechanism (AmpC hyperproduction plus an aminoglycoside resistance mechanism not related to MexXY), whereas four different combinations of resistance mechanisms were documented for the five CAZ-CIP-resistant double mutants.

[Clinical and therapeutic management of respiratory tract infections. Consensus document of the Andalusian Infectious Diseases Society and the Andalusian Family and Community Medicine Society]

Respiratory tract infections are frequent and they are one of the commonest causes of antibiotic prescription. However, there are few clinical guidelines that consider this group of infections. This document has been written by the Andalusian Infectious Diseases Society and the Andalusian Family and Community Medicine Society. The primary objective has been to define the recommendations for the diagnosis and antibiotic treatment of respiratory tract infections apart from pneumonia. The clinical syndromes evaluated have been: a) pharyngitis; b) sinusitis; c) acute otitis media and otitis externa; d) acute bronchitis, laryngitis, epiglottitis; e) acute exacerbation of chronic bronchitis; and f) respiratory infectious in patients with bronchiectasis. This document has focused on immunocompetent patients.

Pseudomonas aeruginosa: resistance and therapeutic options at the turn of the new millennium

Pseudomonas aeruginosa is a major cause of nosocomial infections. This organism shows a remarkable capacity to resist antibiotics, either intrinsically (because of constitutive expression of beta-lactamases and efflux pumps, combined with low permeability of the outer-membrane) or following acquisition of resistance genes (e.g., genes for beta-lactamases, or enzymes inactivating aminoglycosides or modifying their target), over-expression of efflux pumps, decreased expression of porins, or mutations in quinolone targets. Worryingly, these mechanisms are often present simultaneously, thereby conferring multiresistant phenotypes. Susceptibility testing is therefore crucial in clinical practice. Empirical treatment usually involves combination therapy, selected on the basis of known local epidemiology (usually a beta-lactam plus an aminoglycoside or a fluoroquinolone). However, therapy should be simplified as soon as possible, based on susceptibility data and the patient's clinical evolution. Alternative drugs (e.g., colistin) have proven useful against multiresistant strains, but innovative therapeutic options for the future remain scarce, while attempts to develop vaccines have been unsuccessful to date. Among broad-spectrum antibiotics in development, ceftobiprole, sitafloxacin and doripenem show interesting in-vitro activity, although the first two molecules have been evaluated in clinics only against Gram-positive organisms. Doripenem has received a fast track designation from the US Food and Drug Administration for the treatment of nosocomial pneumonia. Pump inhibitors are undergoing phase I trials in cystic fibrosis patients. Therefore, selecting appropriate antibiotics and optimising their use on the basis of pharmacodynamic concepts currently remains the best way of coping with pseudomonal infections.