ExoU expression by Pseudomonas aeruginosa correlates with acute cytotoxicity and epithelial injury

Differences in antimicrobial resistance between exoU and exoS isolates of Pseudomonas aeruginosa

PURPOSES

This study compared antimicrobial resistance between exoU and exoS Pseudomonas aeruginosa strains isolated from microbial keratitis (MK) and examined their resistance genotypes.

METHODS

The presence of exoU and exoS was determined in 187 MK isolates using PCR. Minimum inhibitory concentrations of ciprofloxacin, levofloxacin, gentamicin, and tobramycin were measured. Whole genome sequencing of 39 isolates was used to identify resistance genes via Resfinder. Mutations in key genes, including DNA gyrase, topoisomerase IV, efflux pumps, and DNA repair systems, were analyzed using Geneious Prime. Functional effects of novel SNPs were predicted using SIFT.

RESULTS

Antibiotic resistance was significantly higher in exoU than exoS: 38.2% vs. 20.5% for ciprofloxacin, 29.1% vs. 12.1% for levofloxacin, 40% vs. 23.5% for gentamicin, and 29.1% vs. 14.4% for tobramycin (all p < 0.05). ExoU isolates exclusively had mutations in GyrA (Thr83Ile) and ParC (Ser87Ile), as well as in efflux pump regulators MexZ (Gly89Ser), NalC (Asp79Glu) and MexS (Val73Ala) (p < 0.01). They also more frequently harbored the acquired resistance genes aph(6)-Id (55% vs. 0%) and aph(3'')-Ib (60% vs. 5.3%) and had higher mutation rates in DNA repair genes mutL (70% vs. 15.8%) and mutS (45% vs. 5.3%) (p < 0.01). Mutations in gyrA, parC, efflux pump (mexB, mexD, mexY) and regulator (mexZ, nalC, mexS) genes correlated with fluoroquinolone resistance (R ≥ 0.33; p ≤ 0.04). Possession of aph(3'')-Ib, aph(6)- Id and SNPs in efflux pump regulators mexZ and parR were associated with aminoglycoside resistance.

CONCLUSION

ExoU strains exhibited more resistance genes and mutations, contributing to higher resistance to fluoroquinolones and aminoglycosides.

The Interactive Dynamics of Pseudomonas aeruginosa in Global Ecology

Pseudomonas aeruginosa is an opportunistic bacterium widely distributed in both natural and urban environments, playing a crucial role in global microbial ecology. This article reviews the interactive dynamics of P. aeruginosa across different ecosystems, highlighting its capacity for adaptation and resistance in response to environmental and therapeutic pressures. We analyze the mechanisms of antibiotic resistance, including the presence of resistance genes and efflux systems, which contribute to its persistence in both clinical and nonclinical settings. The interconnection between human, animal, and environmental health, within the context of the One Health concept, is discussed, emphasizing the importance of monitoring and sustainable management practices to mitigate the spread of resistance. Through a holistic approach, this work offers insights into the influence of P. aeruginosa on public health and biodiversity.

Pseudomonas aeruginosa aggregates elicit neutrophil swarming

Pseudomonas aeruginosa, a gram-negative multidrug-resistant (MDR) opportunist, belongs to the ESKAPE group of pathogens associated with the highest risk of mortality. Neutrophil swarming is a host defense strategy triggered by larger threats, where neutrophil swarms contain and clear damage/infection. Current ex vivo models designed to study neutrophil-pathogen interactions largely focus on individual neutrophil engagement with bacteria and fail to capture neutrophil swarming. Here, we report an ex vivo model that reproducibly elicits neutrophil swarming in response to bacterial aggregates. A rapid and robust swarming response follows engagement with pathogenic targets. Components of the type III secretion system (T3SS), a critical P. aeruginosa virulence determinant, are involved in swarm interaction. This ex vivo approach for studying neutrophil swarming in response to large pathogen targets constitutes a valuable tool for elucidating host-pathogen interaction mechanisms and for evaluating novel therapeutics to combat MDR infections.

Cross-membrane cooperation among bacteria can facilitate intracellular pathogenesis

Pseudomonas aeruginosa is a Gram-negative opportunistic pathogen able to cause life- and sight-threating infections. Once considered an extracellular pathogen, numerous studies have shown it can survive intracellularly. Previously, we showed that P. aeruginosa inside cells can diversify into distinct subpopulations in vacuoles and the cytoplasm. Here, we report that the transition from vacuoles to cytoplasm requires collaboration with the extracellular subpopulation, through Ca2+ influx enabled by their type III secretion system (T3SS) translocon pore proteins. Moreover, we show that collaboration among P. aeruginosa subpopulations can contribute to disseminating intracellular bacteria in vivo in a mouse infection model. This study provides the basis for future studies to investigate how cooperation of extracellular and intracellular bacteria within the host may contribute to disease progression and persistence.

Urinary tract infections and catheter-associated urinary tract infections caused by Pseudomonas aeruginosa

SUMMARYUrinary tract infection (UTI) is one of the most common infections in otherwise healthy individuals. UTI is also common in healthcare settings where patients often require urinary catheters to alleviate urinary retention. The placement of a urinary catheter often leads to catheter-associated urinary tract infection (CAUTI) caused by a broad range of opportunistic pathogens, commonly referred to as ESKAPE (Enterococcus, Staphylococcus, Klebsiella, Acinetobacter, Pseudomonas, and Enterobacter) pathogens. Our understanding of CAUTI is complicated by the differences in pathogens, in initial microbial load, changes that occur due to the duration of catheterization, and the relationship between infection (colonization) and disease symptoms. To advance our understanding of CAUTI, we reviewed UTI and CAUTI caused by Pseudomonas aeruginosa which is unique in that it is not commonly found associated with human microbiomes. For this reason, the ability of P. aeruginosa to cause UTI and CAUTI requires the introduction of the bacteria to the bladder from catheterization. Once in the host, the virulence factors used by P. aeruginosa in these infections remain an area of ongoing research. In this review, we will discuss studies that focus on P. aeruginosa UTI and CAUTI to better understand the infection dynamics and outcome in clinical settings, virulence factors associated with P. aeruginosa isolated from the urinary tract, and animal studies to test which bacterial factors are required for this infection. Understanding how P. aeruginosa can cause UTI and CAUTI can provide an understanding of how these infections initiate and progress and may provide possible strategies to limit these infections.

