In search of the best method to detect carriage of carbapenem-resistant Pseudomonas aeruginosa in humans: a systematic review

BACKGROUND

Detection of carbapenem-resistant Pseudomonas aeruginosa (CR-PA) in humans is important to prevent transmission. However, the most optimal culture method to detect CR-PA is unknown. This systematic review aims to determine which culture method is most sensitive and which culture methods are used to detect CR-PA in humans. Second, to establish the most feasible culture method taking into account the turnaround time (TAT), and third, to provide an overview of the sampling sites used to detect carriage.

METHODS

We systematically searched the electronic databases Embase, Medline Ovid, Cochrane, Scopus, CINAHL, and Web of Science until January 27, 2023. All diagnostic accuracy studies comparing two or more culture methods to detect CR-PA and recent outbreak or surveillance reports on CR-PA carriage or infection in humans, which describe culture methods and their results, were eligible for inclusion. We used QUADAS-2 guideline for diagnostic accuracy studies and the STROBE or ORION guideline for outbreak-surveillance studies to assess the risk of bias.

RESULTS

Six diagnostic accuracy studies were included. An enrichment broth was found to increase the detection of CR-PA. Using an enrichment broth extended the TAT by 18-24 h, yet selective media could reduce the TAT by 24 h compared to routine media. In total, 124 outbreak-surveillance studies were included, of which 17 studies with surveillance samples and 116 studies with clinical samples. In outbreak-surveillance studies with surveillance samples, perianal, rectal swabs or stools were the most common sampling site/specimen (13/17, 76%). A large variety was observed in whether and which kind of enrichment broth and selective media were used.

CONCLUSIONS

We found a benefit of using an enrichment step prior to inoculation of the material onto selective media for the detection of CR-PA. More research is needed to determine the most sensitive sampling site and culture method.

TRAIL REGISTRATION

This study was registered in the PROSPERO International prospective register of systematic reviews (registration number: CRD42020207390, http://www.crd.york.ac.uk/PROSPERO/display_record.asp?ID=CRD42020207390 ).

A Novel Method to Assess Antimicrobial Susceptibility in Commensal Oropharyngeal Neisseria-A Pilot Study

Commensal Neisseria provide a reservoir of resistance genes that can be transferred to the pathogens Neisseria gonorrhoeae and N. meningitidis in the human oropharynx. Surveillance programs are thus needed to monitor resistance in oropharyngeal commensal Neisseria, but currently the isolation and antimicrobial susceptibility testing of these commensals is laborious, complex and expensive. In addition, the posterior oropharyngeal/tonsillar swab, which is commonly used to sample oropharyngeal Neisseria, is poorly tolerated by many individuals. We evaluated an alternative non-invasive method to isolate oropharyngeal commensal Neisseria and to detect decreased susceptibility to azithromycin using selective media (LBVT.SNR) with and without azithromycin (2 µg/mL). In this pilot study, we compared paired posterior oropharyngeal/tonsillar swabs and oral rinse-and-gargle samples from 10 participants and demonstrated that a similar Neisseria species diversity and number of colonies were isolated from both sample types. Moreover, the proportion of Neisseria colonies that had a decreased susceptibility to azithromycin was similar in the rinse samples compared to the swabs. This pilot study has produced encouraging data that a simple protocol of oral rinse-and-gargle and culture on plates selective for commensal Neisseria with and without a target antimicrobial can be used as a surveillance tool to monitor antimicrobial susceptibility in commensal oropharyngeal Neisseria. Larger studies are required to validate these findings.

