Chronic infection phenotypes of Pseudomonas aeruginosa are associated with failure of eradication in children with cystic fibrosis

Predictive modeling of antibiotic eradication therapy success for new-onset Pseudomonas aeruginosa pulmonary infections in children with cystic fibrosis

Chronic Pseudomonas aeruginosa (Pa) lung infections are the leading cause of mortality among cystic fibrosis (CF) patients; therefore, the eradication of new-onset Pa lung infections is an important therapeutic goal that can have long-term health benefits. The use of early antibiotic eradication therapy (AET) has been shown to clear the majority of new-onset Pa infections, and it is hoped that identifying the underlying basis for AET failure will further improve treatment outcomes. Here we generated machine learning models to predict AET outcomes based on pathogen genomic data. We used a nested cross validation design, population structure control, and recursive feature selection to improve model performance and showed that incorporating population structure control was crucial for improving model interpretation and generalizability. Our best model, controlling for population structure and using only 30 recursively selected features, had an area under the curve of 0.87 for a holdout test dataset. The top-ranked features were generally associated with motility, adhesion, and biofilm formation.

Comparison of Three Eradication Treatment Protocols for Pseudomonas Aeruginosa in Children and Adolescents with Cystic Fibrosis

BACKGROUND

Pseudomonas aeruginosa (Pa) continues to affect disease progression in cystic fibrosis (CF). However, the best eradication regimen remains unclear. This work compares three different antibiotic eradication regimens in pediatric CF: an administration according to a standard-operating procedure (SOP) order vs. administration outside of this order (ooSOP).

METHODS

This observational study includes all CF patients<18 years who received one of three Pa eradication treatments in the past eight years at our center: 1) inhaled high-dose tobramycin (Hi-TOBI), 2) inhaled colistin+oral ciprofloxacin (COL/Cip), 3) inhaled low-dose tobramycin+4 intravenous 14-day Pa active antibiotic treatments (lo-Tobra/IV). We compared eradication rates of the three treatment regimens performed according to the SOP-based order vs. ooSOP. Logistic regression analysis was performed to identify risk factors for eradication failure.

RESULTS

Performed according to SOP order, Hi-TOBI showed the greatest efficacy, followed by lo-Tobra/IV and finally COL/Cip, while ooSOP lo-Tobra/IV was most successful, followed by COL/Cip and Hi-TOBI. Previous Pa-infections and Pa-therapies along with age at CF diagnosis were risk factors for eradication failure.

CONCLUSION

Antibiotic treatment in SOP-based pre-defined order leads to significantly better eradication rates than individual modifications of the order of administration. A short course of inhalational high-dose Tobramycin is most successful at the first attempt. Prolonged antibiotic therapy seems to improve eradication after failed initial attempts.

Pseudomonas aeruginosa aggregation and Psl expression in sputum is associated with antibiotic eradication failure in children with cystic fibrosis

We previously demonstrated that P. aeruginosa isolates that persisted in children with cystic fibrosis (CF) despite inhaled tobramycin treatment had increased anti-Psl antibody binding in vitro compared to those successfully eradicated. We aimed to validate these findings by directly visualizing P. aeruginosa in CF sputum. This was a prospective observational study of children with CF with new-onset P. aeruginosa infection who underwent inhaled tobramycin eradication treatment. Using microbial identification passive clarity technique (MiPACT), P. aeruginosa was visualized in sputum samples obtained before treatment and classified as persistent or eradicated based on outcomes. Pre-treatment isolates were also grown as biofilms in vitro. Of 11 patients enrolled, 4 developed persistent infection and 7 eradicated infection. P. aeruginosa biovolume and the number as well as size of P. aeruginosa aggregates were greater in the sputum of those with persistent compared with eradicated infections (p < 0.01). The amount of Psl antibody binding in sputum was also greater overall (p < 0.05) in samples with increased P. aeruginosa biovolume. When visualized in sputum, P. aeruginosa had a greater biovolume, with more expressed Psl, and formed more numerous, larger aggregates in CF children who failed eradication therapy compared to those who successfully cleared their infection.

Opportunistic Pathogens in Cystic Fibrosis: Epidemiology and Pathogenesis of Lung Infection

Cystic fibrosis (CF) is one of the most common life-shortening genetic diseases in Caucasians. Due to abnormal accumulation of mucus, respiratory failure caused by chronic infections is the leading cause of mortality in this patient population. The microbiology of these respiratory infections includes a distinct set of opportunistic pathogens, including Pseudomonas aeruginosa, Burkholderia spp., Achromobacter spp., Stenotrophomonas maltophilia, anaerobes, nontuberculous mycobacteria, and fungi. In recent years, culture-independent methods have shown the polymicrobial nature of lung infections, and the dynamics of microbial communities. The unique environment of the CF airway predisposes to infections caused by opportunistic pathogens. In this review, we will highlight how the epidemiology and role in disease of these pathogens in CF differ from that in individuals with other medical conditions. Infectious diseases (ID) physicians should be aware of these differences and the specific characteristics of infections associated with CF.

