Pseudomonal infection in cystic fibrosis: the battle continues

Structure-Interaction Relationship of Polymyxins with Lung Surfactant

Multidrug-resistant Gram-negative bacteria present an urgent and formidable threat to the global public health. Polymyxins have emerged as a last-resort therapy against these 'superbugs'; however, their efficacy against pulmonary infection is poor. In this study, we integrated chemical biology and molecular dynamics simulations to examine how the alveolar lung surfactant significantly reduces polymyxin antibacterial activity. We discovered that lung surfactant is a phospholipid-based permeability barrier against polymyxins, compromising their efficacy against target bacteria. Next, we unraveled the structure-interaction relationship between polymyxins and lung surfactant, elucidating the thermodynamics that govern the penetration of polymyxins through this critical surfactant layer. Moreover, we developed a novel analog, FADDI-235, which exhibited potent activity against Gram-negative bacteria, both in the presence and absence of lung surfactant. These findings shed new light on the sequestration mechanism of lung surfactant on polymyxins and importantly pave the way for the rational design of new-generation lipopeptide antibiotics to effectively treat Gram-negative bacterial pneumonia.

Structural Insights into Pseudomonas aeruginosa Exotoxin A-Elongation Factor 2 Interactions: A Molecular Dynamics Study

Exotoxin A (ETA) is an extracellular secreted toxin and a single-chain polypeptide with A and B fragments that is produced by Pseudomonas aeruginosa. It catalyzes the ADP-ribosylation of a post-translationally modified histidine (diphthamide) on eukaryotic elongation factor 2 (eEF2), which results in the inactivation of the latter and the inhibition of protein biosynthesis. Studies show that the imidazole ring of diphthamide plays an important role in the ADP-ribosylation catalyzed by the toxin. In this work, we employ different in silico molecular dynamics (MD) simulation approaches to understand the role of diphthamide versus unmodified histidine in eEF2 on the interaction with ETA. Crystal structures of the eEF2-ETA complexes with three different ligands NAD⁺, ADP-ribose, and βTAD were selected and compared in the diphthamide and histidine containing systems. The study shows that NAD⁺ bound to ETA remains very stable in comparison with other ligands, enabling the transfer of ADP-ribose to the N3 atom of the diphthamide imidazole ring in eEF2 during ribosylation. We also show that unmodified histidine in eEF2 has a negative impact on ETA binding and is not a suitable target for the attachment of ADP-ribose. Analyzing of radius of gyration and COM distances for NAD⁺, βTAD, and ADP-ribose complexes revealed that unmodified His affects the structure and destabilizes the complex with all different ligands throughout the MD simulations.

Surfing motility is a complex adaptation dependent on the stringent stress response in Pseudomonas aeruginosa LESB58

Cystic fibrosis (CF) is a genetic disease that affects mucin-producing body organs such as the lungs. Characteristic of CF is the production of thick, viscous mucus, containing the glycoprotein mucin, that can lead to progressive airway obstruction. Recently, we demonstrated that the presence of mucin induced a rapid surface adaptation in motile bacteria termed surfing motility, which data presented here indicates is very different from swarming motility. Pseudomonas aeruginosa, the main colonizing pathogen in CF, employs several stress coping mechanisms to survive the highly viscous environment of the CF lung. We used motility-based assays and RNA-Seq to study the stringent stress response in the hypervirulent CF isolate LESB58 (Liverpool Epidemic Strain). Motility experiments revealed that an LESB58 stringent response mutant (ΔrelAΔspoT) was unable to surf. Transcriptional profiling of ΔrelAΔspoT mutant cells from surfing agar plates, when compared to wild-type cells from the surfing edge, revealed 2,584 dysregulated genes. Gene Ontology and KEGG enrichment analysis revealed effects of the stringent response on amino acid, nucleic acid and fatty acid metabolism, TCA cycle and glycolysis, type VI secretion, as well as chemotaxis, cell communication, iron transport, nitrogen metabolic processes and cyclic-di-GMP signalling. Screening of the ordered PA14 transposon library revealed 224 mutants unable to surf and very limited overlap with genes required for swarming. Mutants affecting surfing included two downstream effector genes of the stringent stress response, the copper regulator cueR and the quinolone synthase pqsH. Both the cueR and pqsH cloned genes complemented the surfing deficiency of ΔrelAΔspoT. Our study revealed insights into stringent stress dependency in LESB58 and showed that surfing motility is stringently-controlled via the expression of cueR and pqsH. Downstream factors of the stringent stress response are important to investigate in order to fully understand its ability to colonize and persist in the CF lung.

