Effect of L-arginine on cystic fibrosis Pseudomonas aeruginosa biofilms.

Cystic fibrosis (CF) airways are L-arginine deficient which may affect susceptibility to infection with certain pathogens. The potential impact of L-arginine supplementation on Pseudomonas aeruginosa, a common CF airway pathogen, is unclear. This study investigated the effects of L-arginine on P. aeruginosa biofilm cultures, using the laboratory strain PAO1 and multi-drug resistant CF clinical isolates. P. aeruginosa biofilms were grown in a chambered cover-glass slide model for 24 h, then exposed to either L-arginine alone or combined with tobramycin for an additional 24 h. Biofilms were visualized using confocal microscopy, and viable cells were measured via plating for colony-forming units. Increasing concentrations of L-arginine in bacterial culture medium reduced the biovolume of P. aeruginosa in a dose-dependent manner. Notably, L-arginine concentrations within the physiological range (50 mM and 100 mM) in combination with tobramycin promoted biofilm growth, while higher concentrations (600 mM and 1200 mM) inhibited growth. These findings demonstrate the potential of L-arginine as an adjuvant therapy to inhaled tobramycin in treating P. aeruginosa infections in people with CF.

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.

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.

A Prolonged Outbreak of Human Adenovirus A31 (HAdV-A31) Infection on a Pediatric Hematopoietic Stem Cell Transplantation Ward with Whole Genome Sequencing Evidence of International Linkages.

A surge in hematopoietic stem cell transplantation (HSCT) human adenovirus A31 (HAdV-A31) infections was initially observed in late 2014/2015 at SickKids (SK) Hospital, Toronto, Canada. In response, enhanced laboratory monitoring for all adenovirus infections was conducted. Positive samples underwent genotyping, viral culture, and, in selected cases, whole-genome sequencing (WGS). HAdV-A31 specimens/DNA obtained from four international pediatric HSCT centers also underwent WGS. During the SK outbreak period (27 October 2014 to 31 October 2018), 17/20 HAdV-A31 isolates formed a distinct clade with 0 to 8 mutations between the closest neighbors. Surveillance before and after the outbreak detected six additional HAdV-A31 HSCT cases; three of the four sequenced cases clustered within the outbreak clade. Two SK outbreak isolates were identical to sequences from two patients in an outbreak in England. Three SK non-outbreak sequences also had high sequence similarity to strains from three international centers. Environmental PCR testing of the HSCT ward showed significant adenovirus contamination. Despite intense infection control efforts, we observed re-occurrence of infection with the outbreak strain. Severe but nonfatal infection was observed more commonly with HAdV-A31 compared to other genotypes, except HAdV-C1. Our findings strongly implicate nosocomial spread of HAdV-A31 over 10 years on a HSCT unit and demonstrate the value of WGS in defining and mapping the outbreak. Close linkages among strains in different countries suggest international dissemination, though the mechanism is undetermined. This large, extended outbreak emphasizes the pre-eminent role of HAdV-A31 in causing intractable pediatric HSCT outbreaks of severe illness worldwide.

Assessment of panfungal PCR performance with formalin-fixed paraffin-embedded tissue specimens†.

We reviewed the performance of a panfungal ITS-2 PCR and Sanger sequencing assay performed on 88 FFPE specimens at The Hospital for Sick Children (Toronto, Canada) in 2019. A potential fungal pathogen was identified by ITS PCR in 62.7 and 2.9% of positive and negative direct slide examination of tissue specimens, respectively. ITS amplicons were detected in 87/88 specimens, with 53/88 (60.2%) considered as 'positive-contaminants' and 34/88 (38.6%) as 'positive-potential pathogen' upon sequencing. Potential pathogens included Blastomyces dermatitidis (17.1%), Cryptococcus neoformans (17.1%), Histoplasma capsulatum (14.3%) and Mucormycetes (11.4%). Laboratories should only perform ITS PCR on FFPE tissues if fungal elements have been confirmed on histopathology slides. LAY SUMMARY: In this study, we examined how well a DNA-based test could detect DNA from fungi in archived human biopsy tissues. The best performance was achieved if fungi were seen in the tissue under a microscope before being tested. Our results indicate that we should only use this test if these conditions are met.

Evaluation of digital dispense-assisted broth microdilution antimicrobial susceptibility testing for Pseudomonas aeruginosa isolates.