A Model of Intracellular Persistence of Pseudomonas aeruginosa in Airway Epithelial Cells

Pseudomonas aeruginosa (P.a.) is a major human pathogen capable of causing chronic infections in hosts with weakened barrier functions and host defenses, most notably airway infections commonly observed in individuals with the genetic disorder cystic fibrosis (CF). While mainly described as an extracellular pathogen, previous in vitro studies have described the molecular events leading to P.a. internalization in diverse epithelial cell types. However, the long-term fate of intracellular P.a. remains largely unknown. Here, we developed a model allowing for a better understanding of long-term (up to 120 h) intracellular bacterial survival in the airway epithelial cell line BEAS-2B. Using a tobramycin protection assay, we characterized the internalization, long-term intracellular survival, and cytotoxicity of the lab strain PAO1, as well as clinical CF isolates, and conducted analyses at the single-cell level using confocal microscopy and flow cytometry techniques. We observed that infection at low multiplicity of infection allows for intracellular survival up to 120 h post-infection without causing significant host cytotoxicity. Finally, infection with clinical isolates revealed significant strain-to-strain heterogeneity in intracellular survival, including a high persistence phenotype associated with bacterial replication within host cells. Future studies using this model will further elucidate the host and bacterial mechanisms that promote P. aeruginosa intracellular persistence in airway epithelial cells, a potentially unrecognized bacterial reservoir during chronic infections.

Current and Emerging Therapies to Combat Cystic Fibrosis Lung Infections

The ultimate aim of any antimicrobial treatment is a better infection outcome for the patient. Here, we review the current state of treatment for bacterial infections in cystic fibrosis (CF) lung while also investigating potential new treatments being developed to see how they may change the dynamics of antimicrobial therapy. Treatment with antibiotics coupled with regular physical therapy has been shown to reduce exacerbations and may eradicate some strains. Therapies such as hypertonic saline and inhaled PulmozymeTM (DNase-I) improve mucus clearance, while modifier drugs, singly and more successfully in combination, re-open certain mutant forms of the cystic fibrosis transmembrane conductance regulator (CFTR) to enable ion passage. No current method, however, completely eradicates infection, mainly due to bacterial survival within biofilm aggregates. Lung transplants increase lifespan, but reinfection is a continuing problem. CFTR modifiers normalise ion transport for the affected mutations, but there is conflicting evidence on bacterial clearance. Emerging treatments combine antibiotics with novel compounds including quorum-sensing inhibitors, antioxidants, and enzymes, or with bacteriophages, aiming to disrupt the biofilm matrix and improve antibiotic access. Other treatments involve bacteriophages that target, infect and kill bacteria. These novel therapeutic approaches are showing good promise in vitro, and a few have made the leap to in vivo testing.

The role of Psl in the failure to eradicate Pseudomonas aeruginosa biofilms in children with cystic fibrosis

The exopolysaccharide Psl contributes to biofilm structure and antibiotic tolerance and may play a role in the failure to eradicate Pseudomonas aeruginosa from cystic fibrosis (CF) airways. The study objective was to determine whether there were any differences in Psl in P. aeruginosa isolates that were successfully eradicated compared to those that persisted, despite inhaled tobramycin treatment, in children with CF. Initial P. aeruginosa isolates were collected from children with CF undergoing eradication treatment, grown as biofilms and labeled with 3 anti-Psl monoclonal antibodies (Cam003/Psl0096, WapR001, WapR016) before confocal microscopy visualization. When grown as biofilms, P. aeruginosa isolates from children who failed antibiotic eradication therapy, had significantly increased Psl0096 binding compared to isolates from those who cleared P. aeruginosa. This was confirmed in P. aeruginosa isolates from the SickKids Eradication Cohort as well as the Early Pseudomonas Infection Control (EPIC) trial. Increased anti-Psl antibody binding was associated with bacterial aggregation and tobramycin tolerance. The biofilm matrix represents a potential therapeutic target to improve P. aeruginosa eradication treatment.

Failed eradication therapy of new onset Pseudomonas aeruginosa infections in cystic fibrosis children is associated with bacterial resistance to neutrophil functions

BACKGROUND

Antibiotics, such as inhaled tobramycin are used to eradicate new onset Pseudomonas aeruginosa (PA) infections in cystic fibrosis (CF) patients but frequently fail due to reasons poorly understood. We hypothesized that PA isolates' resistance to neutrophil antibacterial functions was associated with failed eradication in patients harboring those strains.

METHODS

We analyzed all PA isolates from a cohort of 39 CF children with new onset PA infections undergoing tobramycin eradication therapy, where N=30 patients had eradicated and N=9 patients had persistent infection. We characterized several bacterial phenotypes and measured the isolates' susceptibility to neutrophil antibacterial functions using in vitro assays of phagocytosis and intracellular bacterial killing.

