Post-secretional activation of Protease IV by quorum sensing in Pseudomonas aeruginosa

Multifaceted strategies for alleviating Pseudomonas aeruginosa infection by targeting protease activity: Natural and synthetic molecules

Pseudomonas aeruginosa has become a top-priority pathogen in the health sector because it is ubiquitous, has high metabolic/genetic versatility, and is identified as an opportunistic pathogen. The production of numerous virulence factors by P. aeruginosa was reported to act individually or cooperatively to make them robots invasion, adherences, persistence, proliferation, and protection against host immune systems. P. aeruginosa produces various kinds of extracellular proteases such as alkaline protease, protease IV, elastase A, elastase B, large protease A, Pseudomonas small protease, P. aeruginosa aminopeptidase, and MucD. These proteases effectively allow the cells to invade and destroy host cells. Thus, inhibiting these protease activities has been recognized as a promising approach to controlling the infection caused by P. aeruginosa. The present review discussed in detail the characteristics of these proteases and their role in infection to the host system. The second part of the review discussed the recent updates on the multiple strategies for attenuating or inhibiting protease activity. These strategies include the application of natural and synthetic molecules, as well as metallic/polymeric nanomaterials. It has also been reported that a propeptide present in the middle domain of protease IV also attenuates the virulence properties and infection ability of P. aeruginosa.

Bacterial-responsive biodegradable silver nanoclusters composite hydrogel for infected wound therapy

Skin wounds are susceptible to bacterial infections, which hinder healing and extend recovery. Herein, we designed a silver nanoclusters (Ag NCs) composite hydrogel for infected wound treatment via bacterial enzymatic degradation and Ag release. Using biocompatible gelatine and polyethylene glycol as the main components, DNA-templated Ag NCs were covalently linked to a polymer network to obtain the final nanocomposite hydrogel. This hydrogel exhibited good compressive and tensile stiffness, bioadhesion and water absorption. The overexpressed bacterial enzymes protease and DNase in the infected wound were hydrolysed by the gel matrix, subsequently releasing antibacterial Ag ions. In vitro experimental results proved that the hydrogel demonstrated excellent bactericidal effect on Staphylococcus aureus and Escherichia coli, which are commonly implicated in clinical wound infections. Animal experiments revealed that the hydrogel considerably promoted cell proliferation and wound healing with less inflammatory responses. Thus, these results demonstrate strategies for bacterial enzyme-responsive Ag release for infected wound healing, facilitating further development of intelligent bandages.

Dual inhibitors of Pseudomonas aeruginosa virulence factors LecA and LasB

Dual inhibitors of two key virulence factors of Pseudomonas aeruginosa, the lectin LecA and the protease LasB, open up an opportunity in the current antimicrobial-resistance crisis. A molecular hybridization approach enabled the discovery of potent, selective, and non-toxic thiol-based inhibitors, which simultaneously inhibit these two major extracellular virulence factors and therefore synergistically interfere with virulence. We further demonstrated that the dimerization of these monovalent dual inhibitors under physiological conditions affords divalent inhibitors of LecA with a 200-fold increase in binding affinity. The bifunctional LecA/LasB-blocker 12 showed superiority for the inhibition of virulence mediated by both targets over the individual inhibitors or combinations thereof in vitro. Our study sets the stage for a systematic exploration of dual inhibitors as pathoblockers for a more effective treatment of P. aeruginosa infections and the concept can certainly be extended to other targets and pathogens.

The Secreted Aminopeptidase of Pseudomonas aeruginosa (PaAP)

Pseudomonas aeruginosa is an opportunistic pathogen that causes severe infections in compromised hosts. P. aeruginosa infections are difficult to treat because of the inherent ability of the bacteria to develop antibiotic resistance, secrete a variety of virulence factors, and form biofilms. The secreted aminopeptidase (PaAP) is an emerging virulence factor, key in providing essential low molecular weight nutrients and a cardinal modulator of biofilm development. PaAP is therefore a new potential target for therapy of P. aeruginosa infections. The present review summarizes the current knowledge of PaAP, with special emphasis on its biochemical and enzymatic properties, activation mechanism, biological roles, regulation, and structure. Recently developed specific inhibitors and their potential as adjuncts in the treatment of P. aeruginosa infections are also described.