Antimicrobial susceptibility of multidrug-resistant Pseudomonas aeruginosa isolated from drinking water and hospitalized patients in Jordan

Pseudomonas aeruginosa (P. aeruginosa) is an important environmental, opportunistic and nosocomial pathogen with a significant threat to public health. The objectives of this study were to determine the in vitro antimicrobial susceptibility patterns of, and antibiotic drug combinations with synergistic effects against P. aeruginosa isolated from drinking water and hospitalized patients in Jordan. A total of 16 P. aeruginosa isolates were obtained from hospitalized patients and 15 were isolated from bottled drinking water were used in the study. Bacterial isolation and identification was performed using routine microbiological methods and confirmed using PCR technique targeting the 16S rDNA gene. The antimicrobial susceptibility patterns were determined by measuring the minimum inhibitory concentration (MIC) using the 2-fold microdilution method. Synergy interaction between various antimicrobials was determined using the checkerboard method and fractional inhibitory concentration index (FICI). The majority of water isolates were sensitive to gentamicin (93.3%), ticarcillin (86.7%) and ciprofloxacin, levofloxacin, amikacin, colistin, piperacillin, azlocillin, aztreonam, ceftazidime and imipenem (100% each). All water isolates (100%) were resistant to amoxicillin, oxytetracycline and doxycycline (93.3% and 86.7, respectively). For the clinical isolates, all (100%) were sensitive to ceftazidime, 81.3% were sensitive to aztreonam, while 62.5% were sensitive to ciprofloxacin, levofloxacin, gentamicin, amikacin, colistin, piperacillin, ticracillin, azlocillin, and imipenem. All clinical isolates (100%) were resistant to oxytetracycline, doxycycline and amoxicillin. Analysis of the checkerboard synergy assay of multi-drug resistant isolates (n=26) showed significant synergism (P ≤ 0.05) when ciprofloxacin or gentamicin were included in the combination. There were no significant differences in synergistic activity between ciprofloxacin and levofloxacin when combined with other antimicrobial agents of the beta-lactams or aminoglycosides classes. There were no significant differences in the synergistic activities between beta lactams - aminoglycoside and beta lactams - fluoroquinolone combinations. Results of this study indicate an alarming widespread presence of multidrug-resistant P. aeruginosa associated with chronic suppurative infections in hospitalized patients and apparently clean drinking water in Jordan. Treatment of clinical suppurative lesions must be based on culture and in vitro susceptibility testing using potent antimicrobial combinations to avoid emergence of resistant strains and to improve the clinical outcome of treated patients.

Comparison of the effects of Lactobacillus plantarum versus imipenem on infected burn wound healing

Background: Infection of burn wounds is one of the most important problems in the world. Lactobacillus plantarum is known for burn wound healing because of the immunomodulatory and anti-microbial roles. This study was performed to compare the effects of L. plantarum and imipenem - alone and in combination - on infected burn wound healing. Methods: Burn wounds were experimentally induced on 50 rats in three test groups (germ and supernatant of L. plantarum ) and two control groups (n=10 each) and were inoculated with Pseudomonas aeruginosa. During a 14-day period, wounds in all groups were daily treated topically. The data were analyzed using one-way analysis of variance followed by Tukey-Kramer and LSD. A p-value of < 0.05 was considered as statistically significant. Results: The mean size of the wound on day 14 after the treatment in the probiotic group was significantly lower than the control and the supernatant treated groups (p<0.05). The percentage of wound healing was significantly higher in the probiotic pellet treated group compared to the imipenem and the supernatant groups (by Anova test: 69.58%, p=0.022). The mean leukocyte count in the probiotic pellet group (12110) and supernatant group (13650) was significantly higher than the imipenem group (7670) (p=0.002 and 0.001, respectively). Wound cultures revealed that the percentage of cases where the pathogens had no growth was significantly different among the comparison groups. In all three test groups, P. aeruginosa was completely eliminated in comparison to the positive control group (p<0.05). Conclusion: The results of our study showed that L. plantarum and its by-products promote wound healing and can be used as an alternative to antibiotics to treat ulcer infections caused by resistant bacteria.

A Selective, Dual Emission β-Alanine Aminopeptidase Activated Fluorescent Probe for the Detection of Pseudomonas aeruginosa, Burkholderia cepacia, and Serratia marcescens

Selective detection of β-alanyl aminopeptidase (BAP)-producing Pseudomonas aeruginosa, Serratia marcescens, and Burkholderia cepacia was achieved by employing the blue-to-yellow fluorescent transition of a BAP-specific enzyme substrate, 3-hydroxy-2-(p-dimethylaminophenyl)flavone derivative, incorporating a self-immolative linker to β-alanine. Upon cellular uptake and accumulation of the substrate by viable bacterial colonies, blue fluorescence was generated, while hydrolysis of the N-terminal peptide bond by BAP resulted in the elimination of the self-immolative linker and the restoration of the original fluorescence of the flavone derivative.

