Metabolism and Pathogenicity of Pseudomonas aeruginosa Infections in the Lungs of Individuals with Cystic Fibrosis

Atomic force microscopy analysis of Pel polysaccharide- and type IV pili-mediated adhesion of Pseudomonas aeruginosa PA14 to an abiotic surface

Type IV pili (TFP) contribute to the ability of microbes such as Pseudomonas aeruginosa to engage with and move across surfaces. We reported previously that P. aeruginosa TFP generate retractive forces of ∼30 pN and provided indirect evidence that TFP-mediated surface attachment was enhanced in the presence of the Pel polysaccharide. Here, we use different mutants defective in flagellar, Pel production or TFP production - alone or in combination - to decipher the relative contribution of these biofilm-promoting factors for P. aeruginosa adhesion. By means of atomic force microscopy (AFM), we show that mutating the flagellum (ΔflgK mutant) results in an increase in Pel polysaccharide production, but this increase in Pel does not result in an increase in surface adhesive properties compared to those previously described for the WT strain. By blocking Pel production in the ΔflgK mutant (ΔflgKΔpel), we directly show that TFP play a major role in the adhesion of the bacteria to hydrophobic AFM tips, but that the adhesion force is only slightly impaired by the absence of Pel. Inversely, performing single-cell force spectroscopy measurements with the mutant lacking TFP (ΔflgKΔpilA) reveals that the Pel can modulate the attachment of the bacteria to a hydrophobic substrate in a time-dependent manner. Finally, little adhesion was detected for the ΔflgKΔpilAΔpelA triple mutant, suggesting that both TFP and Pel polysaccharide make a substantial contribution to bacteria-substratum interaction events. Altogether, our data allow us to decipher the relative contribution of Pel and TFP in the early attachment by P. aeruginosa.

Antimicrobial resistance survey and whole-genome analysis of nosocomial P. Aeruginosa isolated from eastern Province of China in 2016-2021

BACKGROUND

Pseudomonas aeruginosa is a major Gram-negative pathogen that can exacerbate lung infections in the patients with cystic fibrosis, which can ultimately lead to death.

METHODS

From 2016 to 2021, 103 strains of P. aeruginosa were isolated from hospitals and 20 antibiotics were used for antimicrobial susceptibility determination. Using next-generation genome sequencing technology, these strains were sequenced and analyzed in terms of serotypes, ST types, and resistance genes for epidemiological investigation.

RESULTS

The age distribution of patients ranged from 10 days to 94 years with a median age of 69 years old. The strains were mainly isolated from sputum (72 strains, 69.9%) and blood (14 strains, 13.6%). The size of these genomes ranged from 6.2 Mb to 7.4 Mb, with a mean value of 6.5 Mb. In addition to eight antibiotics that show inherent resistance to P. aeruginosa, the sensitivity rates for colistin, amikacin, gentamicin, ceftazidime, piperacillin, piperacillin-tazobactam, ciprofloxacin, meropenem, aztreonam, imipenem, cefepime and levofloxacin were 100%, 95.15%, 86.41%, 72.82%, 71.84%, 69.90%, 55.34%, 52.43%, 50.49%, 50.49%, 49.51% and 47.57% respectively, and the carriage rate of MDR strains was 30.69% (31/101). Whole-genome analysis showed that a total of 50 ST types were identified, with ST244 (5/103) and ST1076 (4/103) having a more pronounced distribution advantage. Serotype predictions showed that O6 accounted for 29.13% (30/103), O11 for 23.30% (24/103), O2 for 18.45% (19/103), and O1 for 11.65% (12/103) of the highest proportions. Notably, we found a significantly higher proportion of ExoU in P. aeruginosa strains of serotype O11 than in other cytotoxic exoenzyme positive strains. In addition to this, a total of 47 crpP genes that mediate resistance to fluoroquinolones antibiotics were found distributed on 43 P. aeruginosa strains, and 10 new variants of CrpP were identified, named 1.33, 1.34, 1.35, 1.36, 1.37, 1.38, 1.39, 1.40, 1.41 and 7.1.

CONCLUSIONS

We investigated the antibiotic susceptibility of clinical isolates of P. aeruginosa and genomically enriched the diversity of P. aeruginosa for its prophylactic and therapeutic value.