LasR regulates protease IV expression at suboptimal growth temperatures in Pseudomonas aeruginosa

The opportunistic pathogen Pseudomonas aeruginosa causes debilitating lung infections in people with cystic fibrosis, as well as eye, burn, and wound infections in otherwise immunocompetent individuals. Many of P. aeruginosa's virulence factors are regulated by environmental changes associated with human infection, such as a change in temperature from ambient to human body temperature. One such virulence factor is protease IV (PIV). Interestingly, piv expression is higher at ambient temperatures (22-28°C) compared to human body temperature (37°C). We found that piv expression was thermoregulated at stationary phase, but not exponential phase, and that piv is thermoregulated at the level of transcription. Protein levels of known transcriptional regulators of piv, the quorum sensing regulator LasR and the gene-silencing histone nucleoid silencing proteins MvaT/MvaU, were not thermoregulated. Using a transcriptional reporter for piv, we show that LasR activates piv expression at stationary phase at 25°C but not 37°C, while MvaT/MvaU are not required for piv thermoregulation. We also identified a las box in the piv promoter, which is important for piv thermoregulation. We propose that LasR directly regulates piv at stationary phase at 25°C but has a negligible impact at 37°C. Here, we show that piv is uniquely regulated by LasR in a temperature-dependent manner. Our findings suggest that the LasRI quorum sensing regulon of P. aeruginosa may not be fully characterized and that growth at non-standard laboratory conditions such as lower temperatures could reveal previously unrecognized quorum sensing regulated genes.

Zwitterion‐conjugated Topological Glycomimics for Dual‐Blocking Effects to Eradicate Biofilm Infection

P. aeruginosa, a leading nosocomial pathogen, commonly causes chronic biofilm infections in tissues and biomedical devices, including wound infections, osteomyelitis, and infective endocarditis, heavily threatening life. The dynamic lifecycle of these biofilms leads to persistent generation, making it challenging to prevent and disperse these biofilms effectively. Herein, a topological eight‐arm zwitterion‐conjugated glycomimetics (PCBAA‐b‐PLAMA)8 to address this challenge by exerting a dual‐blocking effect on P. aeruginosa biofilms is introduced. Initially, carboxybetaine acrylate (CBAA) and 2‐lactobionamidoethyl methacrylate (LAMA) are introduced to the topological bromine‐based initiator to prepare (PCBAA‐b‐PLAMA)8. This copolymer demonstrats remarkable efficiency in dispersing P. aeruginosa biofilms, approximately up to 99%. This high efficacy can be attributed to the multivalent and triaxial interactions between LAMA and CBAA groups, which enable the capture of P. aeruginosa cells and the biofilm matrix. Furthermore, (PCBAA‐b‐PLAMA)8 efficiently inhibit the expression of resistance genes related to biofilm formation and antibiotic efflux, including cdrA, lasB, mexE, and mexH, regaining bacterial cell sensitivity to antibiotics and further facilitating the natural dispersal of biofilms. This study provides a generic dual‐blocking strategy for the efficient eliminating of biofilms from biomedical devices.