Clinical implications of Pseudomonas aeruginosa location in the lungs of patients with cystic fibrosis

WHAT IS KNOWN AND OBJECTIVE

Pseudomonas aeruginosa is the leading cause of lung infection in patients with cystic fibrosis (CF) and is associated with significant morbidity and mortality. Antibiotics are regarded as the foundational pharmacological treatment for the suppressive management of chronic P. aeruginosa infections and to eradicate the first infection by P. aeruginosa. Inhalation remains a preferred route for drug administration, providing direct access to the site of infection while minimizing systemic side effects. Effective suppressive management of P. aeruginosa infections, however, requires an understanding of the location of the bacteria in the lungs and consideration of the factors that could limit access of the inhaled antibiotic to the infected area. This review provides a systematic assessment of the scientific literature to gain insight into the location of P. aeruginosa in the lungs of patients with CF and its clinical implications. The characteristics of antibiotic inhalation systems are also discussed in this context.

METHODS

We reviewed evidence-based literature from both human and animal studies in which P. aeruginosa lung location was reported. Relevant publications were identified through a screening strategy and summarized by reported P. aeruginosa location.

RESULTS AND DISCUSSION

Most areas of the conductive and respiratory zones of the lungs are susceptible to P. aeruginosa colonization. Deposition of an inhaled antibiotic is dependent on the device and formulation characteristics, as well as the ability of the patient to generate sufficient inhaled volume. As patients with CF often experience a decline in lung function, the challenge is to ensure that the inhaled antibiotic can be delivered throughout the bronchial tree.

WHAT IS NEW AND CONCLUSION

An effective drug delivery system that can target P. aeruginosa in both the respiratory and conductive zones is required. The chosen inhalation device should also offer a drug formulation that can be quickly and effectively delivered to specific lung locations, with minimal inspiratory effort from the patient.

Pharmacokinetic and pharmacodynamic implications in inhalable antimicrobial therapy

Inhaled antimicrobials provide a promising alternative to the systemically delivered drugs for the treatment of acute and chronic lung infections. The delivery of antimicrobials via inhalation route decreases the systemic exposure while increasing the local concentration in the lungs, enabling the use of antimicrobials with severe systemic side effects. The inhalation route of administration has several challenges in pharmacokinetic (PK) and pharmacodynamic (PD) assessments. This review discusses various issues that need to be considered during study, data analysis, and interpretation of PK and PD of inhaled antimicrobials. Advancements overcoming the challenges are also discussed.

Lung transplantation for cystic fibrosis: results, indications, complications, and controversies

Survival in patients with cystic fibrosis (CF) has improved dramatically over the past 30 to 40 years, with mean survival now approximately 40 years. Nonetheless, progressive respiratory insufficiency remains the major cause of mortality in CF patients, and lung transplantation (LT) is eventually required. Timing of listing for LT is critical, because up to 25 to 41% of CF patients have died while awaiting LT. Globally, approximately 16.4% of lung transplants are performed in adults with CF. Survival rates for LT recipients with CF are superior to other indications, yet LT is associated with substantial morbidity and mortality (∼50% at 5-year survival rates). Myriad complications of LT include allograft failure (acute or chronic), opportunistic infections, and complications of chronic immunosuppressive medications (including malignancy). Determining which patients are candidates for LT is difficult, and survival benefit remains uncertain. In this review, we discuss when LT should be considered, criteria for identifying candidates, contraindications to LT, results post-LT, and specific complications that may be associated with LT. Infectious complications that may complicate CF (particularly Burkholderia cepacia spp., opportunistic fungi, and nontuberculous mycobacteria) are discussed.

Inhaled antibiotics: dry or wet?