Pf4 Phage Variant Infection Reduces Virulence-Associated Traits in Pseudomonas aeruginosa

Pf4 is a filamentous bacteriophage integrated as a prophage into the genome of Pseudomonas aeruginosa PAO1. Pf4 virions can be produced without killing P. aeruginosa. However, cell lysis can occur during superinfection when Pf virions successfully infect a host lysogenized by a Pf superinfective variant. We have previously shown that infection of P. aeruginosa PAO1 with a superinfective Pf4 variant abolished twitching motility and altered biofilm architecture. More precisely, most of the cells embedded into the biofilm were showing a filamentous morphology, suggesting the activation of the cell envelope stress response involving both AlgU and SigX extracytoplasmic function sigma factors. Here, we show that Pf4 variant infection results in a drastic dysregulation of 3,360 genes representing about 58% of P. aeruginosa genome; of these, 70% of the virulence factors encoding genes show a dysregulation. Accordingly, Pf4 variant infection (termed Pf4*) causes in vivo reduction of P. aeruginosa virulence and decreased production of N-acyl-homoserine lactones and 2-alkyl-4-quinolones quorum-sensing molecules and related virulence factors, such as pyocyanin, elastase, and pyoverdine. In addition, the expression of genes involved in metabolism, including energy generation and iron homeostasis, was affected, suggesting further relationships between virulence and central metabolism. Altogether, these data show that Pf4 phage variant infection results in complex network dysregulation, leading to reducing acute virulence in P. aeruginosa. This study contributes to the comprehension of the bacterial response to filamentous phage infection. IMPORTANCE Filamentous bacteriophages can become superinfective and infect P. aeruginosa, even though they are inserted in the genome as lysogens. Despite this productive infection, growth of the host is only mildly affected, allowing the study of the interaction between the phage and the host, which is not possible in the case of lytic phages killing rapidly their host. Here, we demonstrate by transcriptome and phenotypic analysis that the infection by a superinfective filamentous phage variant causes a massive disruption in gene expression, including those coding for virulence factors and metabolic pathways.

Bacteriophage-Loaded Poly(lactic-co-glycolic acid) Microparticles Mitigate Staphylococcus aureus Infection and Cocultures of Staphylococcus aureus and Pseudomonas aeruginosa

Lung infections caused by Gram-positive Staphylococcus aureus (S. aureus) and coinfections caused by S. aureus and Gram-negative Pseudomonas aeruginosa (P. aeruginosa) are challenging to treat, especially with the rise in the number of antibiotic-resistant strains of these pathogens. Bacteriophage (phage) are bacteria-specific viruses that can infect and lyse bacteria, providing a potentially effective therapy for bacterial infections. However, the development of bacteriophage therapy is impeded by limited suitable biomaterials that can facilitate effective delivery of phage to the lung. Here, the ability of porous microparticles engineered from poly(lactic-co-glycolic acid) (PLGA), a biodegradable polyester, to effectively deliver phage to the lung, is demonstrated. The phage-loaded microparticles (phage-MPs) display potent antimicrobial efficacy against various strains of S. aureus in vitro and in vivo, and arrest the growth of a clinical isolate of S. aureus in the presence of sputum supernatant obtained from cystic fibrosis patients. Moreover, phage-MPs efficiently mitigate in vitro cocultures of S. aureus and P. aeruginosa and display excellent cytocompatibility with human lung epithelial cells. Therefore, phage-MPs represents a promising therapy to treat bacterial lung infection.

Structural insights into the substrate-bound condensation domains of non-ribosomal peptide synthetase AmbB

Non-ribosomal peptide synthetases (NRPS) are multi-modular/domain enzymes that catalyze the synthesis of bioactive peptides. A crucial step in the process is peptide elongation accomplished by the condensation (C) domain with the aid of a peptidyl carrier or thiolation (T) domain. Here, we examined condensation reaction carried out by NRPS AmbB involved in biosynthesis of l-2-amino-4-methoxy-trans-3-butenoic acid (AMB) in P. aeruginosa. We determined crystal structures of the truncated T–C bidomain of AmbB in three forms, the apo enzyme with disordered T domain, the holo form with serine linked phosphopantetheine (Ppant) and a holo form with substrate (l-alanine) loaded onto Ppant. The two holo forms feature the T domain in a substrate-donation conformation. Mutagenesis combined with functional assays identified residues essential for the attachment of Ppant, anchoring the Ppant-l-Ala in the donor catalytic channel and the role of the conserved His953 in condensation activity. Altogether, these results provide structural insights into the condensation reaction at the donor site with a substrate-bound C domain of AmbB and lay the foundation for understanding the molecular mechanism of condensation which is crucial for AMB synthesis.