Effects of the combination of anti-PcrV antibody and bacteriophage therapy in a mouse model of Pseudomonas aeruginosa pneumonia

Acute lung injury caused by Pseudomonas aeruginosa is attributed to the translocation of cytotoxin into pulmonary epithelial cells via the P. aeruginosa type III secretion system. This virulence can be blocked with a specific antibody against PcrV in this secretion system. However, because anti-PcrV antibodies do not have bactericidal activity, the treatment of bacteria depends on the phagocytic system of the host. In this study, we investigated the therapeutic effect of combination therapy with an anti-PcrV antibody and bactericidal bacteriophages on acute lung injury and subsequent death in mice compared with a single treatment. After the mice intratracheally received a lethal dose of the cytotoxic P. aeruginosa strain, a second instillation was performed with saline, anti-PcrV IgG, bacteriophages, or a mixture of anti-PcrV and bacteriophages. The survival rates 24 h after infection were as follows: 7.1% in the saline group, 26.7% in the anti-PcrV group, 41.2% in the phage group, and 66.7% in the anti-PcrV + phage group (P < 0.001 vs saline-treated group). The activity of surviving mice in the anti-PcrV + phage group was significantly greater than that in the saline group. The lung weight in the anti-PcrV + phage group was significantly lower than that in the anti-PcrV group. In conclusion, combination therapy with an anti-PcrV antibody and a bacteriophage reduces acute lung injury and suggests improved survival compared with each treatment alone. This combination therapy, which does not rely on conventional antibiotics, could constitute a new strategy for treating multidrug-resistant P. aeruginosa infections.IMPORTANCECombination therapy with either bacteriophages alone or in combination with anti-PcrV antibodies in a mouse model of Pseudomonas aeruginosa pneumonia may reduce the acute lung injury and improve survival. This combination therapy, which does not rely on conventional antibiotics, may be a new strategy to treat multidrug-resistant Pseudomonas aeruginosa infections.

The battle within: how Pseudomonas aeruginosa uses host-pathogen interactions to infect the human lung

Pseudomonas aeruginosa is a versatile Gram-negative pathogen known for its ability to invade the respiratory tract, particularly in cystic fibrosis patients. This review provides a comprehensive analysis of the multifaceted strategies for colonization, virulence, and immune evasion used by P. aeruginosa to infect the host. We explore the extensive protein arsenal of P. aeruginosa, including adhesins, exotoxins, secreted proteases, and type III and VI secretion effectors, detailing their roles in the infective process. We also address the unique challenge of treating diverse lung conditions that provide a natural niche for P. aeruginosa on the airway surface, with a particular focus in cystic fibrosis. The review also discusses the current limitations in treatment options due to antibiotic resistance and highlights promising future approaches that target host-pathogen protein-protein interactions. These approaches include the development of new antimicrobials, anti-attachment therapies, and quorum-sensing inhibition molecules. In summary, this review aims to provide a holistic understanding of the pathogenesis of P. aeruginosa in the respiratory system, offering insights into the underlying molecular mechanisms and potential therapeutic interventions.

Novel humanized anti-PcrV monoclonal antibody COT-143 protects mice from lethal Pseudomonas aeruginosa infection via inhibition of toxin translocation by the type III secretion system

Treatment of Pseudomonas aeruginosa infection is challenging due to its intrinsic and acquired antibiotic resistance. As the number of current therapeutic options for P. aeruginosa infections is limited, developing novel treatments against the pathogen is an urgent clinical priority. The suppression of virulence of P. aeruginosa could be a new therapeutic option, and the type III secretion system (T3SS), which enables the bacteria to translocate various kinds of toxins into host cells and inhibits cellular functions, is considered as one possible target. In this report, we examined T3SS inhibition by COT-143/INFEX702, a humanized monoclonal antibody against PcrV, T3SS component, and present the crystal structure of the antibody-PcrV complex. COT-143 inhibited T3SS-dependent cytotoxicity and protected mice from the mortality caused by P. aeruginosa infection. The inhibition of cytotoxicity coincided with inhibition of translocon formation in a host cell membrane, which is necessary for T3SS intoxication. COT-143 protected murine neutrophils and facilitated phagocytosis of P. aeruginosa. These results suggest that COT-143 facilitates P. aeruginosa clearance by protecting neutrophil via inhibition of T3SS-dependent toxin translocation. This is the first report to show that an anti-PcrV antibody directly interferes with translocon formation to inhibit intoxication of host cells.

The Role of Pseudomonas aeruginosa in the Pathogenesis of Corneal Ulcer, Its Associated Virulence Factors, and Suggested Novel Treatment Approaches

BACKGROUND

Pseudomonas aeruginosa (P. aeruginosa), is a diverse Gram-negative pathogen commonly associated with a wide spectrum of infections. It is indicated to be the most prevalent causative agent in the development of bacterial keratitis linked with the use of contact lens. Corneal infections attributed to P. aeruginosa frequently have poor clinical outcomes necessitating lengthy and costly therapies. Therefore, this review looks at the aetiology of P. aeruginosa bacterial keratitis as well as the bacterial drivers of its virulence and the potential therapeutics on the horizon.

METHOD

A literature review with the articles used for the review searched for and retrieved from PubMed, Scopus, and Google Scholar (date last accessed 1 April 2024). The keywords used for the search criteria were "Pseudomonas and keratitis, biofilm and cornea as well as P. aeruginosa".

RESULTS

P. aeruginosa is implicated in the pathogenesis of bacterial keratitis associated with contact lens usage. To reduce the potential seriousness of these infections, a variety of contact lens-cleaning options are available. However, continuous exposure to a range of antibiotics doses, from sub-inhibitory to inhibitory, has been shown to lead to the development of resistance to both antibiotics and disinfectant. Generally, there is a global public health concern regarding the rise of difficult-to-treat infections, particularly in the case of P. aeruginosa virulence in ocular infections. This study of the basic pathogenesis of a prevalent P. aeruginosa strain is therefore implicated in keratitis. To this effect, anti-virulence methods and phage therapy are being researched and developed in response to increasing antibiotic resistance.

CONCLUSION

This review has shown P. aeruginosa to be a significant cause of bacterial keratitis, particularly among users of contact lens. It also revealed treatment options, their advantages, and their drawbacks, including prospective candidates.