Dry powder inhalers (DPIs) delivering antibiotics for the suppressive treatment ofPseudomonas aeruginosain cystic fibrosis patients were developed recently and are now increasingly replacing time-consuming nebuliser therapy. Noninferiority studies have shown that the efficacy of inhaled tobramycin delivered by DPI was similar to that of wet nebulisation. However, there are many differences between inhaled antibiotic therapy delivered by DPI and by nebuliser. The question is whether and to what extent inhalation technique and other patient-related factors affect the efficacy of antibiotics delivered by DPI compared with nebulisers. Health professionals should be aware of the differences between dry and wet aerosols, and of patient-related factors that can influence efficacy, in order to personalise treatment, to give appropriate instructions to patients and to better understand the response to the treatment after switching.

In this review, key issues of aerosol therapy are discussed in relation to inhaled antibiotic therapy with the aim of optimising the use of both nebulised and DPI antibiotics by patients. An example of these issues is the relationship between airway generation, structural lung changes and local concentrations of the inhaled antibiotics. The pros and cons of dry and wet modes of delivery for inhaled antibiotics are discussed.

Pharmacokinetics and pharmacodynamics of aerosolized antibacterial agents in chronically infected cystic fibrosis patients

Bacteria adapt to growth in lungs of patients with cystic fibrosis (CF) by selection of heterogeneously resistant variants that are not detected by conventional susceptibility testing but are selected for rapidly during antibacterial treatment. Therefore, total bacterial counts and antibiotic susceptibilities are misleading indicators of infection and are not helpful as guides for therapy decisions or efficacy endpoints. High drug concentrations delivered by aerosol may maximize efficacy, as decreased drug susceptibilities of the pathogens are compensated for by high target site concentrations. However, reductions of the bacterial load in sputum and improvements in lung function were within the same ranges following aerosolized and conventional therapies. Furthermore, the use of conventional pharmacokinetic/pharmacodynamic (PK/PD) surrogates correlating pharmacokinetics in serum with clinical cure and presumed or proven eradication of the pathogen as a basis for PK/PD investigations in CF patients is irrelevant, as minimization of systemic exposure is one of the main objectives of aerosolized therapy; in addition, bacterial pathogens cannot be eradicated, and chronic infection cannot be cured. Consequently, conventional PK/PD surrogates are not applicable to CF patients. It is nonetheless obvious that systemic exposure of patients, with all its sequelae, is minimized and that the burden of oral treatment for CF patients suffering from chronic infections is reduced.

Global fluoroquinolone resistance epidemiology and implictions for clinical use

This paper on the fluoroquinolone resistance epidemiology stratifies the data according to the different prescription patterns by either primary or tertiary caregivers and by indication. Global surveillance studies demonstrate that fluoroquinolone resistance rates increased in the past years in almost all bacterial species except S. pneumoniae and H. influenzae, causing community-acquired respiratory tract infections. However, 10 to 30% of these isolates harbored first-step mutations conferring low level fluoroquinolone resistance. Fluoroquinolone resistance increased in Enterobacteriaceae causing community acquired or healthcare associated urinary tract infections and intraabdominal infections, exceeding 50% in some parts of the world, particularly in Asia. One to two-thirds of Enterobacteriaceae producing extended spectrum β-lactamases were fluoroquinolone resistant too. Furthermore, fluoroquinolones select for methicillin resistance in Staphylococci. Neisseria gonorrhoeae acquired fluoroquinolone resistance rapidly; actual resistance rates are highly variable and can be as high as almost 100%, particularly in Asia, whereas resistance rates in Europe and North America range from <10% in rural areas to >30% in established sexual networks. In general, the continued increase in fluoroquinolone resistance affects patient management and necessitates changes in some guidelines, for example, treatment of urinary tract, intra-abdominal, skin and skin structure infections, and traveller's diarrhea, or even precludes the use in indications like sexually transmitted diseases and enteric fever.