Phenotypical Characteristics of the Black Yeast Exophiala dermatitidis Are Affected by Pseudomonas aeruginosa in an Artificial Sputum Medium Mimicking Cystic Fibrosis-Like Conditions

Research into the cooperative pathogenicity of microbes in cystic fibrosis (CF) lungs is crucial for an understanding of the pathophysiology of infections and the development of novel treatment strategies. This study investigated the impact of the common CF-associated bacterial pathogen Pseudomonas aeruginosa on the black yeast Exophiala dermatitidis. It evaluated the planktonic growth, biofilm formation, morphology, and virulence of the fungus in the presence or absence of P. aeruginosa. It also determined the role of P. aeruginosa quorum-sensing (QS) molecules within these interactions, e.g., by using sterile culture filtrate and QS-deficient mutants. P. aeruginosa is known to inhibit the planktonic growth of E. dermatitidis. We found that fungal biofilm formation increased in the presence of P. aeruginosa after 24 h but is decreased significantly after 48 h. This effect was reversed when, instead of QS wild-type strains, ΔlasR, and ΔrhlR mutants were added to E. dermatitidis biofilm formation. The number and length of hyphae were substantially reduced when E. dermatitidis was co-cultivated with P. aeruginosa, but not when it was co-cultivated with the mutants. Experiments testing the virulence of E. dermatitidis in the greater wax moth Galleria mellonella showed a synergetic effect on larval killing when E. dermatitidis was injected together with P. aeruginosa culture filtrate. Survival rates were decreased when biofilm culture filtrate was added but not when planktonic culture filtrate was added. In summary, P. aeruginosa affects the growth, morphology, biofilm formation, and virulence of E. dermatitidis. N-acyl-L-homoserine lactone (AHL) QS molecules regulated factors that have been shown to contribute to the inhibition of the ability of E. dermatitidis to form filaments and biofilm.

Pseudomonas rhizoryzae sp. nov., isolated from rice

Two yellow-pigmented, Gram-stain-negative and rod-shaped bacterial strains, designated as RY24^T and ZYY160, were isolated from rice. Results of phylogenetic analysis based on 16S rRNA gene sequences showed that strains RY24^T and ZYY160 belonged to the genus Pseudomonas, and the 16S rRNA gene sequence similarity was 100 % The DNA homology between the two strains was 99.7 %. The 16S rRNA and rpoD gene sequences of the two strains showed highest similarity values to Pseudomonas oryzihabitans CGMCC 1.3392^T and Pseudomonas psychrotolerans DSM 15758^T (sharing 99.31 and 94.34 %, respectively). The major fatty acids of two strains were identified as summed feature 8 (C_18:1ω7c and/or C_18:1ω6c), C_16;0 and summed feature 3 (C_16:1ω7c and/or C_16:1ω6c), and the major respiratory quinone was identified as ubiquinone Q-9, which are typical chemotaxonomic features of members of the genus Pseudomonas. The genomic DNA G+C contents of strains RY24^T and ZYY160 were determined to be 64.25 and 64.21 mol%, respectively. The DNA-DNA relatedness and average nucleotide identity values between the two strains and their closely related type strains were below 36 and 90 %, which supported that RY24^T and ZYY160 represent a novel species in the genus Pseudomonas. Phylogenetic and chemotaxonomic evidence, together with phenotypic characteristics, showed that the two isolates constitute a novel species of the genus Pseudomonas. The type strain is RY24^T (JCM 33201^T=ACCC 61555^T), for which the name Pseudomonas rhizoryzae sp. nov. is proposed.