The quorum sensing regulator RhlR positively controls the expression of the type III secretion system in Pseudomonas aeruginosa PAO1

Pseudomonas aeruginosa is an opportunist bacterium that causes acute and chronic infections. During acute infections, the type III secretion system (T3SS) plays a pivotal role in allowing the bacteria to translocate effectors such as ExoS, ExoT, and ExoY into host cells for colonization. Previous research on the involvement of quorum sensing systems Las and Rhl in controlling the T3SS gene expression produced ambiguous results. In this study, we determined the role of the Las and Rhl systems and the PqsE protein on T3SS expression. Our results show that in the wild-type PAO1 strain, the deletion of lasR or pqsE do not affect the secretion of ExoS. However, rhlI inactivation increases the expression of T3SS genes. In contrast to the rhlI deletion, rhlR inactivation decreases both T3SS genes expression and ExoS secreted protein levels, and this phenotype is restored when this mutant is complemented with the exsA gene, which codes for the master regulator of the T3SS. Additionally, cytotoxicity is affected in the rhlR mutant strain compared with its PAO1 parental strain. Overall, our results indicate that neither the Las system nor PqsE are involved in regulating the T3SS. Moreover, the Rhl system components have opposite effects, RhlI participates in negatively controlling the T3SS expression, while RhlR does it in a positive way, and this regulation is independent of C4 or PqsE. Finally, we show that rhlR, rhlI, or pqsE inactivation abolished pyocyanin production in T3SS-induction conditions. The ability of RhlR to act as a positive T3SS regulator in the absence of its cognate autoinducer and PqsE shows that it is a versatile regulator that controls different virulence traits allowing P. aeruginosa to compete for a niche.

A Bispecific Monoclonal Antibody Targeting Psl and PcrV Enhances Neutrophil-Mediated Killing of Pseudomonas aeruginosa in Patients with Bronchiectasis

Rationale: Pseudomonas aeruginosa infection is associated with worse outcomes in bronchiectasis. Impaired neutrophil antimicrobial responses contribute to bacterial persistence. Gremubamab is a bivalent, bispecific monoclonal antibody targeting Psl exopolysaccharide and the type 3 secretion system component PcrV. Objectives: This study evaluated the efficacy of gremubamab to enhance killing of P. aeruginosa by neutrophils from patients with bronchiectasis and to prevent P. aeruginosa-associated cytotoxicity. Methods: P. aeruginosa isolates from a global bronchiectasis cohort (n = 100) underwent whole-genome sequencing to determine target prevalence. Functional activity of gremubamab against selected isolates was tested in vitro and in vivo. Patients with bronchiectasis (n = 11) and control subjects (n = 10) were enrolled, and the effect of gremubamab in peripheral blood neutrophil opsonophagocytic killing (OPK) assays against P. aeruginosa was evaluated. Serum antibody titers to Psl and PcrV were determined (n = 30; 19 chronic P. aeruginosa infection, 11 no known P. aeruginosa infection), as was the effect of gremubamab treatment in OPK and anti-cytotoxic activity assays. Measurements and Main Results: Psl and PcrV were conserved in isolates from chronically infected patients with bronchiectasis. Seventy-three of 100 isolates had a full psl locus, and 99 of 100 contained the pcrV gene, with 20 distinct full-length PcrV protein subtypes identified. PcrV subtypes were successfully bound by gremubamab and the monoclonal antibody-mediated potent protective activity against tested isolates. Gremubamab increased bronchiectasis patient neutrophil-mediated OPK (+34.6 ± 8.1%) and phagocytosis (+70.0 ± 48.8%), similar to effects observed in neutrophils from control subjects (OPK, +30.1 ± 7.6%). No evidence of competition between gremubamab and endogenous antibodies was found, with protection against P. aeruginosa-induced cytotoxicity and enhanced OPK demonstrated with and without addition of patient serum. Conclusions: Gremubamab enhanced bronchiectasis patient neutrophil phagocytosis and killing of P. aeruginosa and reduced virulence.

Evidence for intracellular Pseudomonas aeruginosa

Pseudomonas aeruginosa is a significant cause of global morbidity and mortality. Although it is often regarded as an extracellular pathogen toward human cells, numerous investigations report its ability to survive and replicate within host cells, and additional studies demonstrate specific mechanisms enabling it to adopt an intracellular lifestyle. This ability of P. aeruginosa remains less well-investigated than that of other intracellular bacteria, although it is currently gaining attention. If intracellular bacteria are not killed after entering host cells, they may instead receive protection from immune recognition and experience reduced exposure to antibiotic therapy, among additional potential advantages shared with other facultative intracellular pathogens. For this review, we compiled studies that observe intracellular P. aeruginosa across strains, cell types, and experimental systems in vitro, as well as contextualize these findings with the few studies that report similar observations in vivo. We also seek to address key findings that drove the perception that P. aeruginosa remains extracellular in order to reconcile what is currently understood about intracellular pathogenesis and highlight open questions regarding its contribution to disease.

Unveiling the ocular battlefield: Insights into Pseudomonas aeruginosa virulence factors and their implications for multidrug resistance

The research investigates the virulence factors of Pseudomonas aeruginosa (P. aeruginosa), a pathogen known for its ability to cause human infections by releasing various exoenzymes and virulence factors. Particularly relevant in ocular infections, where tissue degeneration can occur, even after bacterial growth has ceased due to the potential role of secreted proteins/enzymes. Clinical isolates of P. aeruginosa, both ocular (146) and non-ocular (54), were examined to determine the frequency and mechanism of virulence factors. Phenotypic characterization revealed the production of alginate, biofilm, phospholipase C, and alkaline protease, while genotypic testing using internal uniplex PCR identified the presence of Exo U, S, T, Y, and LasB genes. Results showed a significant prevalence of Exo U and Y genes in ocular isolates, a finding unique to Indian studies. Additionally, the study noted that ocular isolates often contained all four secretomes, suggesting a potential link between these factors and ocular infections. These findings contribute to understanding the pathogenesis of P. aeruginosa infections, particularly in ocular contexts, and highlights the importance of comprehensive virulence factor analysis in clinical settings.