Pseudomonas aeruginosa: pathogenesis, virulence factors, antibiotic resistance, interaction with host, technology advances and emerging therapeutics

Pseudomonas aeruginosa (P. aeruginosa) is a Gram-negative opportunistic pathogen that infects patients with cystic fibrosis, burn wounds, immunodeficiency, chronic obstructive pulmonary disorder (COPD), cancer, and severe infection requiring ventilation, such as COVID-19. P. aeruginosa is also a widely-used model bacterium for all biological areas. In addition to continued, intense efforts in understanding bacterial pathogenesis of P. aeruginosa including virulence factors (LPS, quorum sensing, two-component systems, 6 type secretion systems, outer membrane vesicles (OMVs), CRISPR-Cas and their regulation), rapid progress has been made in further studying host-pathogen interaction, particularly host immune networks involving autophagy, inflammasome, non-coding RNAs, cGAS, etc. Furthermore, numerous technologic advances, such as bioinformatics, metabolomics, scRNA-seq, nanoparticles, drug screening, and phage therapy, have been used to improve our understanding of P. aeruginosa pathogenesis and host defense. Nevertheless, much remains to be uncovered about interactions between P. aeruginosa and host immune responses, including mechanisms of drug resistance by known or unannotated bacterial virulence factors as well as mammalian cell signaling pathways. The widespread use of antibiotics and the slow development of effective antimicrobials present daunting challenges and necessitate new theoretical and practical platforms to screen and develop mechanism-tested novel drugs to treat intractable infections, especially those caused by multi-drug resistance strains. Benefited from has advancing in research tools and technology, dissecting this pathogen's feature has entered into molecular and mechanistic details as well as dynamic and holistic views. Herein, we comprehensively review the progress and discuss the current status of P. aeruginosa biophysical traits, behaviors, virulence factors, invasive regulators, and host defense patterns against its infection, which point out new directions for future investigation and add to the design of novel and/or alternative therapeutics to combat this clinically significant pathogen.

Potential Therapeutic Targets for Combination Antibody Therapy against Pseudomonas aeruginosa Infections

Despite advances in antimicrobial therapy and even the advent of some effective vaccines, Pseudomonas aeruginosa (P. aeruginosa) remains a significant cause of infectious disease, primarily due to antibiotic resistance. Although P. aeruginosa is commonly treatable with readily available therapeutics, these therapies are not always efficacious, particularly for certain classes of patients (e.g., cystic fibrosis (CF)) and for drug-resistant strains. Multi-drug resistant P. aeruginosa infections are listed on both the CDC’s and WHO’s list of serious worldwide threats. This increasing emergence of drug resistance and prevalence of P. aeruginosa highlights the need to identify new therapeutic strategies. Combinations of monoclonal antibodies against different targets and epitopes have demonstrated synergistic efficacy with each other as well as in combination with antimicrobial agents typically used to treat these infections. Such a strategy has reduced the ability of infectious agents to develop resistance. This manuscript details the development of potential therapeutic targets for polyclonal antibody therapies to combat the emergence of multidrug-resistant P. aeruginosa infections. In particular, potential drug targets for combinational immunotherapy against P. aeruginosa are identified to combat current and future drug resistance.

Alleviation of Pseudomonas aeruginosa Infection by Propeptide-Mediated Inhibition of Protease IV

Pseudomonas aeruginosa, an opportunistic human pathogen, expresses protease IV (PIV) for infection. Since the PIV activity can be inhibited by its propeptide, we tried to alleviate the severity of P. aeruginosa infection using the purified PIV propeptide (PIV_pp). The PIV_pp treatment of P. aeruginosa could significantly inhibit the PIV activity and reduce the virulence of P. aeruginosa in multiple invertebrate infection models, such as nematodes, brine shrimp, and mealworms. The effectiveness of PIV_pp was further confirmed using mouse skin infection and acute/chronic lung infection models. The amount of PIV_pp that inhibited the PIV activity of P. aeruginosa by 65% could alleviate the severity of infection significantly in all of the skin and acute/chronic lung infections. In addition, the PIV_pp treatment of P. aeruginosa facilitated the healing of the skin wound infections and repressed the growth of P. aeruginosa in the infected lung. The PIV_pp itself did not cause the induction of inflammatory cytokines or have any harmful effects on host tissues and did not affect bacterial growth. Taken together, P. aeruginosa infections can be alleviated by PIV_pp treatment. IMPORTANCE Pseudomonas aeruginosa is a highly antibiotic-resistant pathogen and is extremely difficult to treat. Instead of using conventional antibiotics, we attempted to alleviate P. aeruginosa infection using factors that P. aeruginosa itself produces naturally. Extracellular proteases are powerful virulence factors and important targets to control the P. aeruginosa infections. Propeptides are originally expressed as part of extracellular proteases, inhibiting their activity until they go out of the cell, preventing them from becoming toxic to the cells themselves. We confirmed, from multiple animal experiments, that treating P. aeruginosa with the purified propeptide can alleviate its infectivity. Propeptides specifically inhibit only their cognate protease without inhibiting other essential proteases of the host. The development of resistance can be avoided because the propeptide-mediated inhibition is an inherent mechanism of P. aeruginosa; hence, it will be difficult for P. aeruginosa to alter this mechanism. Since propeptides do not affect bacterial growth, there is no selective pressure to develop resistant cells.

