Microbiology of airway disease in patients with cystic fibrosis

The changing epidemiology of pulmonary infection in children and adolescents with cystic fibrosis: an 18-year experience

The impact of evolving treatment regimens, airway clearance strategies, and antibiotic combinations on the incidence and prevalence of respiratory infection in cystic fibrosis (CF) in children and adolescents remains unclear. The incidence, prevalence, and prescription trends from 2002 to 2019 with 18,339 airway samples were analysed. Staphylococcus aureus [- 3.86% (95% CI - 5.28-2.43)] showed the largest annual decline in incidence, followed by Haemophilus influenzae [- 3.46% (95% CI - 4.95-1.96)] and Pseudomonas aeruginosa [- 2.80%95% CI (- 4.26-1.34)]. Non-tuberculous mycobacteria and Burkholderia cepacia showed a non-significant increase in incidence. A similar pattern of change in prevalence was observed. No change in trend was observed in infants < 2 years of age. The mean age of the first isolation of S. aureus (p < 0.001), P. aeruginosa (p < 0.001), H. influenza (p < 0.001), Serratia marcescens (p = 0.006) and Aspergillus fumigatus (p = 0.02) have increased. Nebulised amikacin (+ 3.09 ± 2.24 prescription/year, p = 0.003) and colistin (+ 1.95 ± 0.3 prescriptions/year, p = 0.032) were increasingly prescribed, while tobramycin (- 8.46 ± 4.7 prescriptions/year, p < 0.001) showed a decrease in prescription. Dornase alfa and hypertonic saline nebulisation prescription increased by 16.74 ± 4.1 prescriptions/year and 24 ± 4.6 prescriptions/year (p < 0.001). There is a shift in CF among respiratory pathogens and prescriptions which reflects the evolution of cystic fibrosis treatment strategies over time.

The role of human extracellular matrix proteins in defining Staphylococcus aureus biofilm infections

Twenty to forty one percent of the world's population is either transiently or permanently colonized by the Gram-positive bacterium, Staphylococcus aureus. In 2017, the CDC designated methicillin-resistant S. aureus (MRSA) as a serious threat, reporting ∼300 000 cases of MRSA-associated hospitalizations annually, resulting in over 19 000 deaths, surpassing that of HIV in the USA. S. aureus is a proficient biofilm-forming organism that rapidly acquires resistance to antibiotics, most commonly methicillin (MRSA). This review focuses on a large group of (>30) S. aureus adhesins, either surface-associated or secreted that are designed to specifically bind to 15 or more of the proteins that form key components of the human extracellular matrix (hECM). Importantly, this includes hECM proteins that are pivotal to the homeostasis of almost every tissue environment [collagen (skin), proteoglycans (lung), hemoglobin (blood), elastin, laminin, fibrinogen, fibronectin, and fibrin (multiple organs)]. These adhesins offer S. aureus the potential to establish an infection in every sterile tissue niche. These infections often endure repeated immune onslaught, developing into chronic, biofilm-associated conditions that are tolerant to ∼1000 times the clinically prescribed dose of antibiotics. Depending on the infection and the immune response, this allows S. aureus to seamlessly transition from colonizer to pathogen by subtly manipulating the host against itself while providing the time and stealth that it requires to establish and persist as a biofilm. This is a comprehensive discussion of the interaction between S. aureus biofilms and the hECM. We provide particular focus on the role of these interactions in pathogenesis and, consequently, the clinical implications for the prevention and treatment of S. aureus biofilm infections.

Two Different Isocitrate Dehydrogenases from Pseudomonas aeruginosa: Enzymology and Coenzyme-Evolutionary Implications

Pseudomonas aeruginosa PAO1, as an experimental model for Gram-negative bacteria, harbors two NADP+-dependent isocitrate dehydrogenases (NADP-IDHs) that were evolved from its ancient counterpart NAD-IDHs. For a better understanding of PaIDH1 and PaIDH2, we cloned the genes, overexpressed them in Escherichia coli and purified them to homogeneity. PaIDH1 displayed higher affinity to NADP+ and isocitrate, with lower Km values when compared to PaIDH2. Moreover, PaIDH1 possessed higher temperature tolerance (50 °C) and wider pH range tolerance (7.2-8.5) and could be phosphorylated. After treatment with the bifunctional PaIDH kinase/phosphatase (PaIDH K/P), PaIDH1 lost 80% of its enzymatic activity in one hour due to the phosphorylation of Ser115. Small-molecule compounds like glyoxylic acid and oxaloacetate can effectively inhibit the activity of PaIDHs. The mutant PaIDH1-D346I347A353K393 exhibited enhanced affinity for NAD+ while it lost activity towards NADP+, and the Km value (7770.67 μM) of the mutant PaIDH2-L589 I600 for NADP+ was higher than that observed for NAD+ (5824.33 μM), indicating a shift in coenzyme specificity from NADP+ to NAD+ for both PaIDHs. The experiments demonstrated that the mutation did not alter the oligomeric state of either protein. This study provides a foundation for the elucidation of the evolution and function of two NADP-IDHs in the pathogenic bacterium P. aeruginosa.

Virtual Screening of Potential RoxS Inhibitors and Evaluation of Their Antimicrobial Activity in Combination with Antibiotics against Clinically Resistant Bacteria

Pseudomonas aeruginosa with difficult-to-treat resistance has been designated as an urgent or serious threat by the CDC in the United States; therefore, novel antibacterial drugs and combination strategies are urgently needed. The sensor kinase RoxS is necessary for the aerobic growth of Pseudomonas aeruginosa. This study aimed to screen candidate RoxS inhibitors and evaluate their efficacy in treating multi-drug-resistant and extensively drug-resistant Pseudomonas aeruginosa in combination with meropenem and amikacin to identify promising combination strategies. RoxS protein structures were constructed using homology modeling and potential RoxS inhibitors, including Ezetimibe, Deferasirox, and Posaconazole, were screened from the FDA-approved ZINC drug database using molecular docking and molecular dynamics simulations. MIC and checkerboard assays were used to determine the in vitro antimicrobial efficacy of the three drugs in combination with antibiotics. The results of in vitro experiments showed an additive effect of 100 μg/mL Deferasirox or 16 μg/mL Posaconazole in combination with meropenem and a synergistic effect of 1.5 μg/mL Deferasirox and amikacin. In summary, these three drugs are potential inhibitors of RoxS, and their combination with meropenem or amikacin is expected to reverse the resistance of P. aeruginosa, providing new combination strategies for the treatment of clinically difficult-to-treat Pseudomonas aeruginosa.

Staphylococcus aureus Small-Colony Variants from Airways of Adult Cystic Fibrosis Patients as Precursors of Adaptive Antibiotic-Resistant Mutations

Prototypic Staphylococcus aureus and their small-colony variants (SCVs) are predominant in cystic fibrosis (CF), but the interdependence of these phenotypes is poorly understood. We characterized S. aureus isolates from adult CF patients over several years. Of 18 S. aureus-positive patients (58%), 13 (72%) were positive for SCVs. Characterization included genotyping, SCCmec types, auxotrophy, biofilm production, antibiotic susceptibilities and tolerance, and resistance acquisition rates. Whole-genome sequencing revealed that several patients were colonized with prototypical and SCV-related clones. Some clonal pairs showed acquisition of aminoglycoside resistance that was not explained by aminoglycoside-modifying enzymes, suggesting a mutation-based process. The characteristics of SCVs that could play a role in resistance acquisition were thus investigated further. For instance, SCV isolates produced more biofilm (p < 0.05) and showed a higher survival rate upon exposure to ciprofloxacin and vancomycin compared to their prototypic associated clones. SCVs also developed spontaneous rifampicin resistance mutations at a higher frequency. Accordingly, a laboratory-derived SCV (ΔhemB) acquired resistance to ciprofloxacin and gentamicin faster than its parent counterpart after serial passages in the presence of sub-inhibitory concentrations of antibiotics. These results suggest a role for SCVs in the establishment of persistent antibiotic-resistant clones in adult CF patients.