Bird feathers as potential sources of pathogenic microorganisms: a new look at old diseases

This article describes methods of treatment for avian zoonoses, modern antibiotic therapy and drug resistance of selected pathogens, which pose a threat to the population’s health. A tabular form has been used to present the current data from the European Union from 2011 to 2017 regarding human morbidity and mortality and the costs incurred by national health systems for the treatment of zoonoses occurring in humans and animals. Moreover, the paper includes descriptions of selected diseases, which indirectly affect birds. Scientists can obtain information regarding the occurrence of particular diseases, their aetiology, epidemiology, incubation period and symptoms caused by dangerous microorganisms and parasites. This information should be of particular interest for people who have frequent contact with birds, such as ornithologists, as well as veterinarians, farm staff, owners of accompanying animals and zoological workers. This paper presents a review used for identification and genetic characterization of bacterial strains isolated from a variety of environmental sources, e.g., bird feathers along with their practical application. We describe the bacterial, viral and fungal serotypes present on avian feathers after the slaughter process. This review also enables us to effectively identify several of the early stages of infectious diseases from heterogeneous avian research material.

Ligand Selectivity between the ADP-Ribosylating Toxins: An Inverse-Docking Study for Multitarget Drug Discovery

Bacterial adenosine 5'-diphosphate-ribosylating toxins are encoded by several human pathogens, such as Pseudomonas aeruginosa (exotoxin A (ETA)), Corynebacterium diphtheriae (diphtheria toxin (DT)), and Vibrio cholerae (cholix toxin (CT)). The toxins modify eukaryotic elongation factor 2, an essential human enzyme in protein synthesis, thereby causing cell death. Targeting external virulence factors, such as the above toxins, is a promising alternative for developing new antibiotics, while at the same time avoiding drug resistance. This study aims to establish a reliable computational methodology to find a "silver bullet" able to target all three toxins. Herein, we have undertaken a detailed analysis of the active sites of ETA, DT, and CT, followed by the determination of the most appropriate selection of the size of the docking sphere. Thereafter, we tested two different approaches for normalizing the docking scores and used these to verify the best target (toxin) for each ligand. The results indicate that the methodology is suitable for identifying selective as well as multitoxin inhibitors, further validating the robustness of inverse docking for target-fishing experiments.

ChIP-seq reveals the global regulator AlgR mediating cyclic di-GMP synthesis in Pseudomonas aeruginosa

AlgR is a key transcriptional regulator required for the expression of multiple virulence factors, including type IV pili and alginate in Pseudomonas aeruginosa. However, the regulon and molecular regulatory mechanism of AlgR have yet to be fully elucidated. Here, among 157 loci that were identified by a ChIP-seq assay, we characterized a gene, mucR, which encodes an enzyme that synthesizes the intracellular second messenger cyclic diguanylate (c-di-GMP). A ΔalgR strain produced lesser biofilm than did the wild-type strain, which is consistent with a phenotype controlled by c-di-GMP. AlgR positively regulates mucR via direct binding to its promoter. A ΔalgRΔmucR double mutant produced lesser biofilm than did the single ΔalgR mutant, demonstrating that c-di-GMP is a positive regulator of biofilm formation. AlgR controls the levels of c-di-GMP synthesis via direct regulation of mucR. In addition, the cognate sensor of AlgR, FimS/AlgZ, also plays an important role in P. aeruginosa virulence. Taken together, this study provides new insights into the AlgR regulon and reveals the involvement of c-di-GMP in the mechanism underlying AlgR regulation.