Polymicrobial Interactions in the Cystic Fibrosis Airway Microbiome Impact the Antimicrobial Susceptibility of Pseudomonas aeruginosa

Pseudomonas aeruginosa is one of the most dominant pathogens in cystic fibrosis (CF) airway disease and contributes to significant inflammation, airway damage, and poorer disease outcomes. The CF airway is now known to be host to a complex community of microorganisms, and polymicrobial interactions have been shown to play an important role in shaping P. aeruginosa pathogenicity and resistance. P. aeruginosa can cause chronic infections that once established are almost impossible to eradicate with antibiotics. CF patients that develop chronic P. aeruginosa infection have poorer lung function, higher morbidity, and a reduced life expectancy. P. aeruginosa adapts to the CF airway and quickly develops resistance to several antibiotics. A perplexing phenomenon is the disparity between in vitro antimicrobial sensitivity testing and clinical response. Considering the CF airway is host to a diverse community of microorganisms or 'microbiome' and that these microorganisms are known to interact, the antimicrobial resistance and progression of P. aeruginosa infection is likely influenced by these microbial relationships. This review combines the literature to date on interactions between P. aeruginosa and other airway microorganisms and the influence of these interactions on P. aeruginosa tolerance to antimicrobials.

Extracellular proteolytic activation of Pseudomonas aeruginosa aminopeptidase (PaAP) and insight into the role of its non-catalytic N-terminal domain

Pseudomonas aeruginosa secretes several endopeptidases, including elastase, alkaline proteinase (Apr), a lysine-specific endopeptidase (LysC), and an aminopeptidase (PaAP), all of which are important virulence factors. Activation of the endopeptidases requires removal of an inhibitory N-terminal propeptide. Activation of pro-PaAP, in contrast, requires C-terminal processing. The activating proteases of pro-PaAP and their cleavage site(s) have not yet been defined. Studying pro-PaAP processing in a wild type P. aeruginosa strain and strains lacking either elastase or both elastase and Apr, we detected three processing variants, each ~56 kDa in size (AP56). Activity assays and N- and C-terminal sequence analyses of these variants pointed at LysC as the principal activating protease, cleaving a Lys512-Ala513 peptide bond at the C-terminal end of pro-PaAP. Elastase and/or Apr are required for activation of LysC, suggesting both are indirectly involved in activation of PaAP. To shed light on the function(s) of the N-terminal domain of AP56, we purified recombinant AP56 and generated from it the 28 kDa catalytic domain (AP28). The kinetic constants (Km and Kcat) for hydrolysis of Leu-, Lys-, Arg- and Met-p-nitroanilide (pNA) derivatives by AP56 and AP28 were then determined. The catalytic coefficients (Kcat/Km) for hydrolysis of all four substrates by AP28 and AP56 were comparable, indicating that the non-catalytic domain is not involved in hydrolysis of small substrates. It may, however, regulate hydrolysis of natural peptides/proteins. Lys-pNA was hydrolyzed 2 to 3-fold more rapidly than Leu-pNA and ~8-fold faster than Arg- or Met-pNA, indicating that Lys-pNA was the preferred substrate.