Epidemiological and Genetic Characteristics of Clinical Carbapenem-Resistant Pseudomonas aeruginosa Strains in Guangdong Province, China

Carbapenem-resistant Pseudomonas aeruginosa (CRPA) is a bacterial pathogen that may cause serious drug-resistant infections that are potentially fatal. To investigate the genetic characteristics of these organisms, we tested 416 P. aeruginosa strains recovered from 12 types of clinical samples collected in 29 different hospital wards in 10 hospitals in Guangdong Province, China, from 2017 to 2020. These strains were found to belong to 149 known sequence types (STs) and 72 novel STs, indicating that transmission of these strains involved multiple routes. A high rate of resistance to imipenem (89.4%) and meropenem (79.4%) and a high prevalence of pathogenic serotypes (76.4%) were observed among these strains. Six STs of global high-risk clones (HiRiCs) and a novel HiRiC strains, ST1971, which exhibited extensive drug resistance, were identified. Importantly, ST1971 HiRiC, which was unique in China, also exhibited high virulence, which alarmed the further surveillance on this highly virulent and highly resistant clone. Inactivation of the oprD gene and overexpression of efflux systems were found to be mainly responsible for carbapenem resistance in these strains; carriage of metallo-β-lactamase (MBL)-encoding genes was less common. Interestingly, frameshift mutations (49.0%) and introduction of a stop codon (22.4%) into the oprD genes were the major mechanisms of imipenem resistance. On the other hand, expression of the MexAB-OprM efflux pump and MBL-encoding genes were mechanisms of resistance in >70% of meropenem-resistant strains. The findings presented here provide insights into the development of effective strategies for control of worldwide dissemination of CRPA. IMPORTANCE Carbapenem-resistant Pseudomonas aeruginosa (CRPA) is a major concern in clinical settings worldwide, yet few genetic and epidemiological studies on CRPA strains have been performed in China. Here, we sequence and analyze the genomes of 416 P. aeruginosa strains from hospitals in China to elucidate the genetic, phenotypic, and transmission characteristics of CRPA strains and to identify the molecular signatures responsible for the observed increase in the prevalence of CRPA infections in China. These findings may provide new insight into the development of effective strategies for worldwide control of CRPA and minimize the occurrence of untreatable infections in clinical settings.

Current and Emerging Inhaled Antibiotics for Chronic Pulmonary Pseudomonas aeruginosa and Staphylococcus aureus Infections in Cystic Fibrosis

Characterized by impaired mucus transport and subsequent enhanced colonization of bacteria, pulmonary infection causes major morbidity and mortality in patients with cystic fibrosis (CF). Pseudomonas aeruginosa (P. aeruginosa) and Staphylococcus aureus (S. aureus) are the two most common types of bacteria detected in CF lungs, which undergo multiple adaptational mechanisms such as biofilm formation resulting in chronic pulmonary infections. With the advantages of greater airway concentration and minimized systemic toxicity, inhaled antibiotics are introduced to treat chronic pulmonary infection in CF. Inhaled tobramycin, aztreonam, levofloxacin, and colistin are the four most common discussed inhaled antibiotics targeting P. aeruginosa. Additionally, inhaled liposomal amikacin and murepavadin are also in development. This review will discuss the virulence factors and adaptational mechanisms of P. aeruginosa and S. aureus in CF. The mechanism of action, efficacy and safety, current status, and indications of corresponding inhaled antibiotics will be summarized. Combination therapy and the strategies to select an optimal inhaled antibiotic protocol will also be discussed.

In Vivo Role of Two-Component Regulatory Systems in Models of Urinary Tract Infections

Two-component signaling systems (TCSs) are finely regulated mechanisms by which bacteria adapt to environmental conditions by modifying the expression of target genes. In bacterial pathogenesis, TCSs play important roles in modulating adhesion to mucosal surfaces, resistance to antibiotics, and metabolic adaptation. In the context of urinary tract infections (UTI), one of the most common types infections causing significant health problems worldwide, uropathogens use TCSs for adaptation, survival, and establishment of pathogenicity. For example, uropathogens can exploit TCSs to survive inside bladder epithelial cells, sense osmolar variations in urine, promote their ascension along the urinary tract or even produce lytic enzymes resulting in exfoliation of the urothelium. Despite the usefulness of studying the function of TCSs in in vitro experimental models, it is of primary necessity to study bacterial gene regulation also in the context of host niches, each displaying its own biological, chemical, and physical features. In light of this, the aim of this review is to provide a concise description of several bacterial TCSs, whose activity has been described in mouse models of UTI.

Whole-genome analysis of Haemophilus influenzae strains isolated from persons with cystic fibrosis

Introduction. Haemophilus influenzae is a commensal of the respiratory tract that is frequently present in cystic fibrosis (CF) patients and may cause infection. Antibiotic resistance is well described for CF strains, and virulence factors have been proposed.Hypothesis/Gap. The genetic diversity of H. influenzae strains present in the lungs of persons with CF is largely unknown despite the fact that this organism is considered to be a pathogen in this condition. The aim was to establish the genetic diversity and susceptibility of H. influenzae strains from persons with CF, and to screen the whole genomes of these strains for the presence of antibiotic resistance determinants and proposed virulence factors.Methods. A total of 67 strains, recovered from respiratory samples from persons with CF from the UK (n=1), Poland (n=2), Spain (n=24) and the Netherlands (n=40), were subjected to whole-genome sequencing using Illumina technology and tested for antibiotic susceptibility. Forty-nine of these strains (one per different sequence type) were analysed for encoded virulence factors and resistance determinants.Results. The 67 strains represented 49 different sequence types. Susceptibility testing showed that all strains were susceptible to aztreonam, ciprofloxacin, imipenem and tetracycline. Susceptibility to ampicillin, ampicillin/sulbactam, amoxicillin/clavulanic acid, cefuroxime, cefixime, ceftriaxone, cefepime, meropenem, clarithromycin, co-trimoxazole and levofloxacin ranged from 70.2-98.5%. Only 6/49 strains (12.2%) harboured acquired resistance genes. Mutations associated with a ß-lactamase-negative ampicillin-resistant phenotype were present in four strains (8.2 %). The potential virulence factors, urease, haemoglobin- and haptoglobin-binding protein/carbamate kinase, and OmpP5 (OmpA), were encoded in more than half of the strains. The genes for HMW1, HMW2, H. influenzae adhesin, a IgA-specific serine endopeptidase autotransporter precursor, a TonB-dependent siderophore, an ABC-transporter ATP-binding protein, a methyltransferase, a BolA-family transcriptional regulator, glycosyltransferase Lic2B, a helix-turn-helix protein, an aspartate semialdehyde dehydrogenase and another glycosyltransferase were present in less than half of the strains.Conclusion. The H. influenzae strains showed limited levels of resistance, with the highest being against co-trimoxazole. Sequences encoding a carbamate kinase and a haemoglobin- and haemoglobin-haptoglobin-binding-like protein, a glycosyl transferase and an urease may aid the colonization of the CF lung. The adhesins and other identified putative virulence factors did not seem to be necessary for colonization.

Extended Bacteria Culture-Based Clustering Identifies a Phenotype Associating Increased Cough and Enterobacterales in Stable Chronic Obstructive Pulmonary Disease

Chronic obstructive pulmonary disease (COPD) is a chronic inflammatory lung disease characterized by airflow limitation. This chronic respiratory disease represents the third leading cause of death worldwide. Alteration of the airway microbiota has been reported to be associated with exacerbation frequency in COPD, but its role on the symptoms in patients at stable state is still incompletely described. This study aimed to determine whether bacteria isolated in sputum can be associated with the clinical features of COPD patients within stable state. Our study highlights, for the first time, that altered microbiota with Enterobacterales is associated with pejorative clinical symptoms in stable COPD patients. The airway microbiota of 38 patients was analyzed using an extended culture approach and mass spectrometry identification. Cluster analysis by principal coordinate analysis of the bacterial communities showed that the patients could be classified into three distinct clusters in our cohort. The clusters showed no differences in proportions of the phylum, but one of them was associated with a high prevalence of Enterobacterales (71.4% in cluster 1 vs. 0% in cluster 3), loss of microbiota diversity, and higher bacterial load (10⁷ vs. 10⁵ CFU/ml, respectively) and characterized by predominant cough and impact on mental health. These novel findings, supported by further studies, could lead to modifying the processing of COPD sputum in the everyday practice of clinical microbiology laboratories.

Effect of collagen and EPS components on the viscoelasticity of Pseudomonas aeruginosa biofilms

Pseudomonas aeruginosa is an opportunistic pathogen that causes thousands of deaths every year in part due to its ability to form biofilms composed of bacteria embedded in a matrix of self-secreted extracellular polysaccharides (EPS), e-DNA, and proteins. In chronic wounds, biofilms are exposed to the host extracellular matrix, of which collagen is a major component. How bacterial EPS interacts with host collagen and whether this interaction affects biofilm viscoelasticity is not well understood. Since physical disruption of biofilms is often used in their removal, knowledge of collagen's effects on biofilm viscoelasticity may enable new treatment strategies that are better tuned to biofilms growing in host environments. In this work, biofilms are grown in the presence of different concentrations of collagen that mimic in vivo conditions. In order to explore collagen's interaction with EPS, nine strains of P. aeruginosa with different patterns of EPS production were used to grow biofilms. Particle tracking microrheology was used to characterize the mechanical development of biofilms over two days. Collagen is found to decrease biofilm compliance and increase relative elasticity regardless of the EPS present in the system. However, this effect is minimized when biofilms overproduce EPS. Collagen appears to become a de facto component of the EPS, through binding to bacteria or physical entanglement.