The PqsR and RhlR transcriptional regulators determine the level of Pseudomonas quinolone signal synthesis in Pseudomonas aeruginosa by producing two different pqsABCDE mRNA isoforms

Regulation of gene expression plays a key role in bacterial adaptability to changes in the environment. An integral part of this gene regulatory network is achieved via quorum sensing (QS) systems that coordinate bacterial responses under high cellular densities. In the nosocomial pathogen Pseudomonas aeruginosa, the 2-alkyl-4-quinolone (pqs) signaling pathway is crucial for bacterial survival under stressful conditions. Biosynthesis of the Pseudomonas quinolone signal (PQS) is dependent on the pqsABCDE operon, which is positively regulated by the LysR family regulator PqsR and repressed by the transcriptional regulator protein RhlR. However, the molecular mechanisms underlying this inhibition have remained elusive. Here, we demonstrate that not only PqsR but also RhlR activates transcription of pqsA. The latter uses an alternative transcriptional start site and induces expression of a longer transcript that forms a secondary structure in the 5' untranslated leader region. As a consequence, access of the ribosome to the Shine-Dalgarno sequence is restricted and translation efficiency reduced. We propose a model of a novel posttranscriptional regulation mechanism that fine-tunes PQS biosynthesis, thus highlighting the complexity of quorum sensing in P. aeruginosa.

Bioengineered lysozyme reduces bacterial burden and inflammation in a murine model of mucoid Pseudomonas aeruginosa lung infection

The spread of drug-resistant bacterial pathogens is a growing global concern and has prompted an effort to explore potential adjuvant and alternative therapies derived from nature's repertoire of bactericidal proteins and peptides. In humans, the airway surface liquid layer is a rich source of antibiotics, and lysozyme represents one of the most abundant and effective antimicrobial components of airway secretions. Human lysozyme is active against both Gram-positive and Gram-negative bacteria, acting through several mechanisms, including catalytic degradation of cell wall peptidoglycan and subsequent bacterial lysis. In the infected lung, however, lysozyme's dense cationic character can result in sequestration and inhibition by polyanions associated with airway inflammation. As a result, the efficacy of the native enzyme may be compromised in the infected and inflamed lung. To address this limitation, we previously constructed a charge-engineered variant of human lysozyme that was less prone to electrostatic-mediated inhibition in vitro. Here, we employ a murine model to show that this engineered enzyme is superior to wild-type human lysozyme as a treatment for mucoid Pseudomonas aeruginosa lung infections. The engineered enzyme effectively decreases the bacterial burden and reduces markers of inflammation and lung injury. Importantly, we found no evidence of acute toxicity or allergic hypersensitivity upon repeated administration of the engineered biotherapeutic. Thus, the charge-engineered lysozyme represents an interesting therapeutic candidate for P. aeruginosa lung infections.

Alginate lyase exhibits catalysis-independent biofilm dispersion and antibiotic synergy

More than 2 decades of study support the hypothesis that alginate lyases are promising therapeutic candidates for treating mucoid Pseudomonas aeruginosa infections. In particular, the enzymes' ability to degrade alginate, a key component of mucoid biofilm matrix, has been the presumed mechanism by which they disrupt biofilms and enhance antibiotic efficacy. The systematic studies reported here show that, in an in vitro model, alginate lyase dispersion of P. aeruginosa biofilms and enzyme synergy with tobramycin are completely decoupled from catalytic activity. In fact, equivalent antibiofilm effects can be achieved with bovine serum albumin or simple amino acids. These results provide new insights into potential mechanisms of alginate lyase therapeutic activity, and they should motivate a careful reexamination of the fundamental assumptions underlying interest in enzymatic biofilm dispersion.