Calprotectin-Mediated Zinc Chelation Inhibits Pseudomonas aeruginosa Protease Activity in Cystic Fibrosis Sputum

Pseudomonas aeruginosa induces pathways indicative of low zinc availability in the cystic fibrosis (CF) lung environment. To learn more about P. aeruginosa zinc access in CF, we grew P. aeruginosa strain PAO1 directly in expectorated CF sputum. The P. aeruginosa Zur transcriptional repressor controls the response to low intracellular zinc, and we used the NanoString methodology to monitor levels of Zur-regulated transcripts, including those encoding a zincophore system, a zinc importer, and paralogs of zinc containing proteins that do not require zinc for activity. Zur-controlled transcripts were induced in sputum-grown P. aeruginosa compared to those grown in control cultures but not if the sputum was amended with zinc. Amendment of sputum with ferrous iron did not reduce expression of Zur-regulated genes. A reporter fusion to a Zur-regulated promoter had variable activity in P. aeruginosa grown in sputum from different donors, and this variation inversely correlated with sputum zinc concentrations. Recombinant human calprotectin (CP), a divalent-metal binding protein released by neutrophils, was sufficient to induce a zinc starvation response in P. aeruginosa grown in laboratory medium or zinc-amended CF sputum, indicating that CP is functional in the sputum environment. Zinc metalloproteases comprise a large fraction of secreted zinc-binding P. aeruginosa proteins. Here, we show that recombinant CP inhibited both LasB-mediated casein degradation and LasA-mediated lysis of Staphylococcus aureus, which was reversible with added zinc. These studies reveal the potential for CP-mediated zinc chelation to posttranslationally inhibit zinc metalloprotease activity and thereby affect the protease-dependent physiology and/or virulence of P. aeruginosa in the CF lung environment. IMPORTANCE The factors that contribute to worse outcomes in individuals with cystic fibrosis (CF) with chronic Pseudomonas aeruginosa infections are not well understood. Therefore, there is a need to understand environmental factors within the CF airway that contribute to P. aeruginosa colonization and infection. We demonstrate that growing bacteria in CF sputum induces a zinc starvation response that inversely correlates with sputum zinc levels. Additionally, both calprotectin and a chemical zinc chelator inhibit the proteolytic activities of LasA and LasB proteases, suggesting that extracellular zinc chelators can influence proteolytic activity and thus P. aeruginosa virulence and nutrient acquisition in vivo.

LasR-deficient Pseudomonas aeruginosa variants increase airway epithelial mICAM-1 expression and enhance neutrophilic lung inflammation

Pseudomonas aeruginosa causes chronic airway infections, a major determinant of lung inflammation and damage in cystic fibrosis (CF). Loss-of-function lasR mutants commonly arise during chronic CF infections, are associated with accelerated lung function decline in CF patients and induce exaggerated neutrophilic inflammation in model systems. In this study, we investigated how lasR mutants modulate airway epithelial membrane bound ICAM-1 (mICAM-1), a surface adhesion molecule, and determined its impact on neutrophilic inflammation in vitro and in vivo. We demonstrated that LasR-deficient strains induce increased mICAM-1 levels in airway epithelial cells compared to wild-type strains, an effect attributable to the loss of mICAM-1 degradation by LasR-regulated proteases and associated with enhanced neutrophil adhesion. In a subacute airway infection model, we also observed that lasR mutant-infected mice displayed greater airway epithelial ICAM-1 expression and increased neutrophilic pulmonary inflammation. Our findings provide new insights into the intricate interplay between lasR mutants, LasR-regulated proteases and airway epithelial ICAM-1 expression, and reveal a new mechanism involved in the exaggerated inflammatory response induced by lasR mutants.

Pseudomonas aeruginosa elastase (LasB) as a therapeutic target

Why is P. aeruginosa LasB elastase an attractive target for antivirulence therapy and what is the state-of-the art in LasB inhibitor design and development?