Presence of the Hmq System and Production of 4-Hydroxy-3-Methyl-2-Alkylquinolines Are Heterogeneously Distributed between Burkholderia cepacia Complex Species and More Prevalent among Environmental than Clinical Isolates

The Burkholderia cepacia complex (Bcc) comprises several species of closely related, versatile bacteria. Some Bcc strains produce 4-hydroxy-3-methyl-2-alkylquinolines (HMAQs), analogous to the 4-hydroxy-2-alkylquinolines of Pseudomonas aeruginosa. Using in silico analyses, we previously estimated that the hmqABCDEFG operon, which encodes enzymes involved in the biosynthesis of HMAQs, is carried by about one-third of Bcc strains, with considerable inter- and intraspecies variability. In the present study, we investigated by PCR, using consensus primers, the distribution of hmqABCDEFG in a collection of 312 Bcc strains (222 of clinical and 90 of environmental origins) belonging to 18 Bcc species. We confirmed that this operon is not distributed evenly among Bcc species. Among the 30% of strains bearing the hmqABCDEFG operon, we found that 92% of environmental isolates and 82% of clinically isolated Bcc strains produce levels of HMAQs detectable by liquid chromatography-mass spectrometry in at least one of the tested culture conditions. Among the hmqABCDEFG-positive but HMAQ-negative strains, none expressed the hmqA gene under the specified culture conditions. Interestingly, the hmqABCDEFG operon is more prevalent among plant root environment species (e.g., Burkholderia ambifaria and Burkholderia cepacia) and absent in species commonly found in chronically colonized individuals with cystic fibrosis (e.g., Burkholderia cenocepacia and Burkholderia multivorans), suggesting a role for the Hmq system in niche adaptation. We investigated the impact of the Hmq system on plant growth promotion and found that Pisum sativum root development by B. ambifaria required a functional HMAQ system.

IMPORTANCE Environmental bacteria belonging to the various closely related species forming the Burkholderia cepacia complex (Bcc) can infect plants and animals, including humans. Their pathogenicity is regulated by intercellular communication, or quorum sensing, allowing them to collaborate instead of acting individually. Bcc organisms generally exploit interacting quorum sensing systems based on N-acyl-homoserine lactones as signaling molecules. Several Bcc strains also carry an hmqABCDEFG operon responsible for the biosynthesis of 4-hydroxy-3-methyl-2-alkylquinolines (HMAQs), molecules analogous to the Pseudomonas quinolone signal (PQS) system of P. aeruginosa. Our finding that the prevalences of the Hmq system and HMAQ production are very different between various Bcc species suggests a key role in niche adaptation or pathogenicity. This is supported by a significant reduction in plant growth promotion in the absence of HMAQ production for a beneficial Bcc strain.

An Overview on the Upper and Lower Airway Microbiome in Cystic Fibrosis Patients

BACKGROUND

In cystic fibrosis patients, the mucus is an excellent place for opportunistic bacteria and pathogens to cover. Chronic infections of upper and lower airways play a critical role in the mortality of cystic fibrosis. This study aimed to introduce the microbiota profiles in patients with cystic fibrosis.

MATERIALS AND METHODS

In this study, a comprehensive literature search was done for studies on upper and lower airway microbiota in cystic fibrosis patients. International and national databases were searched for the following MeSH words: microbiota, microbiome, upper airway, lower airway, cystic fibrosis, cystic fibrosis, upper airway microbiome, lower airway microbiome, microbiome pattern in cystic fibrosis, microbiome pattern in cystic fibrosis, upper airway microbiota, lower airway microbiota, and microbiota pattern.

RESULTS

Streptococcus spp. are in significantly higher relative abundance in infants and children with cystic fibrosis; however, Pseudomonas spp. are in higher relative abundance in adults with cystic fibrosis. Molecular diagnostic techniques can be remarkably accurate in detecting microbial strains.

CONCLUSION

For the detection and isolation of most bacterial species, independent-culture methods in addition to the standard culture method are recommended, and sampling should include both upper and lower airways.

Overproduction of the AlgT Sigma Factor Is Lethal to Mucoid Pseudomonas aeruginosa

Pseudomonas aeruginosa isolates from chronic lung infections often overproduce alginate, giving rise to the mucoid phenotype. Isolation of mucoid strains from chronic lung infections correlates with a poor patient outcome. The most common mutation that causes the mucoid phenotype is called mucA22 and results in a truncated form of the anti-sigma factor MucA that is continuously subjected to proteolysis. When a functional MucA is absent, the cognate sigma factor, AlgT, is no longer sequestered and continuously transcribes the alginate biosynthesis operon, leading to alginate overproduction. In this work, we report that in the absence of wild-type MucA, providing exogenous AlgT is toxic. This is intriguing, since mucoid strains endogenously possess high levels of AlgT. Furthermore, we show that suppressors of toxic AlgT production have mutations in mucP, a protease involved in MucA degradation, and provide the first atomistic model of MucP. Based on our findings, we speculate that mutations in mucP stabilize the truncated form of MucA22, rendering it functional and therefore able to reduce toxicity by properly sequestering AlgT.IMPORTANCE Pseudomonas aeruginosa is an opportunistic bacterial pathogen capable of causing chronic lung infections. Phenotypes important for the long-term persistence and adaption to this unique lung ecosystem are largely regulated by the AlgT sigma factor. Chronic infection isolates often contain mutations in the anti-sigma factor mucA, resulting in uncontrolled AlgT and continuous production of alginate in addition to the expression of ∼300 additional genes. Here, we report that in the absence of wild-type MucA, AlgT overproduction is lethal and that suppressors of toxic AlgT production have mutations in the MucA protease, MucP. Since AlgT contributes to the establishment of chronic infections, understanding how AlgT is regulated will provide vital information on how P. aeruginosa is capable of causing long-term infections.

Optimization of nitric oxide donors for investigating biofilm dispersal response in Pseudomonas aeruginosa clinical isolates

Pseudomonas aeruginosa biofilms contribute heavily to chronic lung infection in cystic fibrosis patients, leading to morbidity and mortality. Nitric oxide (NO) has been shown to disperse P. aeruginosa biofilms in vitro, ex vivo and in clinical trials as a promising anti-biofilm agent. Traditional NO donors such as sodium nitroprusside (SNP) have been extensively employed in different studies. However, the dosage of SNP in different studies was not consistent, ranging from 500 nM to 500 μM. SNP is light sensitive and produces cyanide, which may lead to data misinterpretation and inaccurate predictions of dispersal responses in clinical settings. New NO donors and NO delivery methods have therefore been explored. Here we assessed 7 NO donors using P. aeruginosa PAO1 and determined that SNP and Spermine NONOate (S150) successfully reduced > 60% biomass within 24 and 2 h, respectively. While neither dosage posed toxicity towards bacterial cells, chemiluminescence assays showed that SNP only released NO upon light exposure in M9 media and S150 delivered much higher performance spontaneously. S150 was then tested on 13 different cystic fibrosis P. aeruginosa (CF-PA) isolates; most CF-PA biofilms were significantly dispersed by 250 μM S150. Our work therefore discovered a commercially available NO donor S150, which disperses CF-PA biofilms efficiently within a short period of time and without releasing cyanide, as an alternative of SNP in clinical trials in the future. KEY POINTS: • S150 performs the best in dispersing P. aeruginosa biofilms among 7 NO donors. • SNP only releases NO in the presence of light, while S150 releases NO spontaneously. • S150 successfully disperses biofilms formed by P. aeruginosa cystic fibrosis clinical isolates.

Extracellular Vesicles from Pseudomonas aeruginosa Suppress MHC-Related Molecules in Human Lung Macrophages

Pseudomonas aeruginosa, a Gram-negative bacterium, is one of the most common pathogens colonizing the lungs of cystic fibrosis patients. P. aeruginosa secrete extracellular vesicles (EVs) that contain LPS and other virulence factors that modulate the host's innate immune response, leading to an increased local proinflammatory response and reduced pathogen clearance, resulting in chronic infection and ultimately poor patient outcomes. Lung macrophages are the first line of defense in the airway innate immune response to pathogens. Proper host response to bacterial infection requires communication between APC and T cells, ultimately leading to pathogen clearance. In this study, we investigate whether EVs secreted from P. aeruginosa alter MHC Ag expression in lung macrophages, thereby potentially contributing to decreased pathogen clearance. Primary lung macrophages from human subjects were collected via bronchoalveolar lavage and exposed to EVs isolated from P. aeruginosa in vitro. Gene expression was measured with the NanoString nCounter gene expression assay. DNA methylation was measured with the EPIC array platform to assess changes in methylation. P. aeruginosa EVs suppress the expression of 11 different MHC-associated molecules in lung macrophages. Additionally, we show reduced DNA methylation in a regulatory region of gene complement factor B (CFB) as the possible driving mechanism of widespread MHC gene suppression. Our results demonstrate MHC molecule downregulation by P. aeruginosa-derived EVs in lung macrophages, which is consistent with an immune evasion strategy employed by a prokaryote in a host-pathogen interaction, potentially leading to decreased pulmonary bacterial clearance.