Targeted Antibiotic Prophylaxis for Lung Transplantation in Cystic Fibrosis Patients Colonised with Pseudomonas aeruginosa Using Multiple Combination Bactericidal Testing

Early infection is a recognised complication after lung transplantation in patients with cystic fibrosis (CF). Our centre uses multiple combination bactericidal testing (MCBT) when determining appropriate peritransplant prophylactic regimens. To evaluate our strategy, we compared the incidence of posttransplant infection in patients whose peritransplant antimicrobial regimens were determined using MCBT versus standard sensitivity testing. Patients with CF who were infected with Pseudomonas aeruginosa and underwent lung transplantations between 2000 and 2010 were included. Data was collected from clinical records and our microbiology database. Microorganisms cultured were mapped against antibiotic resistance, method of sensitivity testing, and antibiotics administered peritransplant. 129 patients were identified (mean age 28, male : female, 63 : 66). Fifty patients (38.8%) had antibiotics determined by MCBT. Two patients in the MCBT group developed septicaemia, 13 in the conventional group (P ≤ 0.05, 2-tailed Fisher's test). Sepsis was attributable to P. aeruginosa in one patient from the MCBT group and seven patients in the conventional group (P = 0.15). P. aeruginosa was recovered from the posttransplant pleural fluid of one patient who received MCBT-guided prophylaxis, six patients in the conventional group (P = 0.25). Patients given antibiotics based on MCBT had significantly lower rates of septicaemia and lower rates of empyema.

Changes in cystic fibrosis sputum microbiology in the United States between 1995 and 2008

STUDY OBJECTIVES

The study objective was to identify changes in cystic fibrosis (CF) sputum microbiology over 13 years.

METHODS

This study recruited a contemporary cohort of CF patients meeting similar eligibility criteria as the 520 subjects in the Phase 3 trials of inhaled tobramycin (historical cohort). Subjects submitted a single sputum specimen to a centralized laboratory for culture and susceptibility testing. Data were summarized and cross-sectional prevalence estimates were compared between cohorts. Exploratory analyses examined associations between recent antibiotic exposures and resistance prevalence.

RESULTS

Sputum samples from 267 subjects from 33 US CF centers were submitted for testing. A total of 656 Pseudomonas aeruginosa isolates were identified from 253 culture-positive subjects. Comparison between cohorts revealed an increase in the prevalence of subjects with tobramycin resistant (11.8% vs. 30.4%, P < 0.001) and amikacin resistant (24.2% vs. 42.7%, P < 0.001) P. aeruginosa. Prevalence of ciprofloxacin resistance was similar (34.4% vs. 33.6%, P = 0.81). Within the contemporary cohort, potential associations between recent antibiotic exposures and prevalence of P. aeruginosa resistance were examined; findings included that exposure to intravenous carbapenems was significantly associated with aztreonam resistance, meropenem resistance, and multidrug resistance (P = 0.0002, P = 0.0003, and P = 0.0002, respectively). Prevalences of Staphylococcus aureus, methicillin-resistant S. aureus, Stenotrophomonas maltophilia, and Achromobacter xylosoxidans were also increased in the contemporary cohort.

CONCLUSIONS

We identified important changes in the patterns of CF airway microbiology, including increased aminoglycoside resistance and prevalence of other antibiotic resistant organisms. These changes are concerning to clinicians caring for individuals with CF because they impact treatment options. These data point to a critical need to develop new antimicrobials for CF.

Molecular analysis of diversity within the genus Pseudomonas in the lungs of cystic fibrosis patients

The genus Pseudomonas contains species that can act as human pathogens and are important in many infections such as those occurring in the lungs of many cystic fibrosis (CF) patients. Current methodologies that rely on the cultivation of bacteria are too cumbersome and often lack sufficient discriminatory power to define the diversity of Pseudomonas spp. As a result, molecular-based approaches have many advantages when attempting to differentiate between species of this genus. This study assessed the ability of terminal restriction fragment length polymorphism (T-RFLP) profiling of the 16S-23S rRNA ITS1 gene region to differentiate species of the genus Pseudomonas. Before application to clinical samples, this approach was validated on a panel of 10 different Pseudomonas spp. T-RFLP profiling of the 16S-23S rRNA ITS1 gene region amplified from these strains differentiated all Pseudomonas spp. tested. The presence of Pseudomonas spp. in CF sputum was assessed through the detection of this ITS1 gene region as amplified from DNA extracted from 40 samples of CF sputum. The ITS1 gene region was detected in 75% of these samples, including 5 from which no Pseudomonas spp. had been identified using culture-based methods. In silico analysis showed that all sequences amplified had a high homology with the ITS1 region of Pseudomonas aeruginosa. T-RFLP gave data that were consistent with the band being generated from P. aeruginosa for each patient. No correlation between Pseudomonas diversity and severity of lung disease was observed in this group of CF patients. This study has however shown that molecular analysis of the ITS1 region is effective in resolving diversity within the genus Pseudomonas. The wider use of this application is discussed.