RESULTS

PA isolates from persistent infections were more resistant to neutrophil functions, with lower phagocytosis and intracellular bacterial killing compared to those from eradicated infections. In multivariable analyses, in vitro neutrophil responses were positively associated with twitching motility, and negatively with mucoidy. In vitro neutrophil phagocytosis was a predictor of persistent infection following tobramycin even after adjustment for clinical risk factors.

CONCLUSIONS

PA isolates from new onset CF infection show strain-specific susceptibility to neutrophil antibacterial functions, and infection with PA isolates resistant to neutrophil phagocytosis is an independent risk factor for failed tobramycin eradication.

Factors influencing the acquisition and eradication of early Pseudomonas aeruginosa infection in cystic fibrosis

In recent years considerable improvements have been made in increasing the life expectancy of patients with cystic fibrosis. New highly effective modulator therapies targeting the underlying defect in the cystic fibrosis transmembrane conductance regulator protein are expected to enhance lifespan even further. However, chronic Pseudomonas aeruginosa pulmonary infections continue to threaten CF patient lung health and mortality rates. Early and aggressive antibiotic eradication therapies targeting P. aeruginosa are standard practice, but these eradication therapies fail in 10-40% of patients. The reasons for P. aeruginosa eradication failure remain unclear. Thus, this review summarizes the evidence to date for pseudomonal acquisition and eradication failure in the cystic fibrosis lung. A complex combination of host and bacterial factors are responsible for initial establishment of P. aeruginosa pulmonary infections. Moreover, host and pseudomonal factors, polymicrobial interactions, and antimicrobial limitations in relation to P. aeruginosa eradication therapy failure are summarized.

Pseudomonas aeruginosa Type III Secretion System Virulotypes and Their Association with Clinical Features of Cystic Fibrosis Patients

Purpose

Pseudomonas aeruginosa appears as the main pathogen in cystic fibrosis (CF) involved in recurrent pneumonia and pulmonary exacerbations. The type III secretion system (T3SS) is one of its main determinants of virulence and is associated with poor clinical progression and increased mortality. This study determined the relationship of clinical features of patients with CF and P. aeruginosa T3SS virulotypes.

Materials and Methods

From January 2018 to March 2019, P. aeruginosa were isolated from sputum and/or oropharyngeal swabs. T3SS markers (exoS, exoU, exoT and exoY) were detected by PCR. Clinical severity according to Shwachman-Kulckycki score and spirometry data were associated with T3SS virulotypes.

Results

A total of 49 patients had positive cultures for P. aeruginosa. T3SS virulence-related markers were detected as follows: exoS 97.9% (n=48), exoU 63.2% (n=31), exoT 95.9% (n=47) and exoY 97.9% (n=48). The prevalence of exoS⁺/exoU⁺ virulotype was higher than previously reported in CF settings, being detected in 61.2% of the evaluated isolates, present in 70% of intermittent infections and with a significantly higher frequency in cases of exacerbations. The presence of exoU in chronic infection was not associated with poor clinical results. In chronic infections, the exoS⁺/exoU⁻ virulotype prevailed (77.8%) and was associated to worse clinical results according to the Shwachman-Kulckycki score and spirometric.

Conclusion

Our findings revealed a high prevalence of the atypical exoS⁺/exoU⁺ virulotype among P. aeruginosa isolates from patients with CF, which was associated with intermittent infection and early clinical alterations, while the exoS⁺/exoU⁻ virulotype was associated with chronic infection and worse clinical results. Finally, the presented data highlight the relevance of T3SS virulence markers in the clinical progression and disease severity in CF patients.

Pseudomonas aeruginosa strain sharing in early infection among children with cystic fibrosis

BACKGROUND

We previously identified Pseudomonas aeruginosa isolates with characteristics typical of chronic infection in some early infections in children with Cystic Fibrosis (CF), suggesting these isolates may have been acquired from other patients. Our objective was to define the extent of P. aeruginosa strain sharing in early CF infections and its impact on antibiotic eradication treatment failure rates.

METHODS

We performed whole genome sequencing on isolates from early pediatric CF pulmonary infections and from comparator groups in the same hospital: chronic CF infection, sink drains, sterile site infections and asymptomatic carriage. Univariate logistic regression was used to assess factors associated with treatment failure.

RESULTS

In this retrospective observational study, 1,029 isolates were sequenced. The CF clones Strain B and Clone C were present. In 70 CF patients with early infections, 14 shared strains infected 29 (41%) patients over five years; 16% (n=14) of infections had mixed-strains. In the 70 children, approximately one third of shared strain infections were likely due to patient-to-patient transmission. Mixed-strain infections were associated with strain sharing (odds ratio 8.50; 95% confidence interval 2.2 - 33.4, P = 0.002). Strain sharing was not associated with antibiotic eradication treatment failure; however, nosocomial strain transmission was associated with establishment of chronic infection in a CF sibling pair.

CONCLUSIONS

Although early P. aeruginosa CF infection is thought to reflect acquisition of diverse strains from community reservoirs, we identified frequent early CF strain sharing which was associated with the presence of mixed-strains and instances of possible patient-to-patient transmission.