Clinical characteristics and outcomes associated with Inquilinus infection in cystic fibrosis

BACKGROUND

Molecular diagnostics have led to the identification of a broad range of bacterial species in cystic fibrosis (CF) including Inquilinus. The clinical significance of Inquilinus in CF has not been thoroughly characterized.

METHODS

Retrospective, case-control study of persons with CF from two CF centers with at least one respiratory culture positive for Inquilinus spp. compared with age-matched CF controls with chronic Pseudomonas aeruginosa. Percent predicted forced expiratory volume in one second (ppFEV1) and body mass index percentile (BMI) were modeled from time of first positive culture up to 5 years later. Rates of pulmonary exacerbations were compared. Inquilinus isolates were genotyped to evaluate strain diversity.

RESULTS

Seventeen patients with Inquilinus infection were identified with a mean age of 13 years at first positive culture. Most cases had multiple cultures positive for Inquilinus. ppFEV1 was not different between cases versus controls (80.2% vs 81.6%, p = 0.97 at baseline, 67.5% vs. 73.3%, p = 0.82 at 5 years). Patients were undernourished and BMI percentiles did not differ between groups (30.7% vs 43.4%, p = 0.32 at baseline, 37.9% vs. 37.6%, p = 0.98 at 5 years). There was no difference in the pulmonary exacerbation rate (3.0/year vs 2.5/year, p = 0.34). Genotyping showed diverse genetic strains between patients.

CONCLUSIONS

Inquilinus can present in childhood and is often associated with chronic infection in CF. Lung function and nutrition status at time of detection, lung function decline, and pulmonary exacerbation rates in Inquilinus cases were similar to those with chronic P. aeruginosa, a well-established CF pathogen.

Nonmucoid gram-negative Pseudomonas rods can readily be observed in cystic fibrosis patients' smears stained by the PATS reaction

Cystic fibrosis(CF) is responsible for much of the chronic pulmonary disease seen in children. Progressive pulmonary insufficiency accompanied by respiratory tract infection is the cause of death in 90% of CF patients. Although gram-positive staphylococci were responsible for most of these pulmonary infections prior to 1960, gram-negative Pseudomonas aeruginosa(PA) colonization is now the major cause of the progressive pulmonary disease responsible for the morbidity and mortality in CF patients. Sputum has long been used for cultural purposes for CF patient evaluation. It has not been a good source for Gram stain specimens inasmuch as large numbers of deep blue gram-positive bacteria (Fig. 1) can overlie and mask the smaller numbers of pink or red rods such as PA which are being sought in the stained smear.

Antibacterial activity of iron oxide, iron nitride, and tobramycin conjugated nanoparticles against Pseudomonas aeruginosa biofilms

BACKGROUND

Novel methods are necessary to reduce morbidity and mortality of patients suffering from infections with Pseudomonas aeruginosa. Being the most common infectious species of the Pseudomonas genus, P. aeruginosa is the primary Gram-negative etiology responsible for nosocomial infections. Due to the ubiquity and high adaptability of this species, an effective universal treatment method for P. aeruginosa infection still eludes investigators, despite the extensive research in this area.

RESULTS

We report bacterial inhibition by iron-oxide (nominally magnetite) nanoparticles (NPs) alone, having a mean hydrodynamic diameter of ~ 16 nm, as well as alginate-capped iron-oxide NPs. Alginate capping increased the average hydrodynamic diameter to ~ 230 nm. We also investigated alginate-capped iron-oxide NP-drug conjugates, with a practically unchanged hydrodynamic diameter of ~ 232 nm. Susceptibility and minimum inhibitory concentration (MIC) of the NPs, NP-tobramycin conjugates, and tobramycin alone were determined in the PAO1 bacterial colonies. Investigations into susceptibility using the disk diffusion method were done after 3 days of biofilm growth and after 60 days of growth. MIC of all compounds of interest was determined after 60-days of growth, to ensure thorough establishment of biofilm colonies.

CONCLUSIONS

Positive inhibition is reported for uncapped and alginate-capped iron-oxide NPs, and the corresponding MICs are presented. We report zero susceptibility to iron-oxide NPs capped with polyethylene glycol, suggesting that the capping agent plays a major role in enabling bactericidal ability in of the nanocomposite. Our findings suggest that the alginate-coated nanocomposites investigated in this study have the potential to overcome the bacterial biofilm barrier. Magnetic field application increases the action, likely via enhanced diffusion of the iron-oxide NPs and NP-drug conjugates through mucin and alginate barriers, which are characteristic of cystic-fibrosis respiratory infections. We demonstrate that iron-oxide NPs coated with alginate, as well as alginate-coated magnetite-tobramycin conjugates inhibit P. aeruginosa growth and biofilm formation in established colonies. We have also determined that susceptibility to tobramycin decreases for longer culture times. However, susceptibility to the iron-oxide NP compounds did not demonstrate any comparable decrease with increasing culture time. These findings imply that iron-oxide NPs are promising lower-cost alternatives to silver NPs in antibacterial coatings, solutions, and drugs, as well as other applications in which microbial abolition or infestation prevention is sought.

Cystic Fibrosis and Pseudomonas aeruginosa: the Host-Microbe Interface

In human pathophysiology, the clash between microbial infection and host immunity contributes to multiple diseases. Cystic fibrosis (CF) is a classical example of this phenomenon, wherein a dysfunctional, hyperinflammatory immune response combined with chronic pulmonary infections wreak havoc upon the airway, leading to a disease course of substantial morbidity and shortened life span. Pseudomonas aeruginosa is an opportunistic pathogen that commonly infects the CF lung, promoting an accelerated decline of pulmonary function. Importantly, P. aeruginosa exhibits significant resistance to innate immune effectors and to antibiotics, in part, by expressing specific virulence factors (e.g., antioxidants and exopolysaccharides) and by acquiring adaptive mutations during chronic infection. In an effort to review our current understanding of the host-pathogen interface driving CF pulmonary disease, we discuss (i) the progression of disease within the primitive CF lung, specifically focusing on the role of host versus bacterial factors; (ii) critical, neutrophil-derived innate immune effectors that are implicated in CF pulmonary disease, including reactive oxygen species (ROS) and antimicrobial peptides (e.g., LL-37); (iii) P. aeruginosa virulence factors and adaptive mutations that enable evasion of the host response; and (iv) ongoing work examining the distribution and colocalization of host and bacterial factors within distinct anatomical niches of the CF lung.

Recent insights on nanomedicine for augmented infection control

Antimicrobial agents have been widely investigated for protecting against microbial infections in modern health. Drug-related limitations, poor bioavailability, toxicity to mammalian cells, and frequent bacteria drug resistance are major challenges faced when exploited in nanomedicine forms. Specific attention has been paid to control nanomaterial-based infection against numerous challenging pathogens in addition to improved drug delivery, targeting, and pharmacokinetic (PK) profiles, and thus, efficient antimicrobials have been fabricated using diverse components (metals, metal oxides, synthetic and semisynthetic polymers, natural or biodegradable polymers, etc). The present review covers several nanocarriers delivered through various routes of administration, highlighting major findings to control microbial infection as compared to using the free drug. Results over the past decade support the consistent development of various nanomedicines capable of improving biological significance and therapeutic benefits against an array of microbial strains. Depending on the intended application of nanomedicine, infection control will be challenged by various factors such as weighing the risk-benefits in healthcare settings, nanomaterial-induced (eco)toxicological hazards, frequent development of antibiotic resistance, scarcity of in vivo toxicity data, and a poor understanding of microbial interactions with nanomedicine at the molecular level. This review summarizes well-established informative data for nanomaterials used for infection control and safety concerns of nanomedicines to healthcare sectors followed by the significance of a unique "safe-by-design" approach.