Genomic and Metabolic Characteristics of the Pathogenicity in Pseudomonas aeruginosa

In recent years, the effectiveness of antimicrobials in the treatment of Pseudomonas aeruginosa infections has gradually decreased. This pathogen can be observed in several clinical cases, such as pneumonia, urinary tract infections, sepsis, in immunocompromised hosts, such as neutropenic cancer, burns, and AIDS patients. Furthermore, Pseudomonas aeruginosa causes diseases in both livestock and pets. The highly flexible and versatile genome of P. aeruginosa allows it to have a high rate of pathogenicity. The numerous secreted virulence factors, resulting from its numerous secretion systems, the multi-resistance to different classes of antibiotics, and the ability to produce biofilms are pathogenicity factors that cause numerous problems in the fight against P. aeruginosa infections and that must be better understood for an effective treatment. Infections by P. aeruginosa represent, therefore, a major health problem and, as resistance genes can be disseminated between the microbiotas associated with humans, animals, and the environment, this issue needs be addressed on the basis of an One Health approach. This review intends to bring together and describe in detail the molecular and metabolic pathways in P. aeruginosa's pathogenesis, to contribute for the development of a more targeted therapy against this pathogen.

E-Cigarette Use: Device Market, Study Design, and Emerging Evidence of Biological Consequences

Electronic cigarettes are frequently viewed as a safer alternative to conventional cigarettes; however, evidence to support this perspective has not materialized. Indeed, the current literature reports that electronic cigarette use is associated with both acute lung injury and subclinical dysfunction to the lung and vasculature that may result in pathology following chronic use. E-cigarettes can alter vascular dynamics, polarize innate immune populations towards a proinflammatory state, compromise barrier function in the pulmonary endothelium and epithelium, and promote pre-oncogenic phenomena. This review will summarize the variety of e-cigarette products available to users, discuss current challenges in e-cigarette study design, outline the range of pathologies occurring in cases of e-cigarette associated acute lung injury, highlight disease supporting tissue- and cellular-level changes resulting from e-cigarette exposure, and briefly examine how these changes may promote tumorigenesis. Continued research of the mechanisms by which e-cigarettes induce pathology benefit users and clinicians by resulting in increased regulation of vaping devices, informing treatments for emerging diseases e-cigarettes produce, and increasing public awareness to reduce e-cigarette use and the onset of preventable disease.

A Shift in Central Metabolism Accompanies Virulence Activation in Pseudomonas aeruginosa

The availability of energy has significant impact on cell physiology. However, the role of cellular metabolism in bacterial pathogenesis is not understood. We investigated the dynamics of central metabolism during virulence induction by surface sensing and quorum sensing in early-stage biofilms of the multidrug-resistant bacterium Pseudomonas aeruginosa We established a metabolic profile for P. aeruginosa using fluorescence lifetime imaging microscopy (FLIM), which reports the activity of NADH in live cells. We identified a critical growth transition period during which virulence is activated. We performed FLIM measurements and direct measurements of NADH and NAD+ concentrations during this period. Here, planktonic (low-virulence) and surface-attached (virulence-activated) populations diverged into distinct metabolic states, with the surface-attached population exhibiting FLIM lifetimes that were associated with lower levels of enzyme-bound NADH and decreasing total NAD(H) production. We inhibited virulence by perturbing central metabolism using citrate and pyruvate, which further decreased the enzyme-bound NADH fraction and total NAD(H) production and suggested the involvement of the glyoxylate pathway in virulence activation in surface-attached populations. In addition, we induced virulence at an earlier time using the electron transport chain oxidase inhibitor antimycin A. Our results demonstrate the use of FLIM to noninvasively measure NADH dynamics in biofilms and suggest a model in which a metabolic rearrangement accompanies the virulence activation period.IMPORTANCE The rise of antibiotic resistance requires the development of new strategies to combat bacterial infection and pathogenesis. A major direction has been the development of drugs that broadly target virulence. However, few targets have been identified due to the species-specific nature of many virulence regulators. The lack of a virulence regulator that is conserved across species has presented a further challenge to the development of therapeutics. Here, we identify that NADH activity has an important role in the induction of virulence in the pathogen P. aeruginosa This finding, coupled with the ubiquity of NADH in bacterial pathogens, opens up the possibility of targeting enzymes that process NADH as a potential broad antivirulence approach.