Antimicrobial susceptibility testing (AST) is essential for detecting resistance in Pseudomonas aeruginosa and other bacterial pathogens. Here we evaluated the performance of broth microdilution (BMD) panels created using a semi-automated liquid handler, the D300e Digital Dispenser (Tecan Group Ltd., CH) that relies on inkjet printing technology. Microtitre panels (96-well) containing nine twofold dilutions of 12 antimicrobials from five classes (ß-lactams, ß-lactam/ß-lactamase inhibitors, aminoglycosides, fluoroquinolones, polymyxins) were prepared in parallel using the D300e Digital Dispenser and standard methods described by CLSI/ISO. To assess performance, panels were challenged with three well characterized quality control organisms and 100 clinical P. aeruginosa isolates. Traditional agreement and error measures were used for evaluation. Essential (EA) and categorical (CA) agreements were 92.7% and 98.0% respectively for P. aeruginosa isolates with evaluable on-scale results. The majority of minor errors that fell outside acceptable EA parameters (≥ ± 1 dilution, 1.9%) were seen with aztreonam (5%) and ceftazidime (4%), however all antimicrobials displayed acceptable performance in this situation. Differences in MIC were often log2 dilution lower for D300e dispensed panels. Major and very major errors were noted for aztreonam (2.6%) and cefepime (1.7%) respectively. The variable performance of D300e panels suggests that further testing is required to confirm their diagnostic utility for P. aeruginosa.

Quantifying the Effects of Antimicrobials on In vitro Biofilm Architecture using COMSTAT Software.

Biofilms are aggregates of microorganisms that rely on a self-produced matrix of extracellular polymeric substance for protection and structural integrity. The nosocomial pathogen, Pseudomonas aeruginosa, is known to adopt a biofilm mode of growth, causing chronic pulmonary infection in patients with cystic fibrosis (CF). The computer program, COMSTAT, is a useful tool for quantifying antimicrobial-induced changes in P. aeruginosa biofilm architecture by extracting data from three-dimensional confocal images. However, standardized operation of the software is less commonly addressed, which is important for optimal reporting of biofilm behavior and cross-center comparison. Thus, the aim of this protocol is to provide a simple and reproducible framework for quantifying in vitro biofilm structures under varying antimicrobial conditions via COMSTAT. The technique is modeled using a CF P. aeruginosa isolate, grown in the form of biofilm replicates, and exposed to tobramycin and the anti-Psl monoclonal antibody, Psl0096. The step-by-step approach aims to reduce user ambiguity and minimize the chance of overlooking crucial image-processing steps. Specifically, the protocol emphasizes the elimination of subjective variations associated with the manual operation of COMSTAT, including image segmentation and the selection of appropriate quantitative analysis functions. Although this method requires users to spend additional time processing confocal images prior to running COMSTAT, it helps minimize misrepresented biofilm heterogenicity in automated outputs.

Ecological Succession of Polymicrobial Communities in the Cystic Fibrosis Airways.

Antimicrobial therapies against cystic fibrosis (CF) lung infections are largely aimed at the traditional, well-studied CF pathogens such as Pseudomonas aeruginosa and Burkholderia cepacia complex, despite the fact that the CF lung harbors a complex and dynamic polymicrobial community. A clinical focus on the dominant pathogens ignores potentially important community-level interactions in disease pathology, perhaps explaining why these treatments are often less effective than predicted based on in vitro testing. A better understanding of the ecological dynamics of this ecosystem may enable clinicians to harness these interactions and thereby improve treatment outcomes. Like all ecosystems, the CF lung microbial community develops through a series of stages, each of which may present with distinct microbial communities that generate unique host-microbe and microbe-microbe interactions, metabolic profiles, and clinical phenotypes. While insightful models have been developed to explain some of these stages and interactions, there is no unifying model to describe how these infections develop and persist. Here, we review current perspectives on the ecology of the CF airway and present the CF Ecological Succession (CFES) model that aims to capture the spatial and temporal complexity of CF lung infection, address current challenges in disease management, and inform the development of ecologically driven therapeutic strategies.

Visualization of Pseudomonas aeruginosa within the Sputum of Cystic Fibrosis Patients.