Potential of the Burkholderia cepacia Complex to Produce 4-Hydroxy-3-Methyl-2-Alkyquinolines

A few Burkholderia species, especially Burkholderia pseudomallei, Burkholderia thailandensis, Burkholderia ambifaria, and Burkholderia cepacia, are known to produce and release various 4-hydroxy-3-methyl-2-alkylquinolines (HMAQs), a family of molecules analogous to the 4-hydroxy-2-alkylquinolines [aka 2-n-alkyl-4(1H)-quinolones] of Pseudomonas aeruginosa, which include the Pseudomonas quinolone signal (PQS). However, while these exoproducts play several roles in P. aeruginosa virulence and survival, the available literature is very limited on their distribution and function in Burkholderia. In this perspective article, we studied the distribution of the hmqABCDEFG operon, which encodes the enzymes involved in the biosynthesis of HMAQs, in the Burkholderia cepacia complex (Bcc) group. Based on the available sequence data, about one third of Bcc species carry a homolog of the hmqABCDEFG, and not all sequenced strains in a given species possess this operon. Looking at the synteny of genes surrounding the hmqABCDEFG operon, we found that for some species, the operon seems to have been deleted or replaced by other genes. Finally, we review the literature on the possible function of HMAQs. Understanding the Hmq system may provide clues concerning their functions in Bcc.

Remodeling of O Antigen in Mucoid Pseudomonas aeruginosa via Transcriptional Repression of wzz2

Detection of mucoid Pseudomonas aeruginosa, characterized by the overproduction of alginate, is correlated with the establishment of a chronic pulmonary infection and disease progression in people with cystic fibrosis (CF). In addition to the overproduction of alginate, loss of O antigen lipopolysaccharide production is also selected for in chronic infection isolates. In this study, we have identified the regulatory network that inversely regulates O antigen and alginate production. Understanding the regulation of these chronic phenotypes will elucidate mechanisms that are important for the establishment of a long-term P. aeruginosa lung infection and ultimately provide an opportunity for intervention. Preventing P. aeruginosa from chronically adapting to the CF lung environment could provide a better outcome for people who are infected.

Pseudomonas aeruginosa is an opportunistic pathogen that causes chronic lung infections in people with cystic fibrosis (CF). Chronic P. aeruginosa isolates generally do not express O antigen and often have a mucoid phenotype, which is characterized by the overproduction of the exopolysaccharide alginate. Therefore, O antigen expression and the mucoid phenotype may be coordinately regulated upon chronic adaption to the CF lung. Here we demonstrate that PDO300, a mucoid strain derived from the nonmucoid laboratory isolate PAO1, does not produce very long O antigen due to decreased expression of Wzz2, the very long O antigen chain length control protein, and that mucoid clinical isolates express reduced levels of Wzz2 compared to nonmucoid isolates. Further, we show that forcing the expression of very long O antigen by PDO300, by providing wzz2 in trans, does not alter alginate production, suggesting that sugar precursors are not limited between the two biosynthesis pathways. Moreover, we confirm that AmrZ, a transcription factor highly expressed in mucoid strains, is a negative regulator of wzz2 promoter activity and very long O antigen expression. These experiments identify the first transcriptional regulator of O antigen chain length in P. aeruginosa and support a model where transition to a chronic mucoid phenotype is correlated with downregulation of very long O antigen through decreased Wzz2 production.

The co-colonization prevalence of Pseudomonas aeruginosa and Aspergillus fumigatus in cystic fibrosis: A systematic review and meta-analysis

PURPOSE

The co-colonization prevalence of P. aeruginosa and A. fumigatus in cystic fibrosis (CF) has been inconsistently reported. The purpose of this systematic review and meta-analysis was to estimate the overall co-colonization prevalence of P. aeruginosa and A. fumigatus in CF.

METHODS

The Embase, PubMed and Web of Science databases were systematically searched for studies reporting the co-colonization prevalence of P. aeruginosa and A. fumigatus in CF. The co-colonization prevalence of two pathogenic microorganisms in the individual studies was assessed by calculating the proportion and 95% confidence interval (CI). The random effects model was used to calculate the pooled prevalence. The I² test was used to assess statistical heterogeneity. The funnel plot and two statistical methods were used to assess publication bias.

RESULTS

Twenty-three eligible studies were included in this analysis. The pooled co-colonization prevalence of P. aeruginosa and A. fumigatus in CF patients was 15.8% (95% CI: 9.9-21.8). The co-colonization prevalence of P. aeruginosa and A. fumigatus chronic colonization was lower than that of intermittent colonization, higher in sputum cultures than in bronchoalveolar lavage (BAL) cultures, and lower in children than in adults. There was a statistically significant difference in co-colonization prevalence among studies from different decades, but the prevalence was similar in different geographical regions and with different study types.

CONCLUSIONS

The co-colonization prevalence of P. aeruginosa and A. fumigatus in the lower respiratory tract of CF patients was high. The anti-infective treatment in exacerbation of CF should be considered to cover the two pathogenic microorganisms simultaneously. Large-scale research is still needed to obtain more accurate co-colonization data.

Recent Advances in the Development of Antimicrobial Nanoparticles for Combating Resistant Pathogens

The rapid growth of harmful pathogens and their multidrug-resistance poses a severe challenge for health professionals and for the development of new healthcare products. Various strategies are exploited for the development of effective antimicrobial agents, and nanoparticles are a particularly promising class of materials in this respect. This review summarizes recent advances in antimicrobial metallic, polymeric, and lipid-based nanoparticles such as liposomes, solid lipid nanoparticles, and nanostructured lipid carriers. The latter materials in particular are engineered for antimicrobial agent delivery and act by encapsulation, receptor-based binding, and disruption of microbial adherence to cellular substrates. Potential strategies for the design of multifunctional antimicrobial nanocarriers, combining material chemistry and biological interface science, are also discussed.

Development of the respiratory tract microbiota in cystic fibrosis

PURPOSE OF REVIEW

Progression of lung disease in cystic fibrosis (CF) is punctuated by Pseudomonas aeruginosa infection and recurrent pulmonary exacerbations, and is the major determinant of a patient's life expectancy. With the advent of novel deep-sequencing techniques, polymicrobial bacterial assemblages rather than single pathogens seem to be responsible for the deterioration of pulmonary function. This review summarizes recent insights into the development of the CF respiratory tract microbiome, with its determinants and its relations to clinical parameters.

RECENT FINDINGS

Research has moved from microbiota snapshots to intensive sampling over time, in an attempt to identify biomarkers of progression of CF lung disease. The developing respiratory tract microbiota in CF is perturbed by various endogenous and exogenous factors from the first months of life on. This work has revealed that both major pathogens such as P. aeruginosa and newly discovered players such as anaerobic species seem to contribute to CF lung disease. However, their interrelations remain to be unraveled.

SUMMARY

Long-term follow-up of microbiome development and alterations in relation to progression of lung disease and treatment is recommended. Moreover, integrating this information with other systems such as the metabolome, genome, mycome and virome is likely to contribute significantly to insights into host-microbiome interactions and thereby CF lung disease pathogenesis.

The detrimental impact of extracellular bacterial proteases on wound healing

In addition to clinical signs of infection (e.g. inflammation, purulence and pain), a microbial count of ≥10⁵ colony-forming units/g has historically been used to define wound infection. However, it is increasingly recognised that, rather than a high bioburden level alone being detrimental to wound healing, it is the virulence of the invading microorganism and the host's immune status that can affect clinical outcomes. Bacteria, such as Pseudomonas aeruginosa, Staphylococcus aureus and Staphylococcus epidermidis, have developed a range of virulence factors to help them overcome host defences and proliferate within the underlying soft tissue. More specifically, bacterial proteases are one such virulence factor that has been implicated in promoting the invasion and destruction of the host tissue. Because of the complexities of microorganisms, the proteases can negatively impact the wound environment, leading to delayed wound healing. The aim of the present paper is to describe various extracellular bacterial proteases; review the impact they have on the wound environment, the host immune response and biofilms; and discuss potential wound management strategies against them. The evidence discussed suggests that proteases may play a profound role in wound infections, contribute to the development of an inflammatory response and impede wound healing.

Bacterial infections in patients with primary ciliary dyskinesia: Comparison with cystic fibrosis

Primary ciliary dyskinesia (PCD) is an autosomal recessive disorder associated with severely impaired mucociliary clearance caused by defects in ciliary structure and function. Although recurrent bacterial infection of the respiratory tract is one of the major clinical features of this disease, PCD airway microbiology is understudied. Despite the differences in pathophysiology, assumptions about respiratory tract infections in patients with PCD are often extrapolated from cystic fibrosis (CF) airway microbiology. This review aims to summarize the current understanding of bacterial infections in patients with PCD, including infections with Pseudomonas aeruginosa, Staphylococcus aureus, and Moraxella catarrhalis, as it relates to bacterial infections in patients with CF. Further, we will discuss current and potential future treatment strategies aimed at improving the care of patients with PCD suffering from recurring bacterial infections.