Virulence attenuating combination therapy: a potential multi-target synergy approach to treat Pseudomonas aeruginosa infections in cystic fibrosis patients

The World Health Organization considers the discovery of new treatments for P. aeruginosa a top priority. Virulence attenuating combination therapy (VACT) is a pragmatic strategy to improve bacterial clearance, repurpose outmoded antibiotics, improve drug efficacy at lower doses, and reduce the evolution of resistance. In vitro and in vivo studies have shown that adding a quorum sensing inhibitor or an extracellular polymeric substance repressor to classical antibiotics synergistically improves antipseudomonal activity. This review highlights why VACT could specifically benefit cystic fibrosis patients harboring chronic P. aeruginosa infections, outlines the current landscape of synergistic combinations between virulence-targeting small-molecules and anti-pseudomonal drugs, and suggests future directions for VACT research.

Intraclonal competitive fitness of longitudinal cystic fibrosis Pseudomonas aeruginosa airway isolates in liquid cultures

The metabolically versatile Pseudomonas aeruginosa inhabits biotic and abiotic environments including the niche of cystic fibrosis (CF) airways. This study investigated how the adaptation to CF lungs affects the within-clone fitness of P. aeruginosa to grow and persist in liquid cultures in the presence of the clonal ancestors. Longitudinal clonal P. aeruginosa isolates that had been collected from 12 CF donors since the onset of colonization for up to 30 years was subjected to within-clone competition experiments. The relative quantities of individual strains were determined by marker-free amplicon sequencing of multiplex PCR products of strain-specific nucleotide sequence variants, a novel method that is generally applicable to studies in evolutionary genetics and microbial ecology with real-world strain collections. For 10 of the 12 examined patient courses, P. aeruginosa isolates of the first years of colonization grew faster in the presence of their clonal progeny than alone. Single growth of individual strains showed no temporal trend with colonization time, but in co-culture, the early isolates out-competed their clonal progeny. Irrespective of the genetic make-up of the clone and its genomic microevolution in CF lungs, the early isolates expressed fitness traits to win the within-clone competition that were absent in their progeny.

Glutaminyl-tRNA Synthetase from Pseudomonas aeruginosa: Characterization, structure, and development as a screening platform

Pseudomonas aeruginosa has a high potential for developing resistance to multiple antibiotics. The gene (glnS) encoding glutaminyl-tRNA synthetase (GlnRS) from P. aeruginosa was cloned and the resulting protein characterized. GlnRS was kinetically evaluated and the K_M and k_cat ^obs , governing interactions with tRNA, were 1.0 μM and 0.15 s^-1 , respectively. The crystal structure of the α₂ form of P. aeruginosa GlnRS was solved to 1.9 Å resolution. The amino acid sequence and structure of P. aeruginosa GlnRS were analyzed and compared to that of GlnRS from Escherichia coli. Amino acids that interact with ATP, glutamine, and tRNA are well conserved and structure overlays indicate that both GlnRS proteins conform to a similar three-dimensional structure. GlnRS was developed into a screening platform using scintillation proximity assay technology and used to screen ~2,000 chemical compounds. Three inhibitory compounds were identified and analyzed for enzymatic inhibition as well as minimum inhibitory concentrations against clinically relevant bacterial strains. Two of the compounds, BM02E04 and BM04H03, were selected for further studies. These compounds displayed broad-spectrum antibacterial activity and exhibited moderate inhibitory activity against mutant efflux deficient strains of P. aeruginosa and E. coli. Growth of wild-type strains was unaffected, indicating that efflux was likely responsible for the lack of sensitivity. The global mode of action was determined using time-kill kinetics. BM04H03 did not inhibit the growth of human cell cultures at any concentration and BM02E04 only inhibit cultures at the highest concentration tested (400 μg/ml). In conclusion, GlnRS from P. aeruginosa is shown to have a structure similar to that of E. coli GlnRS and two natural product compounds were identified as inhibitors of P. aeruginosa GlnRS with the potential for utility as lead candidates in antibacterial drug development in a time of increased antibiotic resistance.