Genetically engineered alginate lyase-PEG conjugates exhibit enhanced catalytic function and reduced immunoreactivity

Alginate lyase enzymes represent prospective biotherapeutic agents for treating bacterial infections, particularly in the cystic fibrosis airway. To effectively deimmunize one therapeutic candidate while maintaining high level catalytic proficiency, a combined genetic engineering-PEGylation strategy was implemented. Rationally designed, site-specific PEGylation variants were constructed by orthogonal maleimide-thiol coupling chemistry. In contrast to random PEGylation of the enzyme by NHS-ester mediated chemistry, controlled mono-PEGylation of A1-III alginate lyase produced a conjugate that maintained wild type levels of activity towards a model substrate. Significantly, the PEGylated variant exhibited enhanced solution phase kinetics with bacterial alginate, the ultimate therapeutic target. The immunoreactivity of the PEGylated enzyme was compared to a wild type control using in vitro binding studies with both enzyme-specific antibodies, from immunized New Zealand white rabbits, and a single chain antibody library, derived from a human volunteer. In both cases, the PEGylated enzyme was found to be substantially less immunoreactive. Underscoring the enzyme's potential for practical utility, >90% of adherent, mucoid, Pseudomonas aeruginosa biofilms were removed from abiotic surfaces following a one hour treatment with the PEGylated variant, whereas the wild type enzyme removed only 75% of biofilms in parallel studies. In aggregate, these results demonstrate that site-specific mono-PEGylation of genetically engineered A1-III alginate lyase yielded an enzyme with enhanced performance relative to therapeutically relevant metrics.

Impairment of phagocytosis of apoptotic cells and its role in chronic airway diseases

Phagocytosis of dying cells is a complex and dynamic process coordinated by the interaction of many surface molecules, adaptors, and chemotactic molecules, and it is controlled at multiple levels. This well regulated clearance process is of utmost importance for the development and homeostasis of organisms because defective or inefficient phagocytosis may contribute to human pathologies. In this review we discuss recent advances in the knowledge of the molecular interactions involved in recognition and clearance of apoptotic cells and how derangement of these processes can contribute to the pathogenesis of chronic airway diseases such as chronic obstructive pulmonary disease, cystic fibrosis and asthma. We will briefly consider how different types of macrophages are implicated in chronic airway diseases. Finally, we will address possible therapeutic strategies, such as the use of macrolide antibiotics and statins, for modulating apoptotic cell clearance.

Pseudomonas taeanensis sp. nov., isolated from a crude oil-contaminated seashore

A novel Gram-negative, aerobic, motile, short rod-shaped bacterium, designated MS-3T, was isolated from a crude oil-contaminated seashore in Taean, Korea. Strain MS-3T grew at 4–30 °C, at pH 6.0–9.5 and with 0–5 % NaCl and was oxidase- and catalase-positive. Phylogenetic analysis based on 16S rRNA gene sequences revealed that strain MS-3T was most similar to Pseudomonas marincola KMM 3042T (97.9 % 16S rRNA gene sequence similarity), P. cuatrocienegasensis 1NT (97.8 %), P. borbori R-20821T (97.3 %) and P. lundensis ATCC 49968T (97.1 %). Relatively low levels of DNA–DNA relatedness were found between strain MS-3T and P. cuatrocienegasensis LMG 24676T (57.2 %), P. borbori LMG 23199T (39.7 %), P. marincola KMM 3042T (32.2 %) and P. lundensis KACC 10832T (32.1 %), which support the classification of strain MS-3T within a novel species of the genus Pseudomonas. The G+C content of the genomic DNA of strain MS-3T was 57.6 mol% and the major isoprenoid quinone was Q-9. Strain MS-3T contained summed feature 3 (iso-C15 : 0 2-OH and/or C16 : 1 ω7c; 38.0 %), C16 : 0 (24.4 %), C18 : 1 ω7c (12.8 %), C12 : 0 (9.6 %) and C10 : 0 3-OH (4.9 %) as the major cellular fatty acids. On the basis of the phenotypic, genotypic and phylogenetic data, strain MS-3T represents a novel species of the genus Pseudomonas, for which the name Pseudomonas taeanensis sp. nov. is proposed. The type strain is MS-3T (=KCTC 22612T =KACC 14032T =JCM 16046T =NBRL 105641T).