Microbiology of Cystic Fibrosis Airway Disease

Although survival of individuals with cystic fibrosis (CF) has been continuously improving for the past 40 years, respiratory failure secondary to recurrent pulmonary infections remains the leading cause of mortality in this patient population. Certain pathogens such as Pseudomonas aeruginosa, methicillin-resistant Staphylococcus aureus, and species of the Burkholderia cepacia complex continue to be associated with poorer clinical outcomes including accelerated lung function decline and increased mortality. In addition, other organisms such as anaerobes, viruses, and fungi are increasingly recognized as potential contributors to disease progression. Culture-independent molecular methods are also being used for diagnostic purposes and to examine the interaction of microorganisms in the CF airway. Given the importance of CF airway infections, ongoing initiatives to promote understanding of the epidemiology, clinical course, and treatment options for these infections are needed.

Identification of genomic loci associated with genotypic and phenotypic variation among Pseudomonas aeruginosa clinical isolates from pneumonia

In this work, a genotype-phenotype survey of a highly diversified Pseudomonas aeruginosa collection was conducted, aiming to detail pathogen-associated scenarios that clinicians face nowadays. Genetic relation based on RAPD-PCR of 705 isolates, retrieved from 424 patients and several clinical contexts, reported an almost isolate-specific molecular-pattern. Pneumonia-associated isolates HB13 and HB15, clustered in the same RAPD-PCR group, were selected to evaluate the genomic background underlying their contrasting antibiotic resistance and virulence. The HB13 genome harbors antibiotic-inactivating enzymes-coding genes (e.g. aac(3)-Ia, arr, bla_VIM-2) and single-nucleotide variations (SNVs) in antibiotic targets, likely accounting for its pan-resistance, whereas HB15 susceptibility correlated to predicted dysfunctional alleles. Isolate HB13 showed the unprecedented rhl-cluster absence and variations in other pathogen competitiveness contributors. Conversely, HB15 genome comprises exoenzyme-coding genes and SNVs linked to increased virulence. Secretome analysis identified signatures features with unknown function as potential novel pathogenic (e.g. a MATE-protein in HB13, a protease in HB15) and antibiotic resistance (a HlyD-like secretion protein in HB13) determinants. Detection of active prophages, proteases (including protease IV and alkaline metalloproteinase), a porin and a peptidase in HB15 highlights the secreted arsenal likely essential for its virulent behavior. The presented phenotype-genome association will contribute to the current knowledge on Pseudomonas aeruginosa pathogenomics.

Aerosolized Bovine Lactoferrin Counteracts Infection, Inflammation and Iron Dysbalance in A Cystic Fibrosis Mouse Model of Pseudomonas aeruginosa Chronic Lung Infection

Cystic fibrosis (CF) is a genetic disorder affecting several organs including airways. Bacterial infection, inflammation and iron dysbalance play a major role in the chronicity and severity of the lung pathology. The aim of this study was to investigate the effect of lactoferrin (Lf), a multifunctional iron-chelating glycoprotein of innate immunity, in a CF murine model of Pseudomonas aeruginosa chronic lung infection. To induce chronic lung infection, C57BL/6 mice, either cystic fibrosis transmembrane conductance regulator (CFTR)-deficient (Cftr^tm1UNCTgN(FABPCFTR)#Jaw) or wild-type (WT), were intra-tracheally inoculated with multidrug-resistant MDR-RP73 P. aeruginosa embedded in agar beads. Treatments with aerosolized bovine Lf (bLf) or saline were started five minutes after infection and repeated daily for six days. Our results demonstrated that aerosolized bLf was effective in significantly reducing both pulmonary bacterial load and infiltrated leukocytes in infected CF mice. Furthermore, for the first time, we showed that bLf reduced pulmonary iron overload, in both WT and CF mice. In particular, at molecular level, a significant decrease of both the iron exporter ferroportin and iron storage ferritin, as well as luminal iron content was observed. Overall, bLf acts as a potent multi-targeting agent able to break the vicious cycle induced by P. aeruginosa, inflammation and iron dysbalance, thus mitigating the severity of CF-related pathology and sequelae.

Filamentous bacteriophages are associated with chronic Pseudomonas lung infections and antibiotic resistance in cystic fibrosis

Filamentous bacteriophage (Pf phage) contribute to the virulence of Pseudomonas aeruginosa infections in animal models, but their relevance to human disease is unclear. We sought to interrogate the prevalence and clinical relevance of Pf phage in patients with cystic fibrosis (CF) using sputum samples from two well-characterized patient cohorts. Bacterial genomic analysis in a Danish longitudinal cohort of 34 patients with CF revealed that 26.5% (n = 9) were consistently Pf phage positive. In the second cohort, a prospective cross-sectional cohort of 58 patients with CF at Stanford, sputum qPCR analysis showed that 36.2% (n = 21) of patients were Pf phage positive. In both cohorts, patients positive for Pf phage were older, and in the Stanford CF cohort, patients positive for Pf phage were more likely to have chronic P. aeruginosa infection and had greater declines in pulmonary function during exacerbations than patients negative for Pf phage presence in the sputum. Last, P. aeruginosa strains carrying Pf phage exhibited increased resistance to antipseudomonal antibiotics. Mechanistically, in vitro analysis showed that Pf phage sequesters these same antibiotics, suggesting that this mechanism may thereby contribute to the selection of antibiotic resistance over time. These data provide evidence that Pf phage may contribute to clinical outcomes in P. aeruginosa infection in CF.