Interplay between host-microbe and microbe-microbe interactions in cystic fibrosis

The respiratory tract of individuals with cystic fibrosis is host to polymicrobial infections that persist for decades and lead to significant morbidity and mortality. Improving our understanding of CF respiratory infections requires coordinated efforts from researchers in the fields of microbial physiology, genomics, and ecology, as well as epithelial biology and immunology. Here, we have highlighted examples from recent CF microbial pathogenesis literature of how the host nutritional environment, immune response, and microbe-microbe interactions can feedback onto each other, leading to diverse effects on lung disease pathogenesis in CF.

Attachment and antimicrobial susceptibility of bacterial associates of zooplanktonic copepod: Lesson for environmental safety

The present study emphasizes on the antimicrobial susceptibility of different bacterial strains isolated from the external body surface of a commonly found zooplanktonic copepod (Heliodiaptomus viduus, Gurney, 1916) inhabiting both in fresh and brackish water bodies of Midnapore (West and East) Districts, West Bengal, India. Out of 62 bacterial isolated strains, 38 isolates were identified as Gram-positive while the remaining 24 isolates were found to be Gram-negative. Antimicrobial properties of all those bacterial strains were determined by Vitek 2 compact system using minimum inhibitory concentration (MIC) values. All isolated bacterial strains had exhibited differential susceptibilities against some selected antibiotics. Field Emission Scanning Electron Microscope (FE-SEM) analysis revealed the considerable association of bacteria on the cuticular body parts of the studied zooplankton. The outcomes of the present research are expected to enable health professionals in identifying two major problems -1) bacterial association with zooplankton which is so far mostly considered as a novel source of food for fish in aquatic ecosystems. 2) Selection of antibiotics as treatment measure because of the pathogenic effects of zooplankton associated bacteria on human being. This unattended arena of research is also supposed to evoke a new dimension not only because of bacteria-zooplankton interactions but also on undertaking of judicious strategies to find out proper ways and means to make the surface water suitable for the utilization by the common peoples (minimising bacterial contamination) in the context of human health and environmental safety.

Role of the Multidrug Resistance Efflux Pump MexCD-OprJ in the Pseudomonas aeruginosa Quorum Sensing Response

Multidrug efflux pumps constitute a category of antibiotic resistance determinants that are a part of the core bacterial genomes. Given their conservation, it is conceivable that they present functions beyond the extrusion of antibiotics currently used for therapy. Pseudomonas aeruginosa stands as a relevant respiratory pathogen, with a high prevalence at hospitals and in cystic fibrosis patients. Part of its success relies on its low susceptibility to antibiotics and on the production of virulence factors, whose expression is regulated in several cases by quorum sensing (QS). We found that overexpression of the MexCD-OprJ multidrug efflux pump shuts down the P. aeruginosa QS response. Our results support that MexCD-OprJ extrudes kynurenine, a precursor of the alkyl-quinolone signal (AQS) molecules. Anthranilate and octanoate, also AQS precursors, do not seem to be extruded by MexCD-OprJ. Kynurenine extrusion is not sufficient to reduce the QS response in a mutant overexpressing this efflux pump. Impaired QS response is mainly due to the extrusion of 4-hydroxy-2-heptylquinoline (HHQ), the precursor of the Pseudomonas Quinolone Signal (PQS), leading to low PQS intracellular levels and reduced production of QS signal molecules. As the consequence, the expression of QS-regulated genes is impaired and the production of QS-regulated virulence factors strongly decreases in a MexCD-OprN P. aeruginosa overexpressing mutant. Previous work showed that MexEF-OprJ, another P. aeruginosa efflux pump, is also able of extruding kynurenine and HHQ. However, opposite to our findings, the QS defect in a MexEF-OprN overproducer is due to kynurenine extrusion. These results indicate that, although efflux pumps can share some substrates, the affinity for each of them can be different. Although the QS response is triggered by population density, information on additional elements able of modulating such response is still scarce. This is particularly important in the case of P. aeruginosa lung chronic infections, a situation in which QS-defective mutants are accumulated. If MexCD-OprJ overexpression alleviates the cost associated to triggering the QS response when un-needed, it could be possible that MexCD-OprJ antibiotic resistant overproducer strains might be selected even in the absence of antibiotic selective pressure, acting as antibiotic resistant cheaters in heterogeneous P. aeruginosa populations.