Structural and antimicrobial properties of human pre-elafin/trappin-2 and derived peptides against Pseudomonas aeruginosa

Background

Pre-elafin/trappin-2 is a human innate defense molecule initially described as a potent inhibitor of neutrophil elastase. The full-length protein as well as the N-terminal "cementoin" and C-terminal "elafin" domains were also shown to possess broad antimicrobial activity, namely against the opportunistic pathogen P. aeruginosa. The mode of action of these peptides has, however, yet to be fully elucidated. Both domains of pre-elafin/trappin-2 are polycationic, but only the structure of the elafin domain is currently known. The aim of the present study was to determine the secondary structures of the cementoin domain and to characterize the antibacterial properties of these peptides against P. aeruginosa.

Results

We show here that the cementoin domain adopts an α-helical conformation both by circular dichroism and nuclear magnetic resonance analyses in the presence of membrane mimetics, a characteristic shared with a large number of linear polycationic antimicrobial peptides. However, pre-elafin/trappin-2 and its domains display only weak lytic properties, as assessed by scanning electron micrography, outer and inner membrane depolarization studies with P. aeruginosa and leakage of liposome-entrapped calcein. Confocal microscopy of fluorescein-labeled pre-elafin/trappin-2 suggests that this protein possesses the ability to translocate across membranes. This correlates with the finding that pre-elafin/trappin-2 and elafin bind to DNA in vitro and attenuate the expression of some P. aeruginosa virulence factors, namely the biofilm formation and the secretion of pyoverdine.

Conclusions

The N-terminal cementoin domain adopts α-helical secondary structures in a membrane mimetic environment, which is common in antimicrobial peptides. However, unlike numerous linear polycationic antimicrobial peptides, membrane disruption does not appear to be the main function of either cementoin, elafin or full-length pre-elafin/trappin-2 against P. aeruginosa. Our results rather suggest that pre-elafin/trappin-2 and elafin, but not cementoin, possess the ability to modulate the expression of some P.aeruginosa virulence factors, possibly through acting on intracellular targets.

Impairment of apoptotic cell engulfment by pyocyanin, a toxic metabolite of Pseudomonas aeruginosa

RATIONALE

Cystic fibrosis lung disease is characterized by accumulation of apoptotic neutrophils, indicating impaired clearance of dying cells. Pseudomonas aeruginosa, the principal microbial pathogen in cystic fibrosis, manipulates apoptosis induction via production of toxic metabolites. Whether these metabolites, particularly pyocyanin, can also modulate apoptotic cell engulfment is unknown.

OBJECTIVES

To assess the effects of pyocyanin on apoptotic cell engulfment by macrophages in vitro and in vivo and to investigate potential mechanisms of the observed effects.

METHODS

Human monocyte-derived macrophages were treated with pyocyanin before challenge with apoptotic neutrophils, apoptotic Jurkat cells, or latex beads, and phagocytosis was assessed by light microscopy and flow cytometry. Effects of pyocyanin production on apoptotic cell clearance in vivo were assessed in a murine model, comparing infection by wild-type or pyocyanin-deficient P. aeruginosa. Oxidant production was investigated using fluorescent probes and pharmacologic inhibition and Rho GTPase signaling by immunoblotting and inhibitor studies.

MEASUREMENTS AND MAIN RESULTS

Pyocyanin treatment impaired macrophage engulfment of apoptotic cells in vitro, without inducing significant macrophage apoptosis, whereas latex bead uptake was preserved. Macrophage ingestion of apoptotic cells was reduced and late apoptotic/necrotic cells were increased in mice infected with pyocyanin-producing P. aeruginosa compared with the pyocyanin-deficient strain. Inhibition of apoptotic cell uptake involved intracellular generation of reactive oxygen species (ROS) and effects on Rho GTPase signaling. Antioxidants or blockade of Rho signaling substantially restored apoptotic cell engulfment.

CONCLUSIONS

These studies demonstrate that P. aeruginosa can manipulate the inflammatory microenvironment through inhibition of apoptotic cell engulfment, and suggest potential strategies to limit pulmonary inflammation in cystic fibrosis.