Characterization of Inpatient Cystic Fibrosis Pulmonary Exacerbations

BACKGROUND AND OBJECTIVES

Pulmonary exacerbations lead to significant morbidity and mortality in patients with cystic fibrosis (CF). National consensus guidelines exist, but few studies report current practice in the treatment and monitoring of pulmonary exacerbations. The goal of this study was to characterize consistency and variability in the inpatient management of CF-related pulmonary exacerbations. We focused on the use of guideline-recommended maintenance therapies, antibiotic selection and treatment regimens, use of systemic corticosteroids, and frequency of lung function testing. We hypothesized that significant variability in these treatment practices exists nationally.

METHODS

This trial was a retrospective cross-sectional study. It included patients with CF aged ≤18 years hospitalized for pulmonary exacerbations between July 1, 2010, and June 30, 2015, at hospitals within the US Pediatric Health Information System database that are also Cystic Fibrosis Foundation-accredited care centers. One exacerbation per patient was randomly selected over the 5-year study period.

RESULTS

From 38 hospitals, 4827 individual pulmonary exacerbations were examined. Median length of stay was 10.0 days (interquartile range, 6-14.0 days). Significant variation was seen among centers in the use of hypertonic saline (11%-100%), azithromycin (5%-83%), and systemic corticosteroids (3%-61%) and in the frequency of lung function testing. Four different admission antibiotic regimens were used >10% of the time, and the most commonly used admission antibiotic regimen comprised 2 intravenous antibiotics with no additional oral or inhaled antibiotics (29%).

CONCLUSIONS

Significant variation exists in the treatment and monitoring of pulmonary exacerbations across Pediatric Health Information System-participating, Cystic Fibrosis Foundation-accredited care centers. Results from this study can inform future research working toward standardized inpatient pulmonary exacerbation management to improve CF care for children and adolescents.

Evolutionary adaptations of biofilms infecting cystic fibrosis lungs promote mechanical toughness by adjusting polysaccharide production

Biofilms are communities of microbes embedded in a matrix of extracellular polymeric substances, largely polysaccharides. Multiple types of extracellular polymeric substances can be produced by a single bacterial strain. The distinct polymer components of biofilms are known to provide chemical protection, but little is known about how distinct extracellular polysaccharides may also protect biofilms against mechanical stresses such as shear or phagocytic engulfment. Decades-long infections of Pseudomonas. aeruginosa biofilms in the lungs of cystic fibrosis patients are natural models for studies of biofilm fitness under pressure from antibiotics and the immune system. In cystic fibrosis infections, production of the extracellular polysaccharide alginate has long been known to increase with time and to chemically protect biofilms. More recently, it is being recognized that chronic cystic fibrosis infections also evolve to increase production of another extracellular polysaccharide, Psl; much less is known about Psl’s protective benefits to biofilms. We use oscillatory bulk rheology, on biofilms grown from longitudinal clinical isolates and from genetically-manipulated lab strains, to show that increased Psl stiffens biofilms and increases biofilm toughness, which is the energy cost to cause the biofilm to yield mechanically. Further, atomic force microscopy measurements reveal greater intercellular cohesion for higher Psl expression. Of the three types of extracellular polysaccharides produced by P. aeruginosa, only Psl increases the stiffness. Stiffening by Psl requires CdrA, a protein that binds to mannose groups on Psl and is a likely cross-linker for the Psl components of the biofilm matrix. We compare the elastic moduli of biofilms to the estimated stresses exerted by neutrophils during phagocytosis, and infer that increased Psl could confer a mechanical protection against phagocytic clearance.

Bacteria in lungs of people with cystic fibrosis can evolve through decades to build a tough biofilm that resists the body’s defences. Vernita Gordon and colleagues at the University of Texas, with co-workers in Europe, examined biofilms cultured from lung samples taken from patients at intervals over many years. The infecting bacterial populations had steadily evolved to increase production of specific carbohydrate components of the biofilms. The researchers found that increasing production of one carbohydrate component strengthens the biofilms, most likely due to the carbohydrate being crosslinked by protein molecules. The investigation suggests that the mechanics of the carbohydrate-protein network protects the biofilms from being broken into smaller pieces that can be engulfed by defensive cells called phagocytes. This new insight into the evolution of mechanical toughness complements the previously observed evolution of increasing chemical protection. Understanding these processes will assist efforts to combat them.

Cystic Fibrosis: Microbiology and Host Response

The earliest descriptions of lung disease in people with cystic fibrosis (CF) showed the involvement of 3 interacting pathophysiologic elements in CF airways: mucus obstruction, inflammation, and infection. Over the past 7 decades, our understanding of CF respiratory microbiology and inflammation has evolved with the introduction of new treatments, increased longevity, and increasingly sophisticated laboratory techniques. This article reviews the current understanding of infection and inflammation and their roles in CF lung disease. It also discusses how this constantly evolving information is used to inform current therapeutic strategies, measures and predictors of disease severity, and research priorities.

Candida albicans and Pseudomonas aeruginosa Interaction, with Focus on the Role of Eicosanoids

Candida albicans is commonly found in mixed infections with Pseudomonas aeruginosa, especially in the lungs of cystic fibrosis (CF) patients. Both of these opportunistic pathogens are able to form resistant biofilms and frequently infect immunocompromised individuals. The interaction between these two pathogens, which includes physical interaction as well as secreted factors, is mainly antagonistic. In addition, research suggests considerable interaction with their host, especially with immunomodulatory lipid mediators, termed eicosanoids. Candida albicans and Pseudomonas aeruginosa are both able to utilize arachidonic acid (AA), liberated from the host cells during infection, to form eicosanoids. The production of these eicosanoids, such as Prostaglandin E₂, by the host and the pathogens may affect the dynamics of polymicrobial infection and the outcome of infections. It is of considerable importance to elucidate the role of host-produced, as well as pathogen-produced eicosanoids in polymicrobial infection. This review will focus on in vitro as well as in vivo interaction between C. albicans and P. aeruginosa, paying special attention to the role of eicosanoids in the cross-talk between host and the pathogens.

Sensor kinase PA4398 modulates swarming motility and biofilm formation in Pseudomonas aeruginosa PA14

Pseudomonas aeruginosa is an opportunistic human pathogen that is able to sense and adapt to numerous environmental stimuli by the use of transcriptional regulators, including two-component regulatory systems. In this study, we demonstrate that the sensor kinase PA4398 is involved in the regulation of swarming motility and biofilm formation in P. aeruginosa PA14. APA4398 mutant strain was considerably impaired in swarming motility, while biofilm formation was increased by approximately 2-fold. The PA4398 mutant showed no changes in growth rate, rhamnolipid synthesis, or the production of the Pel exopolysaccharide but exhibited levels of the intracellular second messenger cyclic dimeric GMP (c-di-GMP) 50% higher than those in wild-type cells. The role of PA4398 in gene regulation was investigated by comparing the PA4398 mutant to the wildtype strain by using microarray analysis, which demonstrated that 64 genes were up- or downregulated more than 1.5-fold (P<0.05) under swarming conditions. In addition, more-sensitive real-time PCR studies were performed on genes known to be involved in c-di-GMP metabolism. Among the dysregulated genes were several involved in the synthesis and degradation of c-di-GMP or in the biosynthesis, transport, or function of the iron-scavenging siderophores pyoverdine and pyochelin, in agreement with the swarming phenotype observed. By analyzing additional mutants of selected pyoverdine- and pyochelin-related genes,we were able to show that not only pvdQ but also pvdR, fptA, pchA, pchD, and pchH are essential for the normal swarming behavior of P. aeruginosa PA14 and may also contribute to the swarming-deficient phenotype of the PA4398 mutant in addition to elevated c-di-GMP levels.

Culture-Based and Culture-Independent Bacteriologic Analysis of Cystic Fibrosis Respiratory Specimens

Cystic fibrosis (CF) is characterized by chronic infection and inflammation of the airways. In vitro culture of select bacterial species from respiratory specimens has been used to guide antimicrobial therapy in CF for the past few decades. More recently, DNA sequence-based, culture-independent approaches have been used to assess CF airway microbiology, although the role that these methods will (or should) have in routine microbiologic analysis of CF respiratory specimens is unclear. We performed DNA sequence analyses to detect bacterial species in 945 CF sputum samples that had been previously analyzed by selective CF culture. We determined the concordance of results based on culture and sequence analysis, highlighting the comparison of the results for the most prevalent genera. Although overall prevalence rates were comparable between the two methods, results varied by genus. While sequence analysis was more likely to detect Achromobacter, Stenotrophomonas, and Burkholderia, it was less likely to detect Staphylococcus. Streptococcus spp. were rarely reported in culture results but were the most frequently detected species by sequence analysis. A variety of obligate and facultative anaerobic species, not reported by culture, was also detected with high prevalence by sequence analysis. Sequence analysis indicated that in a considerable proportion of samples, taxa not reported by selective culture constituted a relatively high proportion of the total bacterial load, suggesting that routine CF culture may underrepresent significant segments of the bacterial communities inhabiting CF airways.