Mutational Evolution of Pseudomonas aeruginosa Resistance to Ribosome-Targeting Antibiotics

The present work examines the evolutionary trajectories of replicate Pseudomonas aeruginosa cultures in presence of the ribosome-targeting antibiotics tobramycin and tigecycline. It is known that large number of mutations across different genes - and therefore a large number of potential pathways - may be involved in resistance to any single antibiotic. Thus, evolution toward resistance might, to a large degree, rely on stochasticity, which might preclude the use of predictive strategies for fighting antibiotic resistance. However, the present results show that P. aeruginosa populations evolving in parallel in the presence of antibiotics (either tobramycin or tigecycline) follow a set of trajectories that present common elements. In addition, the pattern of resistance mutations involved include common elements for these two ribosome-targeting antimicrobials. This indicates that mutational evolution toward resistance (and perhaps other properties) is to a certain degree deterministic and, consequently, predictable. These findings are of interest, not just for P. aeruginosa, but in understanding the general rules involved in the evolution of antibiotic resistance also. In addition, the results indicate that bacteria can evolve toward higher levels of resistance to antibiotics against which they are considered to be intrinsically resistant, as tigecycline in the case of P. aeruginosa and that this may confer cross-resistance to other antibiotics of therapeutic value. Our results are particularly relevant in the case of patients under empiric treatment with tigecycline, which frequently suffer P. aeruginosa superinfections.

The Therapeutic Pipeline for Pseudomonas aeruginosa Infections

Pseudomonas aeruginosa is a Gram-negative opportunistic pathogen, designated by the World Health Organization as a critical priority for development of new therapeutics due to high levels of intrinsic and acquired antibiotic resistance. Other challenges include its versatility (it can persist in the environment and most strains are capable of causing disease in compromised hosts), robust efflux mechanisms that limit drug penetration, and the propensity to form antimicrobial-tolerant biofilms. Novel therapeutics in development to prevent or treat P. aeruginosa infections include vaccines, biologics such as antimicrobial peptides and therapeutic antibodies, virulence inhibitors, antimicrobials with novel targets, antibody-drug conjugates, resistance inhibitor-antibiotic or antibiotic-potentiator combinations, and bacteriophages or phage-derived lysins.

Identification of a Novel Polyamine Scaffold With Potent Efflux Pump Inhibition Activity Toward Multi-Drug Resistant Bacterial Pathogens

We have previously reported the use of combinatorial chemistry to identify broad-spectrum antibacterial agents. Herein, we extend our analysis of this technology toward the discovery of anti-resistance molecules, focusing on efflux pump inhibitors. Using high-throughput screening against multi-drug resistant Pseudomonas aeruginosa, we identified a polyamine scaffold that demonstrated strong efflux pump inhibition without possessing antibacterial effects. We determined that these molecules were most effective with an amine functionality at R1 and benzene functionalities at R2 and R3. From a library of 188 compounds, we studied the properties of 5 lead agents in detail, observing a fivefold to eightfold decrease in the 90% effective concentration of tetracycline, chloramphenicol, and aztreonam toward P. aeruginosa isolates. Additionally, we determined that our molecules were not only active toward P. aeruginosa, but toward Acinetobacter baumannii and Staphylococcus aureus as well. The specificity of our molecules to efflux pump inhibition was confirmed using ethidium bromide accumulation assays, and in studies with strains that displayed varying abilities in their efflux potential. When assessing off target effects we observed no disruption of bacterial membrane polarity, no general toxicity toward mammalian cells, and no inhibition of calcium channel activity in human kidney cells. Finally, combination treatment with our lead agents engendered a marked increase in the bactericidal capacity of tetracycline, and significantly decreased viability within P. aeruginosa biofilms. As such, we report a unique polyamine scaffold that has strong potential for the future development of novel and broadly active efflux pump inhibitors targeting multi-drug resistant bacterial infections.

Influence of Excipients on the Antimicrobial Activity of Tobramycin Against Pseudomonas aeruginosa Biofilms

PURPOSE

It is unknown if inactive pharmaceutical ingredients influence the activity of antibiotics they are co-formulated with. Recently it was found that materials acting as carbon nutrient sources for bacteria can promote bacterial dispersion from a biofilm and/or reverse the persister state of a subpopulation of bacteria within the biofilms. Both can make bacteria more susceptible to antibiotics. Thus, the aim was to identify potential excipients to improve antibiotic activity in Pseudomonas aeruginosa biofilms.