"Pathogen Eradication" and "Emerging Pathogens": Difficult Definitions in Cystic Fibrosis

Infection is a common complication of cystic fibrosis (CF) airway disease. Current treatment approaches include early intervention with the intent to eradicate pathogens in the hope of delaying the development of chronic infection and the chronic use of aerosolized antibiotics to suppress infection. The use of molecules that help restore CFTR (cystic fibrosis transmembrane conductance regulator) function, modulate pulmonary inflammation, or improve pulmonary clearance may also influence the microbial communities in the airways. As the pipeline of these new entities continues to expand, it is important to define when key pathogens are eradicated from the lungs of CF patients and, equally important, when new pathogens might emerge as a result of these novel therapies.

Presence of pldA and exoU in mucoid Pseudomonas aeruginosa is associated with high risk of exacerbations in non-cystic fibrosis bronchiectasis patients

OBJECTIVES

To explore the association between the virulence genes exoU and pldA in isolated mucoid Pseudomonas aeruginosa and the clinical outcomes of patients with non-cystic fibrosis (CF) bronchiectasis.

METHODS

A prospective observational cohort study was performed in the Shanghai Pulmonary Hospital from October 2012 to January 2015. We consecutively enrolled all non-CF bronchiectasis patients with mucoid P. aeruginosa isolates obtained from bronchoalveolar lavage fluid or sputum. The exposure variable was the presence of virulence gene, exoU or pldA, in the strains. The primary outcome was exacerbation of bronchiectasis. Logistic regression analysis was performed to evaluate the association between virulence genes and exacerbation.

RESULTS

The final analysis included 147 patients (mean (SD) age, 57.86 (11.43) years, 101 female subjects) with median (interquartile range) follow-up of 18 (13-26) months. The following factors were relative to exacerbations: body mass index ≤18.5 kg/m² (odds ratio (OR) = 5.05; 95% confidence interval (CI), 1.37-18.57), length of stay ≥8 days (OR = 2.65; 95% CI, 1.14-6.19) and positive for either virulence gene (OR = 6.80; 95% CI, 1.47-31.37). The gene-positive group had more exacerbations per year (mean 2.37, SD 2.10, n = 33 vs. mean 0.79, SD 0.83, n = 114) and a higher proportion of patients with exacerbation (31/33, 93.94% vs. 74/114, 64.91%). The proportion of patients being exoU or pldA positive increased as the exacerbation frequency of bronchiectasis increased.

CONCLUSIONS

The virulence genes exoU and pldA in mucoid P. aeruginosa are significant risk factors for exacerbations in patients with non-CF bronchiectasis.

Early detection using qPCR of Pseudomonas aeruginosa infection in children with cystic fibrosis undergoing eradication treatment

BACKGROUND

Infection with Pseudomonas aeruginosa (Pa) with a chronic phenotype is associated with antibiotic eradication therapy (AET) failure. Our objective was to determine whether higher levels of Pa (detected using qPCR) prior to culture positivity were associated with AET failure in pediatric CF patients.

METHODS

Pa-specific qPCR was performed on stored sputa prior to culture positivity in pediatric CF patients with new-onset culture-positive Pa infections undergoing AET with a 28-day course of tobramycin-inhaled solution (TIS). DNA concentrations were compared in patients in whom AET was successful (Eradicated) to those with persistently positive sputum cultures (Persistent).

RESULTS

Forty-seven patients were included. AET was successful in 32 cases (68%), but failed in 15 cases (32%). Median sputum Pa-specific DNA concentration preceding the positive sputum culture was 2.2 × 10^-6 μg/mL in Eradicated cases compared to 3 × 10^-5 μg/mL in Persistent cases (p = 0.14). There was no significant difference in DNA concentration in the last sputum sample prior to culture positivity, nor in maximal DNA values. There was also no difference in sputum Pa DNA concentrations in patients who had a mucoid (compared to non-mucoid) Pa infection.

CONCLUSIONS

Pediatric CF patients with new-onset Pa infections have detectable Pa-specific DNA in the year preceding a positive culture, however, there is no significant difference in Pa DNA concentrations between patients in whom AET is successful compared to those in whom it fails. Therefore, early molecular detection of Pa may not lead to improved eradication success rates.