SNaPBceBcon: a Practical Tool for Identification and Genotyping of Burkholderia cepacia and Burkholderia contaminans

We propose an optimized protocol for an extensive population analysis of Burkholderia cepacia and Burkholderia contaminans. Seven new polymorphisms were added to the recently proposed SNaPBcen assay, and a total of 18 markers ensured the clear identification and distinction of B. cepacia and B. contaminans isolates and high genotypic discrimination (Simpson index of 0.94) compared to those for multilocus sequence typing.

Human genetic basis of interindividual variability in the course of infection

The key problem in human infectious diseases was posed at the turn of the 20th century: their pathogenesis. For almost any given virus, bacterium, fungus, or parasite, life-threatening clinical disease develops in only a small minority of infected individuals. Solving this infection enigma is important clinically, for diagnosis, prognosis, prevention, and treatment. Some microbes will inevitably remain refractory to, or escape vaccination, or chemotherapy, or both. The solution also is important biologically, because the emergence and evolution of eukaryotes alongside more rapidly evolving prokaryotes, archaea, and viruses posed immunological challenges of an ecological and evolutionary nature. We need to study these challenges in natural, as opposed to experimental, conditions, and also at the molecular and cellular levels. According to the human genetic theory of infectious diseases, inborn variants underlie life-threatening infectious diseases. Here I review the history of the field of human genetics of infectious diseases from the turn of the 19th century to the second half of the 20th century. This paper thus sets the scene, providing the background information required to understand and appreciate the more recently described monogenic forms of resistance or predisposition to specific infections discussed in a second paper in this issue.

Management of Pseudomonas aeruginosa infection in cystic fibrosis patients using inhaled antibiotics with a focus on nebulized liposomal amikacin

Pseudomonas aeruginosa (PsA) is a highly prevalent bacterial organism recovered from the lungs of cystic fibrosis (CF) patients and chronic PsA infection is linked to progressive pulmonary function decline. The eradication and treatment of this organism from CF airways is particularly challenging to CF care providers. Aerosolized antibiotics that target PsA help to slow down growth, maintain lung function and reduce the frequency of pulmonary exacerbations. In this review, we discuss the currently available inhaled antibiotics for management of PsA lung infections in CF patients, with a focus on liposomal amikacin for inhalation (LAI). LAI is a unique formulation of amikacin under development that enhances drug delivery and retention in CF airways via drug incorporation into neutral liposomes. Factors such as once-daily dosing, mucus and biofilm penetration and potentially prolonged off-drug periods make LAI a potentially attractive option to manage chronic PsA lung infections in CF patients.

Assessing Airway Microbiota in Cystic Fibrosis: What More Should Be Done?

The use of culture-independent methods has deepened our appreciation of the complexity of the bacterial communities that typically reside in the airways of persons with cystic fibrosis (CF). New insights into how changes in the structure of these communities relate to lung disease progression will likely raise expectations for more in-depth microbiologic analysis of CF respiratory specimens. An article in this issue of the Journal of Clinical Microbiology (W. G. Flight, A. Smith, C. Paisey, J. R. Marchesi, M. J. Bull, P. J. Norville, K. J. Mutton, A. K. Webb, R. J. Bright-Thomas, A. M. Jones, and E. Mahenthiralingam, J Clin Microbiol 53:2022-2029, 2015, http://dx.doi.org/10.1128/JCM.00432-15) describes the application of a culture-independent approach to the assessment of CF airway microbiota.

Comparison of microbiomes from different niches of upper and lower airways in children and adolescents with cystic fibrosis

Changes in the airway microbiome may be important in the pathophysiology of chronic lung disease in patients with cystic fibrosis. However, little is known about the microbiome in early cystic fibrosis lung disease and the relationship between the microbiomes from different niches in the upper and lower airways. Therefore, in this cross-sectional study, we examined the relationship between the microbiome in the upper (nose and throat) and lower (sputum) airways from children with cystic fibrosis using next generation sequencing. Our results demonstrate a significant difference in both α and β-diversity between the nose and the two other sampling sites. The nasal microbiome was characterized by a polymicrobial community while the throat and sputum communities were less diverse and dominated by a few operational taxonomic units. Moreover, sputum and throat microbiomes were closely related especially in patients with clinically stable lung disease. There was a high inter-individual variability in sputum samples primarily due to a decrease in evenness linked to increased abundance of potential respiratory pathogens such as Pseudomonas aeruginosa. Patients with chronic Pseudomonas aeruginosa infection exhibited a less diverse sputum microbiome. A high concordance was found between pediatric and adult sputum microbiomes except that Burkholderia was only observed in the adult cohort. These results indicate that an adult-like lower airways microbiome is established early in life and that throat swabs may be a good surrogate in clinically stable children with cystic fibrosis without chronic Pseudomonas aeruginosa infection in whom sputum sampling is often not feasible.

Oral streptococci and nitrite-mediated interference of Pseudomonas aeruginosa

The oral cavity harbors a diverse community of microbes that are physiologically unique. Oral microbes that exist in this polymicrobial environment can be pathogenic or beneficial to the host. Numerous oral microbes contribute to the formation of dental caries and periodontitis; however, there is little understanding of the role these microbes play in systemic infections. There is mounting evidence that suggests that oral commensal streptococci are cocolonized with Pseudomonas aeruginosa during cystic fibrosis pulmonary infections and that the presence of these oral streptococci contributes to improved lung function. The goal of this study was to examine the underlying mechanism by which Streptococcus parasanguinis antagonizes pathogenic P. aeruginosa. In this study, we discovered that oral commensal streptococci, including Streptococcus parasanguinis, Streptococcus sanguinis, and Streptococcus gordonii, inhibit the growth of P. aeruginosa and that this inhibition is mediated by the presence of nitrite and the production of hydrogen peroxide (H2O2) by oral streptococci. The requirement of both H2O2 and nitrite for the inhibition of P. aeruginosa is due to the generation of reactive nitrogenous intermediates (RNI), including peroxynitrite. Transposon mutagenesis showed that a P. aeruginosa mutant defective in a putative ABC transporter permease is resistant to both streptococcus/nitrite- and peroxynitrite-mediated killing. Furthermore, S. parasanguinis protects Drosophila melanogaster from killing by P. aeruginosa in a nitrite-dependent manner. Our findings suggest that the combination of nitrite and H2O2 may represent a unique anti-infection strategy by oral streptococci during polymicrobial infections.

Nanoengineered drug delivery systems for enhancing antibiotic therapy

Formulation scientists are recognizing nanoengineered drug delivery systems as an effective strategy to overcome limitations associated with antibiotic drug therapy. Antibiotics encapsulated into nanodelivery systems will contribute to improved management of patients with various infectious diseases and to overcoming the serious global burden of antibiotic resistance. An extensive review of several antibiotic-loaded nanocarriers that have been formulated to target drugs to infectious sites, achieve controlled drug release profiles, and address formulation challenges, such as low-drug entrapment efficiencies, poor solubility and stability is presented in this paper. The physicochemical properties and the in vitro/in vivo performances of various antibiotic-loaded delivery systems, such as polymeric nanoparticles, micelles, dendrimers, liposomes, solid lipid nanoparticles, lipid-polymer hybrid nanoparticles, nanohybirds, nanofibers/scaffolds, nanosheets, nanoplexes, and nanotubes/horn/rods and nanoemulsions, are highlighted and evaluated. Future studies that will be essential to optimize formulation and commercialization of these antibiotic-loaded nanosystems are also identified. The review presented emphasizes the significant formulation progress achieved and potential that novel nanoengineered antibiotic drug delivery systems have for enhancing the treatment of patients with a range of infections.

Levofloxacin inhalation solution for the treatment of chronic Pseudomonas aeruginosa infection among patients with cystic fibrosis

Chronic pulmonary infections are common among patients with cystic fibrosis. By 10 years of age, Pseudomonas aeruginosa is the predominant pathogen. Inhaled levofloxacin solution (MP-376) is a promising new therapy that exhibits rapid antibacterial activity and excellent biofilm penetration against P. aeruginosa. In the largest trial to date, 151 patients were randomized to receive MP-376 or placebo. At the end of the 28-day treatment period, patients who received MP-376 had decreased P. aeruginosa density in sputum, improved lung function parameters and improved respiratory symptoms. MP-376 also appeared to be safe and well tolerated. The results of two recently completed Phase III trials have not yet been released; however, these data will be critical in determining whether MP-376 is a safe and effective maintenance therapy for chronic pulmonary P. aeruginosa infections among patients with cystic fibrosis.