METHODS

We screened 190 potential excipients alone, and in combination with tobramycin sulfate against P. aeruginosa (strain PAO1) grown planktonically or as biofilms. After the excipient screening stage, we investigated the effect of 10 selected excipients against a more virulent strain (luminescent strain UCBPP-PA14). Temporal changes in luminescence, as an indicator of bacterial proliferation, and surviving colony forming units (CFUs) from the treated PA14 biofilms were quantified.

RESULTS

Forty-eight materials tested caused a reduction of PAO1 proliferation either alone or combined with tobramycin. L-alanine (p < 0.05), D-alanine (p > 0.05), and N-acetyl-D-glucosaminitol (p > 0.05) improved the activity of tobramycin measured by PA14 luminometry. Additionally, L-alanine and succinic acid significantly reduced the survival of PA14 biofilms (p < 0.05).

CONCLUSIONS

L-alanine, succinic acid, and N-acetyl-D-glucosaminitol may be useful as antibiotic adjuvants in future tobramycin anti-biofilm formulations.

Chemical Modification and Detoxification of the Pseudomonas aeruginosa Toxin 2-Heptyl-4-hydroxyquinoline N-Oxide by Environmental and Pathogenic Bacteria

2-Heptyl-4-hydroxyquinoline N-oxide (HQNO), a major secondary metabolite and virulence factor produced by the opportunistic pathogen Pseudomonas aeruginosa, acts as a potent inhibitor of respiratory electron transfer and thereby affects host cells as well as microorganisms. In this study, we demonstrate the previously unknown capability of environmental and pathogenic bacteria to transform and detoxify this compound. Strains of Arthrobacter and Rhodococcus spp. as well as Staphylococcus aureus introduced a hydroxyl group at C-3 of HQNO, whereas Mycobacterium abscessus, M. fortuitum, and M. smegmatis performed an O-methylation, forming 2-heptyl-1-methoxy-4-oxoquinoline as the initial metabolite. Bacillus spp. produced the glycosylated derivative 2-heptyl-1-(β-d-glucopyranosydyl)-4-oxoquinoline. Assaying the effects of these metabolites on cellular respiration and on quinol oxidase activity of membrane fractions revealed that their EC₅₀ values were up to 2 orders of magnitude higher than that of HQNO. Furthermore, cellular levels of reactive oxygen species were significantly lower in the presence of the metabolites than under the influence of HQNO. Therefore, the capacity to transform HQNO should lead to a competitive advantage against P. aeruginosa. Our findings contribute new insight into the metabolic diversity of bacteria and add another layer of complexity to the metabolic interactions which likely contribute to shaping polymicrobial communities comprising P. aeruginosa.

Detection of Pseudomonas aeruginosa Metabolite Pyocyanin in Water and Saliva by Employing the SERS Technique

Pyocyanin (PYO) is a metabolite specific for Pseudomonas aeruginosa. In the case of immunocompromised patients, it is currently considered a biomarker for life-threating Pseudomonas infections. In the frame of this study it is shown, that PYO can be detected in aqueous solution by employing surface-enhanced Raman spectroscopy (SERS) combined with a microfluidic platform. The achieved limit of detection is 0.5 μM. This is ~2 orders of magnitude below the concentration of PYO found in clinical samples. Furthermore, as proof of principle, the SERS detection of PYO in the saliva of three volunteers was also investigated. This body fluid can be collected in a non-invasive manner and is highly chemically complex, making the detection of the target molecule challenging. Nevertheless, PYO was successfully detected in two saliva samples down to 10 μM and in one sample at a concentration of 25 μM. This indicates that the molecules present in saliva do not inhibit the efficient adsorption of PYO on the surface of the employed SERS active substrates.

Bronchial Epithelial Cells from Cystic Fibrosis Patients Express a Specific Long Non-coding RNA Signature upon Pseudomonas aeruginosa Infection

Pseudomonas aeruginosa (Pa) is the leading cause of chronic lung infection in Cystic Fibrosis (CF) patients. It is well recognized that CF epithelial cells fail to develop an appropriate response to infection, allowing bacterial colonization and a chronic inflammatory response. Since long non-coding RNAs (lncRNAs), are known to play a key role in regulating mammalian innate immune response, we hypothesized that CF cells exposed to Pa could express a specific lncRNA signature responsible of the maladaptative CF response. We analyzed transcriptomic datasets to compare the expression profiles of lncRNAs in primary CF and non-CF epithelial cells infected with Pa at 0, 2, 4, and 6 h of infection. Our analysis identified temporal expression signatures of 25, 73, 15, and 26 lncRNA transcripts differentially expressed at 0, 2, 4, and 6 h post-infection respectively, between CF and non-CF cells. In addition, we identified profiles specific to CF and non-CF cells. The differential expression of two candidate lncRNAs were independently validated using real-time PCR. We identified a specific CF signature of lncRNA expression in a context of Pa infection that could potentially play a role in the maladaptive immune response of CF patients.