Inhibition of the Bacterial Heme Oxygenases from Pseudomonas aeruginosa and Neisseria meningitidis: Novel Antimicrobial Targets

The final step in heme utilization and iron acquisition in many pathogens is the oxidative cleavage of heme by heme oxygenase (HO), yielding iron, biliverdin, and carbon monoxide. Thus, the essential requirement for iron suggests that HO may provide a potential therapeutic target for antimicrobial drug development. Computer-aided drug design (CADD) combined with experimental assays identified small-molecule inhibitors of the Neisseria meningitidis HO (nm-HO). CADD virtual screening applied to 800 000 compounds identified 153 for biological assay. Several of the compounds were shown to have KD values in the micromolar range for nm-HO and the Pseudomonas aeruginosa HO (pa-HO). The compounds also inhibited the growth of P. aeruginosa as well as biliverdin formation in E. coli cells overexpressing nm-HO. Thus, CADD combined with experimental analysis has been used to identify novel inhibitors of the bacterial heme oxygenases that can cross the cell membrane and specifically inhibit HO activity.

The mechanism of heme transfer from the cytoplasmic heme binding protein PhuS to the delta-regioselective heme oxygenase of Pseudomonas aeruginosa

The opportunistic pathogen Pseudomonas aeruginosa has evolved two outer membrane receptor-mediated uptake systems (encoded by the phu and has operons) by which it can utilize the hosts heme and hemeproteins as a source of iron. PhuS is a cytoplasmic heme binding protein encoded within the phu operon and has previously been shown to function in the trafficking of heme to the iron-regulated heme oxygenase (pa-HO). While the heme association rate for PhuS was similar to that of myoglobin, a markedly higher rate of heme dissociation (approximately 10(5) s(-1)) was observed, in keeping with a function in heme-trafficking. Additionally, the transfer of heme from PhuS to pa-HO was shown to be specific and unidirectional when compared to transfer to the non-iron regulated heme oxygenase (BphO), in which heme distribution between the two proteins merely reflects their relative intrinsic affinities for heme. Furthermore, the rate of transfer of heme from holo-PhuS to pa-HO of 0.11 +/- 0.01 s(-1) is 30-fold faster than that to apo-myoglobin, despite the significant higher binding affinity of apo-myoglobin for heme (kH = 1.3 x 10(-8) microM) than that of PhuS (0.2 microM). This data suggests that heme transfer to pa-HO is independent of heme affinity and is consistent with temperature dependence studies which indicate the reaction is driven by a negative entropic contribution, typical of an ordered transition state, and supports the notion that heme transfer from PhuS to pa-HO is mediated via a specific protein-protein interaction. In addition, pH studies, and reactions conducted in the presence of cyanide, suggest the involvement of spin transition during the heme transfer process, whereby the heme undergoes spin change from 6-c LS to 6-c HS either in PhuS or pa-HO. On the basis of the magnitudes of the activation parameters obtained in the presence of cyanide, whereby both complexes are maintained in a 6-c LS state, and the biphasic kinetics of heme transfer from holo-PhuS to pa-HO-wt, supports the notion that the spin-state crossover occur within holo-PhuS prior to the heme transfer step. Alternatively, the lack of the biphasic kinetic with pa-HO-G125V, 6-c LS, and with comparable rate of heme transfer as pa-HO is supportive of a mechanism in which the spin-change could occur within pa-HO. The present data suggests either or both of the two pathways proposed for heme transfer may occur under the present experimental conditions. The dissection of which pathway is physiologically relevant is the focus of ongoing studies.