Keratinocyte-derived small extracellular vesicles supply antigens for CD1a-resticted T cells and promote their type 2 bias in the context of filaggrin insufficiency

Introduction

Exosome-enriched small extracellular vesicles (sEVs) are nanosized organelles known to participate in long distance communication between cells, including in the skin. Atopic dermatitis (AD) is a chronic inflammatory skin disease for which filaggrin (FLG) gene mutations are the strongest genetic risk factor. Filaggrin insufficiency affects multiple cellular function, but it is unclear if sEV-mediated cellular communication originating from the affected keratinocytes is also altered, and if this influences peptide and lipid antigen presentation to T cells in the skin.

Methods

Available mRNA and protein expression datasets from filaggrin-insufficient keratinocytes (shFLG), organotypic models and AD skin were used for gene ontology analysis with FunRich tool. sEVs secreted by shFLG and control shC cells were isolated from conditioned media by differential centrifugation. Mass spectrometry was carried out for lipidomic and proteomic profiling of the cells and sEVs. T cell responses to protein, peptide, CD1a lipid antigens, as well as phospholipase A2-digested or intact sEVs were measured by ELISpot and ELISA.

Results

Data analysis revealed extensive remodeling of the sEV compartment in filaggrin insufficient keratinocytes, 3D models and the AD skin. Lipidomic profiles of shFLGsEV showed a reduction in the long chain (LCFAs) and polyunsaturated fatty acids (PUFAs; permissive CD1a ligands) and increased content of the bulky headgroup sphingolipids (non-permissive ligands). This resulted in a reduction of CD1a-mediated interferon-γ T cell responses to the lipids liberated from shFLG-generated sEVs in comparison to those induced by sEVs from control cells, and an increase in interleukin 13 secretion. The altered sEV lipidome reflected a generalized alteration in the cellular lipidome in filaggrin-insufficient cells and the skin of AD patients, resulting from a downregulation of key enzymes implicated in fatty acid elongation and desaturation, i.e., enzymes of the ACSL, ELOVL and FADS family.

Discussion

We determined that sEVs constitute a source of antigens suitable for CD1a-mediated presentation to T cells. Lipids enclosed within the sEVs secreted on the background of filaggrin insufficiency contribute to allergic inflammation by reducing type 1 responses and inducing a type 2 bias from CD1a-restricted T cells, thus likely perpetuating allergic inflammation in the skin.

Site-directed spin label EPR studies of the structure and membrane interactions of the bacterial phospholipase ExoU

Site-directed spin labeling (SDSL) has been invaluable in the analysis of protein structure and dynamics, and has been particularly useful in the study of membrane proteins. ExoU, an important virulence factor in Pseudomonas aeruginosa infections, is a bacterial phospholipase A2 that functions at the membrane - aqueous interface. Using SDSL methodology developed in the Hubbell lab, we find that the region surrounding the catalytic site of ExoU is buried within the tertiary structure of the protein in the soluble, apoenzyme state, but shows a significant increase in dynamics upon membrane binding and activation by ubiquitin. Continuous wave (CW) power saturation EPR studies show that the conserved serine hydrolase motif of ExoU localizes to the membrane surface in the active, holoenzyme state. SDSL studies on the C-terminal four-helix bundle (4HB) domain of ExoU similarly show a co-operative effect of ubiquitin binding and membrane association. CW power saturation studies of the 4HB domain indicate that two interhelical loops intercalate into the lipid bilayer upon formation of the holoenzyme state, anchoring ExoU at the membrane surface. Together these studies establish the orientation and localization of ExoU and the membrane surface, and illustrate the power of SDSL as applied to peripheral membrane proteins.

The type III secretion system facilitates systemic infections of Pseudomonas aeruginosa in the clinic

IMPORTANCE

The identification of decisive virulence-associated genes in highly pathogenic P. aeruginosa isolates in the clinic is essential for diagnosis and the start of appropriate treatment. Over the past decades, P. aeruginosa ST463 has spread rapidly in East China and is highly resistant to β-lactams. Given the poor clinical outcome caused by this phenotype, detailed information regarding its decisive virulence genes and factors affecting virulence expression needs to be deciphered. Here, we demonstrate that the T3SS effector ExoU has toxic effects on mammalian cells and is required for virulence in the murine bloodstream infection model. Moreover, a functional downstream SpcU is required for ExoU secretion and cytotoxicity. This work highlights the potential role of ExoU in the pathogenesis of disease and provides a new perspective for further research on the development of new antimicrobials with antivirulence ability.

The Host-Pathogen Interplay: A Tale of Two Stories within the Cornea and Posterior Segment

Ocular infectious diseases are an important cause of potentially preventable vision loss and blindness. In the following manuscript, we will review ocular immunology and the pathogenesis of herpesviruses and Pseudomonas aeruginosa infections of the cornea and posterior segment. We will highlight areas of future research and what is currently known to promote bench-to-bedside discoveries to improve clinical outcomes of these debilitating ocular diseases.

Transcriptional Regulators Controlling Virulence in Pseudomonas aeruginosa

Pseudomonas aeruginosa is a pathogen capable of colonizing virtually every human tissue. The host colonization competence and versatility of this pathogen are powered by a wide array of virulence factors necessary in different steps of the infection process. This includes factors involved in bacterial motility and attachment, biofilm formation, the production and secretion of extracellular invasive enzymes and exotoxins, the production of toxic secondary metabolites, and the acquisition of iron. Expression of these virulence factors during infection is tightly regulated, which allows their production only when they are needed. This process optimizes host colonization and virulence. In this work, we review the intricate network of transcriptional regulators that control the expression of virulence factors in P. aeruginosa, including one- and two-component systems and σ factors. Because inhibition of virulence holds promise as a target for new antimicrobials, blocking the regulators that trigger the production of virulence determinants in P. aeruginosa is a promising strategy to fight this clinically relevant pathogen.