Characterization of Streptococcus pneumoniae clones from paediatric patients with cystic fibrosis

The role of Streptococcus pneumoniae in cystic fibrosis (CF) is poorly understood. The pneumococcal population has changed over time after the introduction of the heptavalent conjugate vaccine (PCV7) and, more recently, the 13-valent conjugate vaccine (PCV13). Although serotypes and clones causing invasive pneumococcal disease or colonizing healthy children have been extensively analysed, little is known so far on the serotypes and clones of pneumococci in CF patients. The aim of this work was to investigate serotypes, antibiotic susceptibilities, genotypes and biofilm production of CF pneumococcal isolates. Overall, 44 S. pneumoniae strains collected from 32 paediatric CF patients from January 2010 to May 2012 in a large Italian CF Centre were tested for antimicrobial susceptibility testing by Etest, serotyped by the Quellung reaction and genotyped by a combination of different molecular typing methods, including pbp gene restriction profiling, pspA restriction profiling and sequencing, PFGE and multilocus sequence typing. Biofilm production by pneumococcal strains was also assessed. Penicillin non-susceptibility was 16 %. High resistance rates (>56 %) were observed for erythromycin, clindamycin and tetracycline. The most frequent serotype recovered was serotype 3 (31.8 %). The coverage of PCV7 and PCV13 was 6.8 and 47.7 %, respectively. More than 80 % of CF strains belonged to Pneumococcal Molecular Epidemiology Network (PMEN) reference clones, the most common being Netherlands(3)-ST180 (28.2 %), and Greece(21)-30/ST193 (15.4 %). All strains produced biofilm in vitro, although with large variability in biofilm formation efficiency. No correlation was found between biofilm levels and serotype, clone or antibiotic resistance. The high isolation rate of antibiotic-resistant serotype 3 pneumococci from CF patients suggests that PCV13 could increase protection from pneumococcal colonization and infection.

BdlA, DipA and induced dispersion contribute to acute virulence and chronic persistence of Pseudomonas aeruginosa

The human pathogen Pseudomonas aeruginosa is capable of causing both acute and chronic infections. Differences in virulence are attributable to the mode of growth: bacteria growing planktonically cause acute infections, while bacteria growing in matrix-enclosed aggregates known as biofilms are associated with chronic, persistent infections. While the contribution of the planktonic and biofilm modes of growth to virulence is now widely accepted, little is known about the role of dispersion in virulence, the active process by which biofilm bacteria switch back to the planktonic mode of growth. Here, we demonstrate that P. aeruginosa dispersed cells display a virulence phenotype distinct from those of planktonic and biofilm cells. While the highest activity of cytotoxic and degradative enzymes capable of breaking down polymeric matrix components was detected in supernatants of planktonic cells, the enzymatic activity of dispersed cell supernatants was similar to that of biofilm supernatants. Supernatants of non-dispersing ΔbdlA biofilms were characterized by a lack of many of the degradative activities. Expression of genes contributing to the virulence of P. aeruginosa was nearly 30-fold reduced in biofilm cells relative to planktonic cells. Gene expression analysis indicated dispersed cells, while dispersing from a biofilm and returning to the single cell lifestyle, to be distinct from both biofilm and planktonic cells, with virulence transcript levels being reduced up to 150-fold compared to planktonic cells. In contrast, virulence gene transcript levels were significantly increased in non-dispersing ΔbdlA and ΔdipA biofilms compared to wild-type planktonic cells. Despite this, bdlA and dipA inactivation, resulting in an inability to disperse in vitro, correlated with reduced pathogenicity and competitiveness in cross-phylum acute virulence models. In contrast, bdlA inactivation rendered P. aeruginosa more persistent upon chronic colonization of the murine lung, overall indicating that dispersion may contribute to both acute and chronic infections.

Pathogenic bacteria, including the human pathogen Pseudomonas aeruginosa, can cause acute and chronic infections. The difference in these infection modes can be explained by how bacteria grow. Acute infections occur when individual bacteria rapidly replicate, produce high levels of virulence factors, and disseminate from the nidus of infection. Chronic infections occur when bacteria adhere to tissue or implanted medical devices and form multi-cellular, matrix-encased aggregates known as biofilms. The acute-to-chronic infection switch occurs when bacteria transition from planktonic to biofilm growth. However, the contribution of dispersion, the process by which bacteria leave a biofilm to return to planktonic growth, remains unclear. Here, we demonstrate that, while having left a biofilm, dispersed cells are distinct from planktonic cells with respect to gene expression, release of matrix-degrading enzymes, and pathogenicity. We found that a mutant impaired in nutrient-induced dispersion, while enhancing chronic infections, is impaired in mounting acute infections in both plant and mouse hosts. Overall, this work establishes that dispersed cells have a unique virulence phenotype, with nutrient-induced dispersion not only serving as an integral part of both acute and chronic infections but also as a potential mechanism of infection control.

Pseudomonas aeruginosa phenotypes associated with eradication failure in children with cystic fibrosis

BACKGROUND

Pseudomonas aeruginosa is a key respiratory pathogen in people with cystic fibrosis (CF). Due to its association with lung disease progression, initial detection of P. aeruginosa in CF respiratory cultures usually results in antibiotic treatment with the goal of eradication. Pseudomonas aeruginosa exhibits many different phenotypes in vitro that could serve as useful prognostic markers, but the relative relationships between these phenotypes and failure to eradicate P. aeruginosa have not been well characterized.

METHODS

We measured 22 easily assayed in vitro phenotypes among the baseline P. aeruginosa isolates collected from 194 participants in the 18-month EPIC clinical trial, which assessed outcomes after antibiotic eradication therapy for newly identified P. aeruginosa. We then evaluated the associations between these baseline isolate phenotypes and subsequent outcomes during the trial, including failure to eradicate after antipseudomonal therapy, emergence of mucoidy, and occurrence of an exacerbation.

RESULTS

Baseline P. aeruginosa isolates frequently exhibited phenotypes thought to represent chronic adaptation, including mucoidy. Wrinkly colony surface and irregular colony edges were both associated with increased risk of eradication failure (hazard ratios [95% confidence intervals], 1.99 [1.03-3.83] and 2.14 [1.32-3.47], respectively). Phenotypes reflecting defective quorum sensing were significantly associated with subsequent mucoidy, but no phenotype was significantly associated with subsequent exacerbations during the trial.

CONCLUSIONS

Pseudomonas aeruginosa phenotypes commonly considered to reflect chronic adaptation were observed frequently among isolates at early detection. We found that 2 easily assayed colony phenotypes were associated with failure to eradicate after antipseudomonal therapy, both of which have been previously associated with altered biofilm formation and defective quorum sensing.

Release of cystic fibrosis airway inflammatory markers from Pseudomonas aeruginosa-stimulated human neutrophils involves NADPH oxidase-dependent extracellular DNA trap formation

Cystic fibrosis (CF) airways are characterized by bacterial infections, excess mucus production, and robust neutrophil recruitment. The main CF airway pathogen is Pseudomonas aeruginosa. Neutrophils are not capable of clearing the infection. Neutrophil primary granule components, myeloperoxidase (MPO) and human neutrophil elastase (HNE), are inflammatory markers in CF airways, and their increased levels are associated with poor lung function. Identifying the mechanism of MPO and HNE release from neutrophils is of high clinical relevance for CF. In this article, we show that human neutrophils release large amounts of neutrophil extracellular traps (NETs) in the presence of P. aeruginosa. Bacteria are entangled in NETs and colocalize with extracellular DNA. MPO, HNE, and citrullinated histone H4 are all associated with DNA in Pseudomonas-triggered NETs. Both laboratory standard strains and CF isolates of P. aeruginosa induce DNA, MPO, and HNE release from human neutrophils. The increase in peroxidase activity of neutrophil supernatants after Pseudomonas exposure indicates that enzymatically active MPO is released. P. aeruginosa induces a robust respiratory burst in neutrophils that is required for extracellular DNA release. Inhibition of the cytoskeleton prevents Pseudomonas-initiated superoxide production and DNA release. NADPH oxidase inhibition suppresses Pseudomonas-induced release of active MPO and HNE. Blocking MEK/ERK signaling results in only minimal inhibition of DNA release induced by Pseudomonas. Our data describe in vitro details of DNA, MPO, and HNE release from neutrophils activated by P. aeruginosa. We propose that Pseudomonas-induced NET formation is an important mechanism contributing to inflammatory conditions characteristic of CF airways.