Michelle Prickett

Evolution of Pseudomonas aeruginosa type III secretion in cystic fibrosis: a paradigm of chronic infection

Pseudomonas aeruginosa (PA) from acute and chronic (eg, cystic fibrosis (CF)) infections differ in several respects, but they can worsen prognosis in each context. Factors that facilitate conversion from an acute to chronic phenotype are poorly understood. T3 secretion proteins are virulence factors associated with poorer outcomes in acute infections, but little is known about their role in CF. We wished to characterize T3 secretion in CF PA isolates and to examine its role in clinical outcomes. A total of 114 CF subjects were divided into 3 cohorts: 1st infected individuals, CI children, and adults. Serial respiratory cultures were analyzed for T3 secretion. Serial spirometry and exacerbation data were collected prospectively. In 1st infection, 45.2% +/- 9.1% of PA isolates secreted T3 proteins compared with 29.1% +/- 4.2% and 11.5% +/- 3.0% in CI children and CI adults, respectively (P < 0.001). An inverse correlation was observed between duration of PA infection and percent T3 positive isolates (r = -0.32, P < 0.001). Overall, no association was observed between T3 secretion and pulmonary outcomes, but in the subgroup of subjects who had at least 1 T3 positive organism, T3 secretion was inversely correlated with the forced expiratory volume in 1 s (FEV(1)) decline (r = -0.35, P = 0.02). In 1st infection, 82% of cultures grew either all or no T3-positive organisms. In these patients, T3 secretion was associated with a greater risk of subsequent PA isolation (P < 0.001). In CF, PA T3 secretion decreases with residence time in lung, may predict FEV(1) decline in patients who have detectable T3 organisms, and may facilitate persistence after 1st infection.

Aminoglycoside resistance of Pseudomonas aeruginosa in cystic fibrosis results from convergent evolution in the mexZ gene

Rationale Aminoglycoside (AG) resistance of Pseudomonas aeruginosa in cystic fibrosis (CF) is associated with poorer clinical outcomes and is usually due to overexpression of the efflux pump MexXY. MexXY is regulated by mexZ, one of the most commonly mutated genes in CF P. aeruginosa isolates. Little is known about the evolutionary relationship between AG resistance, MexXY expression and mexZ mutations. Objectives To test the hypothesis that AG resistance in P. aeruginosa develops in parallel with higher MexXY expression and mexZ mutations. Methods CF P. aeruginosa isolates were compared for chronically infected (CI) adults, CI children and children with new infection. Measurements One P. aeruginosa isolate from each patient was analysed for mexZ mutations, mexY mRNA expression and amikacin resistance. Main results 56 patients with CF were enrolled: 21 children with new P. aeruginosa infection, 18 CI children and 17 CI adults. Amikacin resistance and mexY mRNA expression were higher in cohorts with longer P. aeruginosa infection. The prevalence of non-conservative mexZ mutations was 0%, 33% and 65% in children with new infection, CI children and CI adults, respectively. The same trend was seen in the ratio of non-conservative to non-synonymous mexZ mutations. Of isolates with non-conservative mexZ mutations, 59% were amikacin-resistant compared with 18% of isolates with non-synonymous mutations. The doubling rate of amikacin resistance and non-conservative mexZ mutations was approximately 5 years. Conclusions P. aeruginosa mexZ mutations undergo positive selection resulting in increased mexY mRNA expression and amikacin resistance and likely play a role in bacterial adaption in the CF lung.

The relationship between sweat chloride levels and mortality in cystic fibrosis varies by individual genotype

RATIONALE The association between CFTR genotype, sweat chloride and mortality has been inconsistent, but no previous analyses have examined the association stratified by individual genotypes. OBJECTIVES To evaluate the genotype-specific association between sweat chloride and mortality. METHODS The CFF Patient Registry was assessed and included all patients in the registry between 1996 and 2012 with at least one F508del allele. We excluded patients without a documented genotype or plausible sweat chloride level. The primary outcome was time to mortality during the observation period. We examined 15 genotypes using the three most prevalent alleles in each of 5 classes. We compared subgroups of sweat chloride using Kaplan-Meier curves, log-rank tests, and multivariable Cox PH models. The overall predictive value of sweat chloride on mortality was assessed using area under the receiver operating characteristic curves. MEASUREMENTS AND MAIN RESULTS 18,893 subjects met inclusion criteria. Sweat chloride distribution was similar across genotypes in patients with class 1 mutations, but was significantly different across genotypes in mutation classes 2-5. The R117H/F508del genotype patients demonstrated an association between sweat chloride and mortality (HR: 1.32 for every 10mmol/L increase in sweat chloride [95% CI 1.12-1.54]. There were also significant associations in patients with F508del/F508del, I507del/F508del, G551D/F508del and 2789+5G→A/F508del genotypes, though the clinical relevance for these genotypes is unclear. CONCLUSIONS There is significant variability in sweat chloride distribution across CFTR class 2-5 genotypes. The relationship between sweat chloride and mortality varies by genotype with a relatively strong relationship in R117H/F508del patients.

Polymyxin B Pharmacokinetics in Adult Cystic Fibrosis Patients

Polymyxin B pharmacokinetics (PK) in adults with cystic fibrosis (CF) are not well described. The goals of this pilot study were to identify a PK model for patients with CF receiving polymyxin B with exploration of covariate relationships of the PK parameters, to compare polymyxin B PK parameters in adults without CF, and to probe exposures associated with different dosing schemes through simulation.

Bronchiectasis: The dawn of a new era?

Bronchiectasis is a significant chronic health problem with major morbidity, mortality, and economic costs. However, despite the large burden of disease, much of the treatment for bronchiectasis is not guided by high-quality randomized controlled data but extrapolated from studies in patients with cystic fibrosis. Thankfully, in the past few years, we have had several high-quality publications in noncystic fibrosis bronchiectasis in the areas of nebulized antibiotic therapy and chronic oral macrolide therapy. This review focuses on these recent publications as they significantly change the approach toward patients with bronchiectasis, particularly those who have frequent exacerbations.

Pseudomonas aeruginosa Infection in Cystic Fibrosis: A Paradigm of Chronic Infection

Pseudomonas aeruginosa is a frequently encountered pathogen in multiple clinical settings. In acute infections, particularly in immunocompromised patients, the bacteria can increase expression of virulence factors such as type III secretion toxins with high mortality rates. In contrast, P. aeruginosa may cause chronic infections in patients with impaired local host defenses such as bronchiectasis. The best example of this is in patients with cystic fibrosis (CF) in which P. aeruginosa can reside for years to decades due to its ability to adapt in the CF lung. Changes by P. aeruginosa in patients with CF over time include the loss of virulence factors while also acquiring antibiotic resistance, making treatment difficult. This article reviews these adaptations in P. aeruginosa using the knowledge learned from study of patients with CF, which may also be applicable to other chronic lung diseases.