Infection promotes Ser-214 phosphorylation important for generation of cytotoxic tau variants

Patients who recover from hospital-acquired pneumonia exhibit a high incidence of end-organ dysfunction following hospital discharge, including cognitive deficits. We have previously demonstrated that pneumonia induces the production and release of cytotoxic oligomeric tau from pulmonary endothelial cells, and these tau oligomers can enter the circulation and may be a cause of long-term morbidities. Endothelial-derived oligomeric tau is hyperphosphorylated during infection. The purpose of these studies was to determine whether Ser-214 phosphorylation of tau is a necessary stimulus for generation of cytotoxic tau variants. The results of these studies demonstrate that Ser-214 phosphorylation is critical for the cytotoxic properties of infection-induced oligomeric tau. In the lung, Ser-214 phosphorylated tau contributes to disruption of the alveolar-capillary barrier, resulting in increased permeability. However, in the brain, both the Ser-214 phosphorylated tau and the mutant Ser-214-Ala tau, which cannot be phosphorylated, disrupted hippocampal long-term potentiation suggesting that inhibition of long-term potentiation was relatively insensitive to the phosphorylation status of Ser-214. Nonetheless, phosphorylation of tau is essential to its cytotoxicity since global dephosphorylation of the infection-induced cytotoxic tau variants rescued long-term potentiation. Collectively, these data demonstrate that multiple forms of oligomeric tau are generated during infectious pneumonia, with different forms of oligomeric tau being responsible for dysfunction of distinct end-organs during pneumonia.

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

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

Predatory bacteria can reduce Pseudomonas aeruginosa induced corneal perforation and proliferation in a rabbit keratitis model

PURPOSE

Pseudomonas aeruginosa keratitis is a severe ocular infection that can lead to perforation of the cornea. In this study we evaluated the role of bacterial quorum sensing in generating corneal perforation and bacterial proliferation and tested whether co-injection of the predatory bacteria Bdellovibrio bacteriovorus could alter the clinical outcome. P. aeruginosa with lasR mutations were observed among keratitis isolates from a study collecting samples from India, so an isogenic lasR mutant strain of P. aeruginosa was included.

METHODS

Rabbit corneas were intracorneally infected with P. aeruginosa strain PA14 or an isogenic ΔlasR mutant and co-injected with PBS or B. bacteriovorus. After 24 h, eyes were evaluated for clinical signs of infection. Samples were analyzed by scanning electron microscopy, optical coherence tomography, sectioned for histology, and corneas were homogenized for CFU enumeration and for inflammatory cytokines.

RESULTS

We observed that 54% of corneas infected by wild-type PA14 presented with a corneal perforation (n = 24), whereas only 4% of PA14 infected corneas that were co-infected with B. bacteriovorus perforate (n = 25). Wild-type P. aeruginosa proliferation was reduced 7-fold in the predatory bacteria treated eyes. The ΔlasR mutant was less able to proliferate compared to the wild-type, but was largely unaffected by B. bacteriovorus.

CONCLUSION

These studies indicate a role for bacterial quorum sensing in the ability of P. aeruginosa to proliferate and cause perforation of the rabbit cornea. Additionally, this study suggests that predatory bacteria can reduce the virulence of P. aeruginosa in an ocular prophylaxis model.

Predatory Bacteria can Reduce Pseudomonas aeruginosa Induced Corneal Perforation and Proliferation in a Rabbit Keratitis Model

Purpose

Pseudomonas aeruginosa keratitis is a severe ocular infection that can lead to perforation of the cornea. In this study we evaluated the role of bacterial quorum sensing in generating corneal perforation and bacterial proliferation and tested whether co-injection of the predatory bacteria Bdellovibrio bacteriovorus could alter the clinical outcome. P. aeruginosa with lasR mutations were observed among keratitis isolates from a study collecting samples from India, so an isogenic lasR mutant strain of P. aeruginosa was included.

Methods

Rabbit corneas were intracorneally infected with P. aeruginosa strain PA14 or an isogenic Δ lasR mutant and co-injected with PBS or B. bacteriovorus . After 24 h, eyes were evaluated for clinical signs of infection. Samples were analyzed by scanning electron microscopy, optical coherence tomography, sectioned for histology, and corneas were homogenized for CFU enumeration and for inflammatory cytokines.

Results

We observed that 54% of corneas infected by wild-type PA14 presented with a corneal perforation (n=24), whereas only 4% of PA14 infected corneas that were co-infected with B. bacteriovorus perforate (n=25). Wild-type P. aeruginosa proliferation was reduced 7-fold in the predatory bacteria treated eyes. The Δ lasR mutant was less able to proliferate compared to the wild-type, but was largely unaffected by B. bacteriovorus .

Conclusion

These studies indicate a role for bacterial quorum sensing in the ability of P. aeruginosa to proliferate and cause perforation of the rabbit cornea. Additionally, this study suggests that predatory bacteria can reduce the virulence of P. aeruginosa in an ocular prophylaxis model.

Compendium-Wide Analysis of Pseudomonas aeruginosa Core and Accessory Genes Reveals Transcriptional Patterns across Strains PAO1 and PA14

Pseudomonas aeruginosa is an opportunistic pathogen that causes difficult-to-treat infections. Two well-studied divergent P. aeruginosa strain types, PAO1 and PA14, have significant genomic heterogeneity, including diverse accessory genes present in only some strains. Genome content comparisons find core genes that are conserved across both PAO1 and PA14 strains and accessory genes that are present in only a subset of PAO1 and PA14 strains. Here, we use recently assembled transcriptome compendia of publicly available P. aeruginosa RNA sequencing (RNA-seq) samples to create two smaller compendia consisting of only strain PAO1 or strain PA14 samples with each aligned to their cognate reference genome. We confirmed strain annotations and identified other samples for inclusion by assessing each sample's median expression of PAO1-only or PA14-only accessory genes. We then compared the patterns of core gene expression in each strain. To do so, we developed a method by which we analyzed genes in terms of which genes showed similar expression patterns across strain types. We found that some core genes had consistent correlated expression patterns across both compendia, while others were less stable in an interstrain comparison. For each accessory gene, we also determined core genes with correlated expression patterns. We found that stable core genes had fewer coexpressed neighbors that were accessory genes. Overall, this approach for analyzing expression patterns across strain types can be extended to other groups of genes, like phage genes, or applied for analyzing patterns beyond groups of strains, such as samples with different traits, to reveal a deeper understanding of regulation. IMPORTANCE Pseudomonas aeruginosa is a ubiquitous pathogen. There is much diversity among P. aeruginosa strains, including two divergent but well-studied strains, PAO1 and PA14. Understanding how these different strain-level traits manifest is important for identifying targets that regulate different traits of interest. With the availability of thousands of PAO1 and PA14 samples, we created two strain-specific RNA-seq compendia where each one contains hundreds of samples from PAO1 or PA14 strains and used them to compare the expression patterns of core genes that are conserved in both strain types and to determine which core genes have expression patterns that are similar to those of accessory genes that are unique to one strain or the other using an approach that we developed. We found a subset of core genes with different transcriptional patterns across PAO1 and PA14 strains and identified those core genes with expression patterns similar to those of strain-specific accessory genes.