Efflux unbalance in Pseudomonas aeruginosa isolates from cystic fibrosis patients

Retrospective analysis of 189 nonredundant strains of Pseudomonas aeruginosa sequentially recovered from the sputum samples of 46 cystic fibrosis (CF) patients over a 10-year period (1998 to 2007) revealed that 53 out of 189 (28%) samples were hypersusceptible to the beta-lactam antibiotic ticarcillin (MIC < or = 4 microg/ml) (phenotype dubbed Tic(hs)). As evidenced by trans-complementation and gene inactivation experiments, the mutational upregulation of the efflux system MexXY was responsible for various degrees of resistance to aminoglycosides in a selection of 11 genotypically distinct strains (gentamicin MICs from 2 to 64 microg/ml). By demonstrating for the first time that the MexXY pump may evolve in CF strains, we found that a mutation leading to an F1018L change in the resistance-nodulation-cell division (RND) transporter MexY was able to increase pump-promoted resistance to aminoglycosides, cefepime, and fluoroquinolones twofold. The inactivation of the mexB gene (which codes for the RND transporter MexB) in the 11 selected strains showed that the Tic(hs) phenotype was due to a mutational or functional loss of function of MexAB-OprM, the multidrug efflux system known to contribute to the natural resistance of P. aeruginosa to beta-lactams (e.g., ticarcillin and aztreonam), fluoroquinolones, tetracycline, and novobiocin. Two of the selected strains synthesized abnormally low amounts of the MexB protein, and 3 of 11 strains expressed truncated MexB (n = 2) or MexA (n = 1) polypeptide as a result of mutations in the corresponding genes, while 7 of 11 strains produced wild-type though nonfunctional MexAB-OprM pumps at levels similar to or even higher than that of reference strain PAO1. Overall, our data indicate that while MexXY is necessary for P. aeruginosa to adapt to the hostile environment of the CF lung, the MexAB-OprM pump is dispensable and tends to be lost or inactivated in subpopulations of P. aeruginosa.

[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.

Recent advances in the microbiology of respiratory tract infection in cystic fibrosis

INTRODUCTION

Infection is a major cause of morbidity and mortality in patients with cystic fibrosis (CF). Research on CF infection has highlighted differences from other respiratory infections--both in the range and the nature of the organisms--especially in chronic infection. This is a rapidly advancing field of microbiology and is bringing insights into the complexity and adaptations of bacteria causing chronic infection in the respiratory tract.

AREAS OF AGREEMENT AND CONTROVERSY

The epidemiology of some infections in CF has changed, with reduction in spread of Burkholderia cenocepacia following patient segregation. Conversely, epidemic strains of Pseudomonas aeruginosa have emerged, which spread between patients; previously, most P. aeruginosa strains were patient-specific. Studies on hypermutators, quorum sensing, biofilm growth and the development of molecular identification have shed light on pathogenicity, microbial adaptation to the host and complexity of infection in CF. Non-tuberculous mycobacteria are emerging pathogens in CF; however, there is much to learn about pathogenicity and treatment of these infections. Species of aerobic and anaerobic bacteria, more commonly encountered in the upper tract, are found in significant numbers in CF sputum. The significance of this is however under debate. Finally, although the clinical relevance of conventional antibiotic susceptibility testing for chronic CF pathogens has been questioned, there are no clear alternatives.

EMERGING AREAS FOR DEVELOPING RESEARCH

Much has been learnt about pathogenicity, evolution of CF pathogens and development of antibiotic resistance. The need is to focus on clinical relevance of these observations to improve diagnosis, prevention and treatment of CF infection.