Longitudinal development of initial, chronic and mucoid Pseudomonas aeruginosa infection in young children with cystic fibrosis

BACKGROUND

While the emergence of chronic and mucoid Pseudomonas aeruginosa (Pa) infection are both associated with poorer outcomes among CF patients, their relationship is poorly understood. We examined the longitudinal relationship of incident, chronic and mucoid Pa in a contemporary, young CF cohort in the current era of Pa eradication therapy.

METHODS

This retrospective cohort was comprised of patients in the U.S. CF Foundation Patient Registry born 2006-2015, diagnosed before age 2, and with at least 3 respiratory cultures annually. Incidence and age-specific prevalence of Pa infection stages (initial and chronic [≥ 3Pa+cultures in prior year]) and of mucoid Pa were summarized. Transition times and the interaction between Pa stage and acquisition of mucoid Pa were examined via Cox models.

RESULTS

Among the 5592 CF patients in the cohort followed to a mean age of 5.5years, 64% (n=3580) acquired Pa. Of those, 13% (n=455) developed chronic Pa and 17% (n=594) cultured mucoid Pa. Among those with mucoid Pa, 36% (211/594) had it on their first recorded Pa+culture, while mucoid Pa emerged at or after entering the chronic stage in 12% (73/594). Mucoidy was associated with significantly increased risk of transition to chronic Pa infection (HR=2.59, 95% CI 2.11, 3.19).

CONCLUSIONS

Two-thirds of early-diagnosed young children with CF acquired Pa during a median 5.6years of follow up, among whom 13% developed chronic Pa and 17% acquired mucoid Pa. Contrary to our hypothesis, 87% of young children who developed mucoid Pa did so before becoming chronically infected.

Staphylococcus aureus interaction with Pseudomonas aeruginosa biofilm enhances tobramycin resistance

Antimicrobial resistance is a significant threat to the treatment of infectious disease. Multiple mechanisms of resistance to different classes of antibiotics have been identified and well-studied. However, these mechanisms are studied with bacteria in isolation, whereas often, infections have a polymicrobial basis. Using a biofilm slide chamber model, we visualized the formation and development of clinical Pseudomonas aeruginosa biofilms in the presence of secreted Staphylococcus aureus exoproducts, two bacteria that commonly co-infect pediatric patients with cystic fibrosis. We showed that, over time, certain isolates of P. aeruginosa can form different biofilm architecture in the presence of S. aureus exoproducts. We further determined that this interaction was dependent on Psl produced by P. aeruginosa and staphylococcal protein A from S. aureus. Importantly, we identified a mechanism of antibiotic resistance to tobramycin that is dependent on the polymicrobial interactions between these two bacteria. This interaction occurred in isolates of P. aeruginosa recovered from children with cystic fibrosis who failed to clear P. aeruginosa following inhaled tobramycin treatment.

The interaction between two different bacterial species can enhance the antibiotic resistance of biofilms. Resistance to antimicrobial therapy is usually studied using individual bacterial species, but many infections involve more than one species. Researchers in Canada, led by Trevor Beaudoin at The Hospital for Sick Children in Toronto, studied the effect of products secreted by Staphylococcus aureus bacteria on biofilms of Pseudomonas aeruginosa. They worked with biofilms that had resisted treatment, isolated from patients with cystic fibrosis. The co-infection altered the biofilm structure and increased its resistance to the antibiotic tobramycin. The effect depended on bacterial aggregation stimulated by the interaction between a large carbohydrate from P. aeruginosa and a protein secreted by S. aureus. The research highlights the need to study bacterial interactions to understand and treat infections involving different bacteria.

Cystic fibrosis year in review 2016

In this article, we highlight cystic fibrosis (CF) research and case reports published in Pediatric Pulmonology during 2016. We also include articles from a variety of journals that are thematically related to these articles, or are of special interest to clinicians.

Anti-Pseudomonas aeruginosa IgG antibodies and chronic airway infection in bronchiectasis

BACKGROUND

Identification of chronic Pseudomonas aeruginosa (PA) infection is important in the management of bronchiectasis, but requires repeated sputum sampling. We hypothesized that serum anti-PA IgG antibodies could diagnose chronic PA infection at a single visit.

METHODS

Clinically stable bronchiectasis patients were studied prospectively. Chronic PA infection was defined as 2 or more positive sputum samples at least 3 months apart and/or failure to clear PA following eradication treatment. Baseline serum anti-PA IgG was determined by a validated ELISA kit.

RESULTS

A total of 408 patients were included. Sixty of them (14.7%) had chronic PA infection and had higher anti-PA IgG levels (median 6.2 vs. 1.3 units, p < 0.001). Antibody levels showed direct significant correlations with exacerbation frequency, the bronchiectasis severity index and sputum inflammatory markers. Fifty-seven patients with chronic PA infection had a positive test, giving 95% sensitivity, 74.4% specificity and AUROC of 0.87. During follow-up, 38 patients had a new PA isolation. Eradication at 12 months was achieved in 89.5% of subjects with a negative antibody test and 15.8% of patients with a positive test.