Phenotypic Adaptation of Pseudomonas aeruginosa in the Presence of Siderophore-Antibiotic Conjugates during Epithelial Cell Infection

Iron acquisition pathways have often been considered to be gateways for the uptake of antibiotics into bacteria. Bacteria excrete chelators, called siderophores, to access iron. Antibiotic molecules can be covalently attached to siderophores for their transport into pathogens during the iron-uptake process. P. aeruginosa produces two siderophores and is also able to use many siderophores produced by other bacteria. We investigated the phenotypic plasticity of iron-uptake pathway expression in an epithelial cell infection assay in the presence of two different siderophore-antibiotic conjugates, one with a hydroxamate siderophore and the second with a tris-catechol. Proteomic and RT-qPCR approaches showed that P. aeruginosa was able to sense the presence of both compounds in its environment and adapt the expression of its iron uptake pathways to access iron via them. Moreover, the catechol-type siderophore-antibiotic was clearly more efficient in inducing the expression of its corresponding transporter than the hydroxamate compound when both were simultaneously present. In parallel, the expression of the proteins of the two iron uptake pathways using siderophores produced by P. aeruginosa was significantly repressed in the presence of both conjugates. Altogether, the data indicate that catechol-type siderophores are more promising vectors for antibiotic vectorization using a Trojan-horse strategy.

Iron facilitates the RetS-Gac-Rsm cascade to inversely regulate protease IV (piv) expression via the sigma factor PvdS in Pseudomonas aeruginosa

Pseudomonas aeruginosa produces several proteases, such as an elastase (LasB protease), a LasA protease, and protease IV (PIV), which are thought as significant virulence factors during infection. Regulators of LasA and LasB expression have been identified and well characterized; however, the molecular details of this regulation of protease IV (PIV) remained largely unknown. Here, we describe the interaction between protease IV and the RetS/Rsm signalling pathway, which plays a central role in controlling the production of multiple virulence factors and the switch from planktonic to biofilm lifestyle. We show that the expression of piv was reduced in ΔretS or ΔrsmA strain grown under restrictive conditions but was induced in ΔretS or ΔrsmA mutant grown under rich conditions as compared with wild-type parent. We compare the expression of piv under various conditions and found that iron facilitates RetS/Rsm system to lead this inverse regulation. Moreover, we reveal that the RetS/Rsm pathway regulates PIV production dependent on the alternative sigma factor PvdS. Collectively, this study extends the understanding of the RetS/Rsm regulatory cascade in response to environmental signals and provides insights into how P. aeruginosa adapts to the complex conditions.

Pseudomonas aeruginosa Leucine Aminopeptidase Influences Early Biofilm Composition and Structure via Vesicle-Associated Antibiofilm Activity

Pseudomonas aeruginosa, known as one of the leading causes of disease in cystic fibrosis (CF) patients, secretes a variety of proteases. These enzymes contribute significantly to P. aeruginosa pathogenesis and biofilm formation in the chronic colonization of CF patient lungs, as well as playing a role in infections of the cornea, burn wounds, and chronic wounds. We previously characterized a secreted P. aeruginosa peptidase, PaAP, that is highly expressed in chronic CF isolates. This leucine aminopeptidase is highly expressed during infection and in biofilms, and it associates with bacterial outer membrane vesicles (OMVs), structures known to contribute to virulence mechanisms in a variety of Gram-negative species and one of the major components of the biofilm matrix. We hypothesized that PaAP may play a role in P. aeruginosa biofilm formation. Using a lung epithelial cell/bacterial biofilm coculture model, we show that PaAP deletion in a clinical P. aeruginosa background alters biofilm microcolony composition to increase cellular density, while decreasing matrix polysaccharide content, and that OMVs from PaAP-expressing strains but not PaAP alone or in combination with PaAP deletion strain-derived OMVs could complement this phenotype. We additionally found that OMVs from PaAP-expressing strains could cause protease-mediated biofilm detachment, leading to changes in matrix and colony composition. Finally, we showed that the OMVs could also mediate the detachment of biofilms formed by both nonself P. aeruginosa strains and Klebsiella pneumoniae, another respiratory pathogen. Our findings represent novel roles for OMVs and the aminopeptidase in the modulation of P. aeruginosa biofilm architecture.IMPORTANCE Biofilm formation by the bacterial pathogen P. aeruginosa is known to contribute to drug resistance in nosocomial infections and chronic lung infections of cystic fibrosis patients. In order to treat these infections more successfully, the mechanisms of bacterial biofilm development must be elucidated. While both bacterially secreted aminopeptidase and outer membrane vesicles have been shown to be abundant in P. aeruginosa biofilm matrices, the contributions of each of these factors to the steps in biofilm generation have not been well studied. This work provides new insight into how these bacterial components mediate the formation of a robust, drug-resistant extracellular matrix and implicates outer membrane vesicles as active components of biofilm architecture, expanding our overall understanding of P. aeruginosa biofilm biology.