Mechanism of enhanced activity of liposome-entrapped aminoglycosides against resistant strains of Pseudomonas aeruginosa

Pseudomonas aeruginosa is inherently resistant to most conventional antibiotics. The mechanism of resistance of this bacterium is mainly associated with the low permeability of its outer membrane to these agents. We sought to assess the bactericidal efficacy of liposome-entrapped aminoglycosides against resistant clinical strains of P. aeruginosa and to define the mechanism of liposome-bacterium interactions. Aminoglycosides were incorporated into liposomes, and the bactericidal efficacies of both free and liposomal drugs were evaluated. To define the mechanism of liposome-bacterium interactions, transmission electron microscopy (TEM), flow cytometry, lipid mixing assay, and immunocytochemistry were employed. Encapsulation of aminoglycosides into liposomes significantly increased their antibacterial activity against the resistant strains used in this study (MICs of > or =32 versus < or =8 microg/ml). TEM observations showed that liposomes interact intimately with the outer membrane of P. aeruginosa, leading to the membrane deformation. The flow cytometry and lipid mixing assays confirmed liposome-bacterial membrane fusion, which increased as a function of incubation time. The maximum fusion rate was 54.3% +/- 1.5% for an antibiotic-sensitive strain of P. aeruginosa and 57.8% +/- 1.9% for a drug-resistant strain. The fusion between liposomes and P. aeruginosa significantly enhanced the antibiotics' penetration into the bacterial cells (3.2 +/- 2.3 versus 24.2 +/- 6.2 gold particles/bacterium, P < or = 0.001). Our data suggest that liposome-entrapped antibiotics could successfully resolve infections caused by antibiotic-resistant P. aeruginosa through an enhanced mechanism of drug entry into the bacterial cells.

Comparison of biophysical and biologic properties of alpha-helical enantiomeric antimicrobial peptides

In our previous study (Chen et al. J Biol Chem 2005, 280:12316-12329), we utilized an alpha-helical antimicrobial peptide V(681) as the framework to study the effects of peptide hydrophobicity, amphipathicity, and helicity on biologic activities where we obtained several V(681) analogs with dramatic improvement in peptide therapeutic indices against gram-negative and gram-positive bacteria. In the present study, the D-enantiomers of three peptides--V(681), V13A(D) and V13K(L) were synthesized to compare biophysical and biologic properties with their enantiomeric isomers. Each D-enantiomer was shown by circular dichroism spectroscopy to be a mirror image of the corresponding L-isomer in benign conditions and in the presence of 50% trifluoroethanol. L- and D-enantiomers exhibited equivalent antimicrobial activities against a diverse group of Pseudomonas aeruginosa clinical isolates, various gram-negative and gram-positive bacteria and a fungus. In addition, L- and D-enantiomeric peptides were equally active in their ability to lyse human red blood cells. The similar activity of L- and D-enantiomeric peptides on prokaryotic or eukaryotic cell membranes suggests that there are no chiral receptors and the cell membrane is the sole target for these peptides. Peptide D-V13K(D) showed significant improvements in the therapeutic indices compared with the parent peptide V(681) by 53-fold against P. aeruginosa strains, 80-fold against gram-negative bacteria, 69-fold against gram-positive bacteria, and 33-fold against Candida albicans. The excellent stability of D-enantiomers to trypsin digestion (no proteolysis by trypsin) compared with the rapid breakdown of the L-enantiomers highlights the advantage of the D-enantiomers and their potential as clinical therapeutics.

Multiple-locus variable number tandem repeats analysis for genetic fingerprinting of pathogenic bacteria

DNA fingerprinting has attracted considerable interest as means for identifying, tracing and preventing the dissemination of infectious agents. Various methods have been developed for typing of pathogenic bacteria, which differ in discriminative power, reproducibility and ease of interpretation. During recent years a typing method, which uses the information provided by whole genome sequencing of bacterial species, has gained increased attention. Short sequence repeat (SSR) motifs are known to undergo frequent variation in the number of repeated units through cellular mechanisms most commonly active during chromosome replication. A class of SSRs, named variable number of tandem repeats (VNTRs), has proven to be a suitable target for assessing genetic polymorphisms within bacterial species. This review attempts to give an overview of bacterial agents where VNTR-based typing, or multiple-locus variant-repeat analysis (MLVA) has been developed for typing purposes, together with addressing advantages and drawbacks associated with the use of tandem repeated DNA motifs as targets for bacterial typing and identification.