CONCLUSIONS

Anti-PA IgG test is highly accurate to detect chronic PA infection in bronchiectasis patients. In addition, it may be a marker of disease severity and treatment response.

Effectiveness of a stepwise Pseudomonas aeruginosa eradication protocol in children with cystic fibrosis

INTRODUCTION

Antibiotic eradication therapy (AET) for initial Pseudomonas aeruginosa (Pa) infection is standard of care in children with cystic fibrosis (CF), but information is limited on treatment for patients who fail initial AET. The aim of this study was to evaluate the effectiveness of a multi-step protocol for AET for new-onset Pa infections in children with CF.

METHODS

A three-step AET protocol which includes: (step 1) 28days of tobramycin inhalation solution (TIS) for new-onset Pa infection; (step 2) a second course of TIS for patients with positive respiratory tract culture after step 1; (step 3) 14days of intravenous antibiotics followed by 28days of TIS for patients with a subsequent positive culture. We conducted a retrospective review of all pediatric CF patients who underwent the eradication protocol between January 2010 and December 2015. The success rate of each step and of the overall protocol was recorded.

RESULTS

During the study period, 128 patients had a total of 213 new-onset Pa infections. Of 195 asymptomatic episodes, 150 (76.9%, 95% CI 70.4; 82.6) cleared after step 1 and 12 cleared after step 2 (33.3% (95% CI 18.6; 50.9) stepwise success rate and 87.1% (95% CI 77.1; 88.1) cumulative success rate). Intravenous antibiotics followed by 28days of TIS were administered in 24 episodes; this was successful in 10 episodes (41.7%; 95% CI 22.1; 63.4). The regimen in asymptomatic patients failed in fourteen episodes (7.5%; 95% CI 4.2; 12.3) then considered chronically infected with Pa. Overall, the cumulative success rate of the asymptomatic arm was 88.2% (95% CI 82.8; 92.4).

CONCLUSION

The first step of the AET protocol led to the greatest eradication success. Subsequent eradication attempts have a success rate below 50%. Prospective studies of eradication protocols for this population are needed to determine the most effective treatment strategy.

Visualizing the Effects of Sputum on Biofilm Development Using a Chambered Coverglass Model

Biofilms consist of groups of bacteria encased in a self-secreted matrix. They play an important role in industrial contamination as well as in the development and persistence of many health related infections. One of the most well described and studied biofilms in human disease occurs in chronic pulmonary infection of cystic fibrosis patients. When studying biofilms in the context of the host, many factors can impact biofilm formation and development. In order to identify how host factors may affect biofilm formation and development, we used a static chambered coverglass method to grow biofilms in the presence of host-derived factors in the form of sputum supernatants. Bacteria are seeded into chambers and exposed to sputum filtrates. Following 48 hr of growth, biofilms are stained with a commercial biofilm viability kit prior to confocal microscopy and analysis. Following image acquisition, biofilm properties can be assessed using different software platforms. This method allows us to visualize key properties of biofilm growth in presence of different substances including antibiotics.

Determinants for persistence of Pseudomonas aeruginosa in hospitals: interplay between resistance, virulence and biofilm formation

Pseudomonas aeruginosa (Pa) is one of the major bacterial pathogens causing nosocomial infections. During the past few decades, multidrug-resistant (MDR) and extensively drug-resistant (XDR) lineages of Pa have emerged in hospital settings with increasing numbers. However, it remains unclear which determinants of Pa facilitated this spread. A total of 211 clinical XDR and 38 susceptible clinical Pa isolates (nonXDR), as well as 47 environmental isolates (EI), were collected at the Heidelberg University Hospital. We used RAPD PCR to identify genetic clusters. Carriage of carbapenamases (CPM) and virulence genes were analyzed by PCR, biofilm formation capacity was assessed, in vitro fitness was evaluated using competitive growth assays, and interaction with the host's immune system was analyzed using serum killing and neutrophil killing assays. XDR isolates showed significantly elevated biofilm formation (p < 0.05) and higher competitive fitness compared to nonXDR and EI isolates. Thirty percent (62/205) of the XDR isolates carried a CPM. Similarities in distribution of virulence factors, as well as biofilm formation properties, between CPM+ Pa isolates and EI and between CPM- and nonXDR isolates were detected. Molecular typing revealed two distinct genetic clusters within the XDR population, which were characterized by even higher biofilm formation. In contrast, XDR isolates were more susceptible to the immune response than nonXDR isolates. Our study provides evidence that the ability to form biofilms is an outstanding determinant for persistence and endemic spread of Pa in the hospital setting.

Antimicrobial susceptibility of microorganisms isolated from sputum culture of patients with cystic fibrosis: Methicillin-resistant Staphylococcus aureus as a serious concern

INTRODUCTION

Infection is a major cause of morbidity and mortality in patients with cystic fibrosis (CF). Antimicrobial resistance of the bacterial spp. particularly methicillin resistance in Staphylococcus aureus has caused a lot of attention. The aim of this study was to describe the prevalence of S. aureus, Pseudomonas aeruginosa and Burkholderia cepacia-complex as well as their antimicrobial susceptibility patterns in CF patients in an Iranian referral pediatrics Hospital.