Pseudomonas aeruginosa Cytotoxins: Mechanisms of Cytotoxicity and Impact on Inflammatory Responses

Pseudomonas aeruginosa is one of the most virulent opportunistic Gram-negative bacterial pathogens in humans. It causes many acute and chronic infections with morbidity and mortality rates as high as 40%. P. aeruginosa owes its pathogenic versatility to a large arsenal of cell-associated and secreted virulence factors which enable this pathogen to colonize various niches within hosts and protect it from host innate immune defenses. Induction of cytotoxicity in target host cells is a major virulence strategy for P. aeruginosa during the course of infection. P. aeruginosa has invested heavily in this strategy, as manifested by a plethora of cytotoxins that can induce various forms of cell death in target host cells. In this review, we provide an in-depth review of P. aeruginosa cytotoxins based on their mechanisms of cytotoxicity and the possible consequences of their cytotoxicity on host immune responses.

Computational approach to attenuate virulence of Pseudomonas aeruginosa through bioinspired silver nanoparticles

In this study we aim to investigate the computational docking approach of biofabricated silver nanoparticles against P. aeruginosa virulent exoenzymes, such as ExoS and ExoY. Therefore, the synthesis and characterization of biofabricated silver nanoparticles using Piper betle leaves (Pb-AgNPs) were carried out. The surface topology and functional group attachment on the surface of Pb-AgNPs were analyzed using UV-visible spectroscopy, Scanning Electron Microscopy, Fourier Transformed Infrared Spectroscopy (FTIR), and X-Ray Diffraction. The FTIR analysis revealed that the synthesized silver nanoparticles were capped with P. betle phytochemicals importantly Eugenol and Hydroxychavicol. These are the major bioactive compounds present in P. betle leaves; therefore, computational docking of Eugenol-conjugated AgNPs (PbEu-AgNPs) and Hydroxychavicol-conjugated AgNPs (PbHy-AgNPs) against ExoS and ExoY was performed. The active residues of PbEu-AgNPs and PbHy-AgNPs interacted with the active site of ExoS and ExoY exoenzymes. Biofabricated AgNP-mediated inhibition of these virulent exoenzymes blocked the adverse effect of P. aeruginosa on the host cell. The computational analysis provides new approach into the design of biofabricated AgNPs as promising anti-infective nanomedicine agents.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13205-022-03367-0.

A Model of Intracellular Persistence of Pseudomonas aeruginosa in Airway Epithelial Cells

Pseudomonas aeruginosa (P.a.) is a major human pathogen capable of causing chronic infections in hosts with weakened barrier functions and host defenses, most notably airway infections commonly observed in individuals with the genetic disorder cystic fibrosis (CF). While mainly described as an extracellular pathogen, previous in vitro studies have described the molecular events leading to P.a. internalization in diverse epithelial cell types. However, the long-term fate of intracellular P.a. remains largely unknown. Here, we developed a model allowing for a better understanding of long-term (up to 120 h) intracellular bacterial survival in the airway epithelial cell line BEAS-2B. Using a tobramycin protection assay, we characterized the internalization, long-term intracellular survival, and cytotoxicity of the lab strain PAO1, as well as clinical CF isolates, and conducted analyses at the single-cell level using confocal microscopy and flow cytometry techniques. We observed that infection at low multiplicity of infection allows for intracellular survival up to 120 h post-infection without causing significant host cytotoxicity. Finally, infection with clinical isolates revealed significant strain-to-strain heterogeneity in intracellular survival, including a high persistence phenotype associated with bacterial replication within host cells. Future studies using this model will further elucidate the host and bacterial mechanisms that promote P. aeruginosa intracellular persistence in airway epithelial cells, a potentially unrecognized bacterial reservoir during chronic infections.

Using genome-wide expression compendia to study microorganisms

A gene expression compendium is a heterogeneous collection of gene expression experiments assembled from data collected for diverse purposes. The widely varied experimental conditions and genetic backgrounds across samples creates a tremendous opportunity for gaining a systems level understanding of the transcriptional responses that influence phenotypes. Variety in experimental design is particularly important for studying microbes, where the transcriptional responses integrate many signals and demonstrate plasticity across strains including response to what nutrients are available and what microbes are present. Advances in high-throughput measurement technology have made it feasible to construct compendia for many microbes. In this review we discuss how these compendia are constructed and analyzed to reveal transcriptional patterns.

Differential Roles for IL-1α and IL-1β in Pseudomonas aeruginosa Corneal Infection

Pseudomonas aeruginosa is an important cause of dermal, pulmonary, and ocular disease. Our studies have focused on P. aeruginosa infections of the cornea (keratitis) as a major cause of blinding microbial infections. The infection leads to an influx of innate immune cells, with neutrophils making up to 90% of recruited cells during early stages. We previously reported that the proinflammatory cytokines IL-1α and IL-1β were elevated during infection. Compared with wild-type (WT), infected Il1b-/- mice developed more severe corneal disease that is associated with impaired bacterial killing as a result of defective neutrophil recruitment. We also reported that neutrophils are an important source of IL-1α and IL-1β, which peaked at 24 h postinfection. To examine the role of IL-1α compared with IL-1β in P. aeruginosa keratitis, we inoculated corneas of C57BL/6 (WT), Il1a-/-, Il1b-/-, and Il1a-/-Il1b-/- (double-knockout) mice with 5 × 104 ExoS-expressing P. aeruginosa. Il1b-/- and double-knockout mice have significantly higher bacterial burden that was consistent with delayed neutrophil and monocyte recruitment to the corneas. Surprisingly, Il1a-/- mice had the opposite phenotype with enhanced bacteria clearance compared with WT mice. Although there were no significant differences in neutrophil recruitment, Il1a-/- neutrophils displayed a more proinflammatory transcriptomic profile compared to WT with elevations in C1q expression that likely caused the phenotypic differences observed. To our knowledge, our findings identify a novel, non-redundant role for IL-1α in impairing bacterial clearance.