Quorum sensing-dependent post-secretional activation of extracellular proteases in Pseudomonas aeruginosa

Pseudomonas aeruginosa secretes multiple proteases that are implicated in its pathogenesis, and most of them are regulated by quorum sensing (QS). In this study, we found that the activities of three major extracellular proteases, protease IV (PIV), elastase A (LasA), and elastase B (LasB), are reduced considerably when expressed in a QS mutant (MW1). PIV and LasA expressed in MW1 exhibited little activity, even when purified, and their activities were inhibited by noncleavage or binding of their propeptides. LasB was activated by a QS-dependent factor, indicating that, unlike what has been proposed previously, LasB is not autoactivated. When LasB was relieved from inhibition, it activated PIV, which then sequentially processed pro-LasA to mature LasA. When activated, LasB was not inhibited by exogenous addition of its propeptide, but LasA and PIV were inhibited by their propeptides, even after prior activation. These differences may be explained by the fact that LasB can degrade its own propeptide but PIV and LasA cannot. We also found that, although PIV is the preferred LasA-activating factor, LasB can also partially activate LasA. Overall, LasB, PIV, and LasA were activated postsecretionally in a cascading manner in which the initial activation of LasB was controlled tightly by QS at the protein level in addition to the well-known transcriptional control of these proteases by QS. Interestingly, human elastase also activated LasA, indicating that the activation cascade is triggered by host factors during infection. In summary, a QS-induced proteolytic cascade activates secreted proteases from P. aeruginosa.

Pseudomonas aeruginosa Keratitis: Protease IV and PASP as Corneal Virulence Mediators

Pseudomonas aeruginosa is a leading cause of bacterial keratitis, especially in users of contact lenses. These infections are characterized by extensive degradation of the corneal tissue mediated by Pseudomonas protease activities, including both Pseudomonas protease IV (PIV) and the P. aeruginosa small protease (PASP). The virulence role of PIV was determined by the reduced virulence of a PIV-deficient mutant relative to its parent strain and the mutant after genetic complementation (rescue). Additionally, the non-ocular pathogen Pseudomonas putida acquired corneal virulence when it produced active PIV from a plasmid-borne piv gene. The virulence of PIV is not limited to the mammalian cornea, as evidenced by its destruction of respiratory surfactant proteins and the cytokine interleukin-22 (IL-22), the key inducer of anti-bacterial peptides. Furthermore, PIV contributes to the P. aeruginosa infection of both insects and plants. A possible limitation of PIV is its inefficient digestion of collagens; however, PASP, in addition to cleaving multiple soluble proteins, is able to efficiently cleave collagens. A PASP-deficient mutant lacks the corneal virulence of its parent or rescue strain evidencing its contribution to corneal damage, especially epithelial erosion. Pseudomonas-secreted proteases contribute importantly to infections of the cornea, mammalian lung, insects, and plants.