Bile signalling promotes chronic respiratory infections and antibiotic tolerance

Despite aggressive antimicrobial therapy, many respiratory pathogens persist in the lung, underpinning the chronic inflammation and eventual lung decline that are characteristic of respiratory disease. Recently, bile acid aspiration has emerged as a major comorbidity associated with a range of lung diseases, shaping the lung microbiome and promoting colonisation by Pseudomonas aeruginosa in Cystic Fibrosis (CF) patients. In order to uncover the molecular mechanism through which bile modulates the respiratory microbiome, a combination of global transcriptomic and phenotypic analyses of the P. aeruginosa response to bile was undertaken. Bile responsive pathways responsible for virulence, adaptive metabolism, and redox control were identified, with macrolide and polymyxin antibiotic tolerance increased significantly in the presence of bile. Bile acids, and chenodeoxycholic acid (CDCA) in particular, elicited chronic biofilm behaviour in P. aeruginosa, while induction of the pro-inflammatory cytokine Interleukin-6 (IL-6) in lung epithelial cells by CDCA was Farnesoid X Receptor (FXR) dependent. Microbiome analysis of paediatric CF sputum samples demonstrated increased colonisation by P. aeruginosa and other Proteobacterial pathogens in bile aspirating compared to non-aspirating patients. Together, these data suggest that bile acid signalling is a leading trigger for the development of chronic phenotypes underlying the pathophysiology of chronic respiratory disease.

Tryptophan catabolism in Pseudomonas aeruginosa and potential for inter-kingdom relationship

BACKGROUND

Pseudomonas aeruginosa (Pa) is a Gram-negative bacteria frequently involved in healthcare-associated pneumonia with poor clinical outcome. To face the announced post-antibiotic era due to increasing resistance and lack of new antibiotics, new treatment strategies have to be developed. Immunomodulation of the host response involved in outcome could be an alternative therapeutic target in Pa-induced lung infection. Kynurenines are metabolites resulting from tryptophan catabolism and are known for their immunomodulatory properties. Pa catabolizes tryptophan through the kynurenine pathway. Interestingly, many host cells also possess the kynurenine pathway, whose metabolites are known to control immune system homeostasis. Thus, bacterial metabolites may interfere with the host's immune response. However, the kynurenine pathway in Pa, including functional enzymes, types and amounts of secreted metabolites remains poorly known. Using liquid chromatography coupled to mass spectrometry and different strains of Pa, we determined types and levels of metabolites produced by Pa ex vivo in growth medium, and the relevance of this production in vivo in a murine model of acute lung injury.

RESULTS

Ex vivo, Pa secretes clinically relevant kynurenine levels (μM to mM). Pa also secretes kynurenic acid and 3-OH-kynurenine, suggesting that the bacteria possess both a functional kynurenine aminotransferase and kynurenine monooxygenase. The bacterial kynurenine pathway is the major pathway leading to anthranilate production both ex vivo and in vivo. In the absence of the anthranilate pathway, the kynurenine pathway leads to kynurenic acid production.

CONCLUSION

Pa produces and secretes several metabolites of the kynurenine pathway. Here, we demonstrate the existence of new metabolic pathways leading to synthesis of bioactive molecules, kynurenic acid and 3-OH-kynurenine in Pa. The kynurenine pathway in Pa is critical to produce anthranilate, a crucial precursor of some Pa virulence factors. Metabolites (anthranilate, kynurenine, kynurenic acid) are produced at sustained levels both ex vivo and in vivo leading to a possible immunomodulatory interplay between bacteria and host. These data may imply that pulmonary infection with bacteria highly expressing the kynurenine pathway enzymes could influence the equilibrium of the host's tryptophan metabolic pathway, known to be involved in the immune response to infection. Further studies are needed to explore the effects of these metabolic changes on the pathophysiology of Pa infection.