Pseudomonas aeruginosa Alters Critical Lung Epithelial Cell Functions through Activation of ADAM17

Severe epithelial dysfunction is one major hallmark throughout the pathophysiological progress of bacterial pneumonia. Junctional and cellular adhesion molecules (e.g., JAMA-A, ICAM-1), cytokines (e.g., TNFα), and growth factors (e.g., TGFα), controlling proper lung barrier function and leukocyte recruitment, are proteolytically cleaved and released into the extracellular space through a disintegrin and metalloproteinase (ADAM) 17. In cell-based assays, we could show that the protein expression, maturation, and activation of ADAM17 is upregulated upon infection of lung epithelial cells with Pseudomonas aeruginosa and Exotoxin A (ExoA), without any impact of infection by Streptococcus pneumoniae. The characterization of released extracellular vesicles/exosomes and the comparison to heat-inactivated bacteria revealed that this increase occurred in a cell-associated and toxin-dependent manner. Pharmacological targeting and gene silencing of ADAM17 showed that its activation during infection with Pseudomonas aeruginosa was critical for the cleavage of junctional adhesion molecule A (JAM-A) and epithelial cell survival, both modulating barrier integrity, epithelial regeneration, leukocyte adhesion and transepithelial migration. Thus, site-specific targeting of ADAM17 or blockage of the activating toxins may constitute a novel anti-infective therapeutic option in Pseudomonas aeruginosa lung infection preventing severe epithelial and organ dysfunctions and stimulating future translational studies.

Regulation of T3SS synthesis, assembly and secretion in Pseudomonas aeruginosa

T3SS is an important virulence factor of Pseudomonas aeruginosa and has a central role in the infection process. However, the functional regulation of the T3SS by environmental signals is poorly understood. In our lab, we use fluorescence microscopy to study protein kinetics in real-time in live cells. In P. aeruginosa, results have shown that T3SS appears as bright foci at the cell membrane with no specific arrangement. In addition, T3SS is tightly controlled as it appears under a limited time period with the highest intensity at 3 h then disappears. Surprisingly, only 2.5% of the all assembled T3SS in the population have detectable ExoS synthesis. While T3SS assembly and ExoS synthesis increased under high salt concentration, they unexpectedly were not affected by different cyclic di-GMP levels. On the other hand, T3SS itself has an effect on the cyclic di-GMP levels inside the cell. Data have shown that despite T3SS in P. aeruginosa and Yersinia enterocolitica belong to the same the group, the two systems differentiate greatly in activity and regulation. We can conclude that every T3SS is unique and thus further studies are needed to elucidate the functional regulation of each system to better help effective inhibitor design.

Role of Host and Bacterial Lipids in Pseudomonas aeruginosa Respiratory Infections

The opportunistic pathogen Pseudomonas aeruginosa is one of the most common agents of respiratory infections and has been associated with high morbidity and mortality rates. The ability of P. aeruginosa to cause severe respiratory infections results from the coordinated action of a variety of virulence factors that promote bacterial persistence in the lungs. Several of these P. aeruginosa virulence mechanisms are mediated by bacterial lipids, mainly lipopolysaccharide, rhamnolipid, and outer membrane vesicles. Other mechanisms arise from the activity of P. aeruginosa enzymes, particularly ExoU, phospholipase C, and lipoxygenase A, which modulate host lipid signaling pathways. Moreover, host phospholipases, such as cPLA2α and sPLA2, are also activated during the infectious process and play important roles in P. aeruginosa pathogenesis. These mechanisms affect key points of the P. aeruginosa-host interaction, such as: i) biofilm formation that contributes to bacterial colonization and survival, ii) invasion of tissue barriers that allows bacterial dissemination, iii) modulation of inflammatory responses, and iv) escape from host defenses. In this mini-review, we present the lipid-based mechanism that interferes with the establishment of P. aeruginosa in the lungs and discuss how bacterial and host lipids can impact the outcome of P. aeruginosa respiratory infections.

Genomic Surveillance of Clinical Pseudomonas aeruginosa Isolates Reveals an Additive Effect of Carbapenemase Production on Carbapenem Resistance

Carbapenem resistance in Pseudomonas aeruginosa is increasing globally, and surveillance to define the mechanisms of such resistance in low- and middle-income countries is limited. This study establishes the genotypic mechanisms of β-lactam resistance by whole-genome sequencing (WGS) in 142 P. aeruginosa clinical isolates recovered from three hospitals in Islamabad and Rawalpindi, Pakistan between 2016 and 2017. Isolates were subjected to antimicrobial susceptibility testing (AST) by Kirby-Bauer disk diffusion, and their genomes were assembled from Illumina sequencing data. β-lactam resistance was high, with 46% of isolates resistant to piperacillin-tazobactam, 42% to cefepime, 48% to ceftolozane-tazobactam, and 65% to at least one carbapenem. Twenty-two percent of isolates were resistant to all β-lactams tested. WGS revealed that carbapenem resistance was associated with the acquisition of metallo-β-lactamases (MBLs) or extended-spectrum β-lactamases (ESBLs) in the blaGES, blaVIM, and blaNDM families, and mutations in the porin gene oprD. These resistance determinants were found in globally distributed lineages, including ST235 and ST664, as well as multiple novel STs which have been described in a separate investigation. Analysis of AST results revealed that acquisition of MBLs/ESBLs on top of porin mutations had an additive effect on imipenem resistance, suggesting that there is a selective benefit for clinical isolates to encode multiple resistance determinants to the same drugs. The strong association of these resistance determinants with phylogenetic background displays the utility of WGS for monitoring carbapenem resistance in P. aeruginosa, while the presence of these determinants throughout the phylogenetic tree shows that knowledge of the local epidemiology is crucial for guiding potential treatment of multidrug-resistant P. aeruginosa infections. IMPORTANCE Pseudomonas aeruginosa is associated with serious infections, and treatment can be challenging. Because of this, carbapenems and β-lactam/β-lactamase inhibitor combinations have become critical tools in treating multidrug-resistant (MDR) P. aeruginosa infections, but increasing resistance threatens their efficacy. Here, we used WGS to study the genotypic and phylogenomic patterns of 142 P. aeruginosa isolates from the Potohar region of Pakistan. We sequenced both MDR and antimicrobial susceptible isolates and found that while genotypic and phenotypic patterns of antibiotic resistance correlated with phylogenomic background, populations of MDR P. aeruginosa were found in all major phylogroups. We also found that isolates possessing multiple resistance mechanisms had significantly higher levels of imipenem resistance compared to the isolates with a single resistance mechanism. This study demonstrates the utility of WGS for monitoring patterns of antibiotic resistance in P. aeruginosa and potentially guiding treatment choices based on the local spread of β-lactamase genes.