Early detection and eradication of Pseudomonas aeruginosa within the lungs of cystic fibrosis patients can reduce the chance of developing chronic infection. The development of chronic P. aeruginosa infections is associated with a decline in lung function and increased morbidity. Therefore, there is a great interest in elucidating the reasons for the failure to eradicate P. aeruginosa with antibiotic therapy which occurs in approximately 10-40% of pediatric patients. One of many factors that can affect host clearance of P. aeruginosa and antibiotic susceptibility is variations in spatial organization (such as aggregation or biofilm formation) and polysaccharide production. Therefore, we were interested in visualizing the in situ characteristics of P. aeruginosa within the sputum of CF patients. A tissue clearing technique was applied to sputum samples after embedding the samples into a hydrogel matrix to retain the 3D structures relative to host cells. After tissue clearing, fluorescent labels and dyes were added to allow visualization. Fluorescence in situ hybridization was performed for the visualization of bacterial cells, binding of fluorescently labeled anti-Psl-antibodies for the visualization of the exopolysaccharide and DAPI staining to stain host cells to obtain structural insight. These methods allowed for the high-resolution imaging of P. aeruginosa within the sputum of CF patients via confocal laser scanning microscopy.

Clinical Outcomes Associated with Burkholderia cepacia Complex Infection in Patients with Cystic Fibrosis.

Rationale: Little is known in contemporary cystic fibrosis (CF) cohorts about the outcomes after new Burkholderia species infections.Objectives: To evaluate the changing epidemiology and clinical outcomes associated with Burkholderia species infections in persons with CF.Methods: A cohort study of children and adults with CF was conducted from 1997 to 2018 in Toronto, Canada. Patients were characterized as those with no history of Burkholderia species infection and as those who were culture-positive for Burkholderia species for the first time in this time frame and were categorized by species (B. gladioli, B. cenocepacia, B. multivorans, or other) and strain (B. cenocepacia ET-12). Cox models were used to estimate the risk of death or transplantation. Mixed-effects models were used to assess the impact of Burkholderia species on odds of pulmonary exacerbations and effect on lung function (percentage predicted forced expiratory volume in 1 second [FEV1]).Results: A total of 1,196 patients were followed over 20 years; 88 patients (7.4%) had one or more culture-positive for Burkholderia species. Patients with ET-12 infection had a median time to death of 1.95 years compared with 5.30-6.72 years for those with other Burkholderia infections. ET-12 infection was associated with a greater risk of death or transplantation compared with patients with no history of Burkholderia infection in a univariate model (hazard ratio, 3.92; 95% confidence interval 2.25-6.81) but was no longer significant after adjusting for confounders. Pulmonary exacerbations were more common in those with Burkholderia infections and remained significant in the ET-12 group after adjusting for confounders (odds ratio, 2.96; 95% confidence interval, 1.17-7.53). No differences were noted in baseline FEV1% or the rate of FEV1% decline between the groups with and without Burkholderia species infection.Conclusions: With the exception of ET-12, the acquisition of Burkholderia species infection did not appear to worsen clinical outcomes compared with those with no history of infection. Given this, prognosis, management and clinical trial inclusion protocols may need to be reevaluated for persons with Burkholderia infection.

Microbiome networks and change-point analysis reveal key community changes associated with cystic fibrosis pulmonary exacerbations.

Over 90% of cystic fibrosis (CF) patients die due to chronic lung infections leading to respiratory failure. The decline in CF lung function is greatly accelerated by intermittent and progressively severe acute pulmonary exacerbations (PEs). Despite their clinical impact, surprisingly few microbiological signals associated with PEs have been identified. Here we introduce an unsupervised, systems-oriented approach to identify key members of the microbiota. We used two CF sputum microbiome data sets that were longitudinally collected through periods spanning baseline health and PEs. Key taxa were defined based on three strategies: overall relative abundance, prevalence, and co-occurrence network interconnectedness. We measured the association between changes in the abundance of the key taxa and changes in patient clinical status over time via change-point detection, and found that taxa with the highest level of network interconnectedness tracked changes in patient health significantly better than taxa with the highest abundance or prevalence. We also cross-sectionally stratified all samples into the clinical states and identified key taxa associated with each state. We found that network interconnectedness most strongly delineated the taxa among clinical states, and that anaerobic bacteria were over-represented during PEs. Many of these anaerobes are oropharyngeal bacteria that have been previously isolated from the respiratory tract, and/or have been studied for their role in CF. The observed shift in community structure, and the association of anaerobic taxa and PEs lends further support to the growing consensus that anoxic conditions and the subsequent growth of anaerobic microbes are important predictors of PEs.