MATERIAL AND METHODS

From March 2011 until February 2012, 172 samples were collected at the Children Medical Center (CMC), an Iranian referral hospital in Tehran, Iran. Sputum specimens were cultured for the following bacterial pathogens: P. aeruginosa, S. aureus, B. cepacia complex. Antimicrobial susceptibility was performed according to the Clinical Laboratory Standards Institute recommendations.

RESULTS

In our study, 54% of the patients (n = 93) harbored at least once S. aureus, 30% (n = 52) P. aeruginosa, and 2% (n = 3) Burkholderia cepacia. In 40 patients (23%), none of these organisms was grown. An increasing colonization rate of P. aeruginosa in the second decade of life was found. In contrast, the colonization rate of S. aureus was constant in both decades of life. Methicillin resistant S. aureus (MRSA) was detected in 40 isolates (43%). Among MRSA, no resistance against vancomycin, linezolid and quinupristin/dalfopristin occurred. The susceptibility of P. aeruginosa isolates to meropenem, imipenem, doripenem, levofloxacin and polymixin B were more than 90%.

CONCLUSION

The prevalence of MRSA has been rising. Since its impact on clinical outcomes, optimal prevention and treatment strategies are unclear, further studies to expand the knowledge about the infection control strategies and MRSA treatment are highly recommended.

Aerosolized bovine lactoferrin reduces neutrophils and pro-inflammatory cytokines in mouse models of Pseudomonas aeruginosa lung infections

Lactoferrin (Lf), an iron-chelating glycoprotein of innate immunity, produced by exocrine glands and neutrophils in infection/inflammation sites, is one of the most abundant defence molecules in airway secretions. Lf, a pleiotropic molecule, exhibits antibacterial and anti-inflammatory functions. These properties may play a relevant role in airway infections characterized by exaggerated inflammatory response, as in Pseudomonas aeruginosa lung infection in cystic fibrosis (CF) subjects. To verify the Lf role in Pseudomonas aeruginosa lung infection, we evaluated the efficacy of aerosolized bovine Lf (bLf) in mouse models of P. aeruginosa acute and chronic lung infections. C57BL/6NCrl mice were challenged with 10⁶ CFUs of P. aeruginosa PAO1 (acute infection) or MDR-RP73 strain (chronic infection) by intra-tracheal administration. In both acute and chronic infections, aerosolized bLf resulted in nonsignificant reduction of bacterial load but significant decrease of the neutrophil recruitment and pro-inflammatory cytokine levels. Moreover, in chronic infection the bLf-treated mice recovered body weight faster and to a higher extent than the control mice. These findings add new insights into the benefits of bLf as a mediator of general health and its potential therapeutic applications.

Engineered cationic antimicrobial peptide (eCAP) prevents Pseudomonas aeruginosa biofilm growth on airway epithelial cells

OBJECTIVES

Chronic infections with the opportunistic pathogen Pseudomonas aeruginosa are responsible for the majority of the morbidity and mortality in patients with cystic fibrosis (CF). While P. aeruginosa infections may initially be treated successfully with standard antibiotics, chronic infections typically arise as bacteria transition to a biofilm mode of growth and acquire remarkable antimicrobial resistance. To address the critical need for novel antimicrobial therapeutics that can effectively suppress chronic bacterial infections in challenging physiological environments, such as the CF lung, we have rationally designed a de novo engineered cationic antimicrobial peptide, the 24-residue WLBU2, with broad-spectrum antibacterial activity for pan-drug-resistant P. aeruginosa in liquid culture. In the current study, we tested the hypothesis that WLBU2 also prevents P. aeruginosa biofilm growth.

METHODS

Using abiotic and biotic biofilm assays, co-culturing P. aeruginosa with polarized human airway epithelial cells, we examined the ability of WLBU2 to prevent biofilm biogenesis alone and in combination with currently used antibiotics.

RESULTS

We observed a dose-dependent reduction in biofilm growth on an abiotic surface and in association with CF airway epithelial cells. WLBU2 prevented P. aeruginosa biofilm formation when co-cultured with mucus-producing primary human CF airway epithelial cells and using CF clinical isolates of P. aeruginosa, even at low pH and high salt conditions that mimic the CF airway. When used in combination, WLBU2 significantly increases killing by the commonly used antibiotics tobramycin, ciprofloxacin, ceftazidime and meropenem.

CONCLUSIONS

While other studies have demonstrated the ability of natural and synthetic antimicrobial peptides to prevent abiotic bacterial biofilm formation, the current studies for the first time demonstrate the effective peptide treatment of a biotic bacterial biofilm in a setting similar to the CF airway, and without negative effects on human airway epithelial cells, thus highlighting the unique potential of this engineered cationic antimicrobial peptide for treatment of human respiratory infections.