Catabolism of Nucleic Acids by a Cystic Fibrosis Pseudomonas aeruginosa Isolate: An Adaptive Pathway to Cystic Fibrosis Sputum Environment

Pseudomonas aeruginosa is a major cause of morbidity and mortality in patients with cystic fibrosis (CF). We undertook Biolog Phenotype Microarray testing of P. aeruginosa CF isolates to investigate their catabolic capabilities compared to P. aeruginosa laboratory strains PAO1 and PA14. One strain, PASS4, displayed an unusual phenotype, only showing strong respiration on adenosine and inosine. Further testing indicated that PASS4 could grow on DNA as a sole carbon source, with a higher biomass production than PAO1. This suggested that PASS4 was specifically adapted to metabolize extracellular DNA, a substrate present at high concentrations in the CF lung. Transcriptomic and proteomic profiling of PASS4 and PAO1 when grown with DNA as a sole carbon source identified a set of upregulated genes, including virulence and host-adaptation genes. PASS4 was unable to utilize N-Acetyl-D-glucosamine, and when we selected PASS4 mutants able to grow on this carbon source, they also displayed a gain in ability to catabolize a broad range of other carbon sources. Genome sequencing of the mutants revealed they all contained mutations within the purK gene, encoding a key protein in the de novo purine biosynthesis pathway. This suggested that PASS4 was a purine auxotroph. Growth assays in the presence of 2 mM adenosine and the complementation of PASS4 with an intact purK gene confirmed this conclusion. Purine auxotrophy may represent a viable microbial strategy for adaptation to DNA-rich environments such as the CF lung.

Bacterial ornithine lipid, a surrogate membrane lipid under phosphate-limiting conditions, plays important roles in bacterial persistence and interaction with host

Ornithine lipids (OLs) are bacteria-specific lipids that are found in the outer membrane of Gram (-) bacteria and increase as surrogates of phospholipids under phosphate-limited environmental conditions. We investigated the effects of OL increase in bacterial membranes on pathogen virulence and the host immune response. In Pseudomonas aeruginosa, we increased OL levels in membranes by overexpressing the OL-synthesizing operon (olsBA). These increases changed the bacterial surface charge and hydrophobicity, which reduced bacterial susceptibility to antibiotics and antimicrobial peptides (AMPs), interfered with the binding of macrophages to bacterial cells and enhanced bacterial biofilm formation. When grown under low phosphate conditions, P. aeruginosa became more persistent in the treatment of antibiotics and AMPs in an olsBA-dependent manner. While OLs increased persistence, they attenuated P. aeruginosa virulence; in host cells, they reduced the production of inflammatory factors (iNOS, COX-2, PGE₂ and nitric oxide) and increased intracellular Ca²⁺ release. Exogenously added OL had similar effects on P. aeruginosa and host cells. Our results suggest that bacterial OL plays important roles in bacteria-host interaction in a way that enhances bacterial persistence and develops chronic adaptation to infection.

The potential of Loxosceles gaucho spider venom to regulate Pseudomonas aeruginosa mechanisms of virulence

Loxosceles venom is a potential source of bioactive molecules which may be transformed into antimicrobial products against multi-resistant bacteria. Here, it was investigated whether Loxosceles gaucho spider had any influence on the proliferation, enzyme release and biofilm formation of a Pseudomonas aeruginosa strain resistant to two different classes of antibiotic. The results demonstrated that L. gaucho whole venom has no influence on P. aeruginosa proliferation. However, it increases P. aeruginosa production of gelatinase, caseinase and biofilm formation. The same effects were noted when P. aeruginosa was exposed to a L. gaucho venom molecular fraction with mass lower than 1 kDa. Separation of this molecular fraction into different subsets by RP-HPLC demonstrated that, among the molecules with the ability to increase the production of enzymes and biofilm formation, there are some with antimicrobial activities whose effects are not observed in the whole venom. In summary, the results obtained herein indicate that L. gaucho venom has a variety of low molecular mass bioactive components that influence the mechanisms of virulence of P. aeruginosa in different ways.