Penicillin-binding protein 3 is a common adaptive target among Pseudomonas aeruginosa isolates from adult cystic fibrosis patients treated with ß-lactams.

OBJECTIVE: Determining the mechanisms that modulate ß-lactam resistance in clinical Pseudomonas aeruginosa (P. aeruginosa) isolates can be challenging, as the molecular profiles identified in mutation-based or expression-based resistance determinant screens may not correlate with in vitro phenotypes. One of the lesser studied resistance mechanisms in P. aeruginosa is the modification of penicillin-binding protein 3 (pbpB/ftsI). This study reported that nonsynonymous polymorphisms within pbpB frequently occur among ß-lactam resistant sputum isolates, and are associated with unique antibiotic susceptibility patterns. METHODS: Longitudinally collected isolates (n = 126) from cystic fibrosis (CF) patients with or without recent ß-lactam therapy or of non-clinical origin were tested for susceptibility to six ß-lactams (aztreonam, ceftazidime, cefsulodin, cefepime, meropenem, and piperacillin). Known ß-lactam resistance mechanisms were characterised by polymerase chain reaction (PCR)-based methods, and polymorphisms in the transpeptidase-encoding domain of pbpB identified by sequencing. RESULTS: Twelve nonsynonymous polymorphisms were detected among 86 isolates (67%) from five CF patients with a history of ß-lactam therapy, compared with one polymorphism in 30 (3.3%) from three patients who had not received ß-lactam treatments. No nonsynonymous polymorphisms were found in ten environmental isolates. Multiple pbpB alleles, often with different combinations of polymorphisms, were detected within the population of strains from each CF patient for up to 2.6 years. Traditional patterns of ampC or mexA de-repression reduced expression of oprD or the presence of extended-spectrum ß-lactamases were not observed in resistant isolates with nonsynonymous polymorphisms in pbpB. CONCLUSION: This study's findings suggest that pbpB is a common adaptive target, and may contribute to the development of ß-lactam resistance in P. aeruginosa.

Burkholderia multivorans septicemia in a pediatric liver transplant patient.

"Cepacia syndrome", caused by Burkholderia cepacia complex and often associated with cystic fibrosis, carries a high mortality rate. It is rare for Burkholderia multivorans, a species within the B. cepacia complex, to cause cepacia syndrome even among patients with cystic fibrosis. This is the first reported fatal case of cepacia syndrome caused by B. multivorans occurring in a pediatric liver transplant recipient who does not have cystic fibrosis. We describe the unique characteristics of this pathogen among the non-cystic fibrosis population and the importance of early recognition and treatment.

A genome-wide association analysis reveals a potential role for recombination in the evolution of antimicrobial resistance in Burkholderia multivorans.

Cystic fibrosis (CF) lung infections caused by members of the Burkholderia cepacia complex, such as Burkholderia multivorans, are associated with high rates of mortality and morbidity. We performed a population genomics study of 111 B. multivorans sputum isolates from one CF patient through three stages of infection including an early incident isolate, deep sampling of a one-year period of chronic infection occurring weeks before a lung transplant, and deep sampling of a post-transplant infection. We reconstructed the evolutionary history of the population and used a lineage-controlled genome-wide association study (GWAS) approach to identify genetic variants associated with antibiotic resistance. We found the incident isolate was basally related to the rest of the strains and more susceptible to antibiotics from three classes (ß-lactams, aminoglycosides, quinolones). The chronic infection isolates diversified into multiple, distinct genetic lineages and showed reduced antimicrobial susceptibility to the same antibiotics. The post-transplant reinfection isolates derived from the same source as the incident isolate and were genetically distinct from the chronic isolates. They also had a level of susceptibility in between that of the incident and chronic isolates. We identified numerous examples of potential parallel pathoadaptation, in which multiple mutations were found in the same locus or even codon. The set of parallel pathoadaptive loci was enriched for functions associated with virulence and resistance. Our GWAS analysis identified statistical associations between a polymorphism in the ampD locus with resistance to ß-lactams, and polymorphisms in an araC transcriptional regulator and an outer membrane porin with resistance to both aminoglycosides and quinolones. Additionally, these three loci were independently mutated four, three and two times, respectively, providing further support for parallel pathoadaptation. Finally, we identified a minimum of 14 recombination events, and observed that loci carrying putative parallel pathoadaptations and polymorphisms statistically associated with ß-lactam resistance were over-represented in these recombinogenic regions.

Epidemiology of Clonal Pseudomonas aeruginosa Infection in a Canadian Cystic Fibrosis Population.

RATIONALE: The extent of the genetic relatedness among Pseudomonas aeruginosa isolates and its impact on clinical outcomes in the cystic fibrosis (CF) population is poorly understood. OBJECTIVES: The objectives of this study were to determine the prevalence of clonal P. aeruginosa infection in Canada and to associate P. aeruginosa genotypes with clinical outcomes. METHODS: This was an observational study of adult and pediatric patients with CF across Canada. Isolates were typed using multilocus sequence typing. A clone was defined as sharing at least six of seven alleles. Genotyping results were associated with clinical outcomes, including forced expiratory volume in 1 second, body mass index, rate of pulmonary exacerbation, and death/transplant. RESULTS: A total of 1,537 P. aeruginosa isolates were genotyped to 403 unique sequence types (STs) in 402 individuals with CF. Although 39% of STs were shared, most were shared only among a small number of subjects, and the majority (79%) of the genetic diversity in P. aeruginosa isolates was observed between patients. There were no significant differences in clinical outcomes according to genotype. However, patients with a dynamic, changing ST infection pattern had both a steeper decline in forced expiratory volume in 1 second (-2.9% predicted change/yr, 95% confidence interval [CI] = -3.8 to -1.9 compared with 0.4, 95% CI = -0.3 to 1.0; P < 0.001) and body mass index (-1.0 percentile change/yr, 95% CI = -1.6 to -0.3 compared with -0.1, 95% CI = -0.7 to 0.5; P = 0.047) than those with a stable infection with the same ST. CONCLUSIONS: There was no widespread sharing of dominant clones in our CF population, and the majority of the genetic diversity in P. aeruginosa was observed between patients. Changing genotypes over time within an individual was associated with worse clinical outcomes.

MexXY efflux pump overexpression and aminoglycoside resistance in cystic fibrosis isolates of Pseudomonas aeruginosa from chronic infections.

In this study, we analyzed 15 multidrug-resistant cystic fibrosis isolates of Pseudomonas aeruginosa from chronic lung infections for expression of 4 different multidrug efflux systems (MexAB-OprM, MexCD-OprJ, MexEF-OprN, and MexXY), using quantitative reverse transcriptase PCR. Overexpression of MexXY pump was observed in all of the isolates tested. Analysis of regulatory genes that control the expression of these 4 efflux pumps revealed a number of previously uncharacterized mutations. Our work shows that MexXY pump overexpression is common in cystic fibrosis isolates and could be contributing to their reduced aminoglycoside susceptibility. Further, we also identified novel mutations in the regulatory genes of the 4 abovementioned Resistance-Nodulation-Division superfamily pumps that may be involved in the overexpression of these pumps.

Navigating social and ethical challenges of biobanking for human microbiome research.

BACKGROUND: Biobanks are considered to be key infrastructures for research development and have generated a lot of debate about their ethical, legal and social implications (ELSI). While the focus has been on human genomic research, rapid advances in human microbiome research further complicate the debate. DISCUSSION: We draw on two cystic fibrosis biobanks in Toronto, Canada, to illustrate our points. The biobanks have been established to facilitate sample and data sharing for research into the link between disease progression and microbial dynamics in the lungs of pediatric and adult patients. We begin by providing an overview of some of the ELSI associated with human microbiome research, particularly on the implications for the broader society. We then discuss ethical considerations regarding the identifiability of samples biobanked for human microbiome research, and examine the issue of return of results and incidental findings. We argue that, for the purposes of research ethics oversight, human microbiome research samples should be treated with the same privacy considerations as human tissues samples. We also suggest that returning individual microbiome-related findings could provide a powerful clinical tool for care management, but highlight the need for a more grounded understanding of contextual factors that may be unique to human microbiome research. CONCLUSIONS: We revisit the ELSI of biobanking and consider the impact that human microbiome research might have. Our discussion focuses on identifiability of human microbiome research samples, and return of research results and incidental findings for clinical management.

Early-Onset Invasive Candidiasis in Extremely Low Birth Weight Infants: Perinatal Acquisition Predicts Poor Outcome.

BACKGROUND: Neonatal invasive candidiasis (IC) presenting in the first week of life is less common and less well described than later-onset IC. Risk factors, clinical features, and disease outcomes have not been studied in early-onset disease (EOD, ≤7 days) or compared to late-onset disease (LOD, >7 days). METHODS: All extremely low birth weight (ELBW, <1000 g) cases with IC and controls from a multicenter study of neonatal candidiasis enrolled from 2001 to 2003 were included in this study. Factors associated with occurrence and outcome of EOD in ELBW infants were determined. RESULTS: Forty-five ELBW infants and their 84 matched controls were included. Fourteen (31%) ELBW infants had EOD. Birth weight <750 g, gestation <25 weeks, chorioamnionitis, and vaginal delivery were all strongly associated with EOD. Infection with Candida albicans, disseminated disease, pneumonia, and cardiovascular disease were significantly more common in EOD than in LOD. The EOD case fatality rate (71%) was higher than in LOD (32%) or controls (15%) (P = .0001). The rate of neurodevelopmental impairment and mortality combined was similar in EOD (86%) and LOD (72%), but higher than in controls (32%; P = .007). CONCLUSIONS: ELBW infants with EOD have a very poor prognosis compared to those with LOD. The role of perinatal transmission in EOD is supported by its association with chorioamnionitis, vaginal delivery, and pneumonia. Dissemination and cardiovascular involvement are common, and affected infants often die. Empiric treatment should be considered for ELBW infants delivered vaginally who have pneumonia and whose mothers have chorioamnionitis or an intrauterine foreign body.

Effect of High-Dose Antimicrobials on Biofilm Growth of Achromobacter Species Isolated from Cystic Fibrosis Patients.

MICs and biofilm inhibitory concentrations (BICs) were measured for 68 cystic fibrosis (CF) Achromobacter isolates for amikacin, aztreonam, colistin, levofloxacin, and tobramycin. With the exception of colistin and levofloxacin, the remaining antibiotics had MIC90s, BICs at which 50% of the isolates were susceptible (BIC50s), and BICs at which 90% of the isolates were susceptible (BIC90s) equal to or above the highest concentrations tested. In a biofilm model, tobramycin was able to significantly increase killing of bacterial cells compared to controls, for intermediate-resistant strains only, at concentrations of 1,000 and 2,000 µg/ml.

Activity of Tobramycin against Cystic Fibrosis Isolates of Burkholderia cepacia Complex Grown as Biofilms.

Pulmonary infection with Burkholderia cepacia complex in cystic fibrosis (CF) patients is associated with more-rapid lung function decline and earlier death than in CF patients without this infection. In this study, we used confocal microscopy to visualize the effects of various concentrations of tobramycin, achievable with systemic and aerosolized drug administration, on mature B. cepacia complex biofilms, both in the presence and absence of CF sputum. After 24 h of growth, biofilm thickness was significantly reduced by exposure to 2,000 µg/ml of tobramycin for Burkholderia cepacia, Burkholderia multivorans, and Burkholderia vietnamiensis; 200 µg/ml of tobramycin was sufficient to reduce the thickness of Burkholderia dolosa biofilm. With a more mature 48-h biofilm, significant reductions in thickness were seen with tobramycin at concentrations of ≥100 µg/ml for all Burkholderia species. In addition, an increased ratio of dead to live cells was observed in comparison to control with tobramycin concentrations of ≥200 µg/ml for B. cepacia and B. dolosa (24 h) and ≥100 µg/ml for Burkholderia cenocepacia and B. dolosa (48 h). Although sputum significantly increased biofilm thickness, tobramycin concentrations of 1,000 µg/ml were still able to significantly reduce biofilm thickness of all B. cepacia complex species with the exception of B. vietnamiensis. In the presence of sputum, 1,000 µg/ml of tobramycin significantly increased the dead-to-live ratio only for B. multivorans compared to control. In summary, although killing is attenuated, high-dose tobramycin can effectively decrease the thickness of B. cepacia complex biofilms, even in the presence of sputum, suggesting a possible role as a suppressive therapy in CF.