Chimeric bacteriocin S5-PmnH engineered by domain swapping efficiently controls Pseudomonas aeruginosa infection in murine keratitis and lung models

Rampant rise of multidrug resistant strains among Gram-negative bacteria has necessitated investigation of alternative antimicrobial agents with novel modes of action including antimicrobial proteins such as bacteriocins. The main hurdle in the clinical development of bacteriocin biologics is their narrow specificity and limited strain activity spectrum. Genome mining of bacteria for broadly active bacteriocins have identified a number of promising candidates but attempts to improve these natural multidomain proteins further, for example by combining domains of different origin, have so far met with limited success. We have found that domain swapping of Pseudomonas bacteriocins of porin type, when carried out between phylogenetically related molecules with similar mechanism of activity, allows the generation of highly active molecules with broader spectrum of activity, for example by abolishing strain resistance due to the presence of immunity proteins. The most broadly active chimera engineered in this study, S5-PmnH, exhibits excellent control of Pseudomonas aeruginosa infection in validated murine keratitis and lung infection models.

The Pseudomonas aeruginosa Type III Secretion System Exoenzyme Effector ExoU Induces Mitochondrial Damage in a Murine Bone Marrow-Derived Macrophage Infection Model

Pseudomonas aeruginosa is a Gram-negative, opportunistic pathogen that causes nosocomial pneumonia, urinary tract infections, and bacteremia. A hallmark of P. aeruginosa pathogenesis is disruption of host cell function by the type III secretion system (T3SS) and its cognate exoenzyme effectors. The T3SS effector ExoU is phospholipase A2 (PLA2) that targets the host cell plasmalemmal membrane to induce cytolysis and is an important virulence factor that mediates immune avoidance. In addition, ExoU has been shown to subvert the host inflammatory response in a noncytolytic manner. In primary bone marrow-derived macrophages (BMDMs), P. aeruginosa infection is sensed by the nucleotide-binding domain containing leucine-rich repeats-like receptor 4 (NLRC4) inflammasome, which triggers caspase-1 activation and inflammation. ExoU transiently inhibits NLRC4 inflammasome-mediated activation of caspase-1 and its downstream target, interleukin 1β (IL-1β), to suppress activation of inflammation. In the present study, we sought to identify additional noncytolytic virulence functions for ExoU and discovered an unexpected association between ExoU, host mitochondria, and NLRC4. We show that infection of BMDMs with P. aeruginosa strains expressing ExoU elicited mitochondrial oxidative stress. In addition, mitochondria and mitochondrion-associated membrane fractions enriched from infected cells exhibited evidence of autophagy activation, indicative of damage. The observation that ExoU elicited mitochondrial stress and damage suggested that ExoU may also associate with mitochondria during infection. Indeed, ExoU phospholipase A2 enzymatic activity was present in enriched mitochondria and mitochondrion-associated membrane fractions isolated from P. aeruginosa-infected BMDMs. Intriguingly, enriched mitochondria and mitochondrion-associated membrane fractions isolated from infected Nlrc4 homozygous knockout BMDMs displayed significantly lower levels of ExoU enzyme activity, suggesting that NLRC4 plays a role in the ExoU-mitochondrion association. These observations prompted us to assay enriched mitochondria and mitochondrion-associated membrane fractions for NLRC4, caspase-1, and IL-1β. NLRC4 and pro-caspase-1 were detected in enriched mitochondria and mitochondrion-associated membrane fractions isolated from noninfected BMDMs, and active caspase-1 and active IL-1β were detected in response to P. aeruginosa infection. Interestingly, ExoU inhibited mitochondrion-associated caspase-1 and IL-1β activation. The implications of ExoU-mediated effects on mitochondria and the NLRC4 inflammasome during P. aeruginosa infection are discussed.

Therapeutic Effects of Hyaluronic Acid Against Cytotoxic Extracellular Vesicles Released During Pseudomonas Aeruginosa Pneumonia

ABSTRACT

Extracellular vesicles (EVs) have now been recognized as important mediators of cellular communication during injury and repair. We previously found that plasma EVs isolated from ex vivo perfused human lungs injured with Escherichia coli bacterial pneumonia were inflammatory, and exogenous administration of high molecular weight (HMW) hyaluronic acid (HA) as therapy bound to these EVs, decreasing inflammation and injury. In the current study, we studied the role of EVs released during severe Pseudomonas aeruginosa (PA) pneumonia in mice and determined whether intravenous administration of exogenous HMW HA would have therapeutic effects against the bacterial pneumonia. EVs were collected from the bronchoalveolar lavage fluid (BALF) of mice infected with PA103 by ultracentrifugation and analyzed by NanoSight and flow cytometry. In a cytotoxicity assay, administration of EVs released from infected mice (I-EVs) decreased the viability of A549 cells compared to EV isolated from sham control mice (C-EVs). Either exogenous HMW HA or an anti-CD44 antibody, when co-incubated with I-EVs, significantly improved the viability of the A549 cells. In mice with PA103 pneumonia, administration of HMW HA improved pulmonary edema and bacterial count in the lungs and decreased TNF-α and caspase-3 levels in the supernatant of lung homogenates. In conclusion, EVs isolated from BALF of mice with P. aeruginosa pneumonia were cytotoxic and inflammatory, and intravenous HMW HA administration was protective against P. aeruginosa pneumonia.

The Psychrotrophic Pseudomonas lundensis, a Non-aeruginosa Pseudomonad, Has a Type III Secretion System of the Ysc Family, Which Is Transcriptionally Active at 37°C

The type III secretion system (T3SS) is a needle-like structure found in Gram-negative pathogens that directly delivers virulence factors like toxins and effector molecules into eukaryotic cells. The T3SS is classified into different families according to the type of effector and host. Of these, the Ysc family T3SS, found in Yersinia species and Pseudomonas aeruginosa, confers high virulence to bacteria against eukaryotic hosts. Here, we present the first identification and transcriptional analyses of a Ysc T3SS in a non-aeruginosa Pseudomonas species, Pseudomonas lundensis, an environmental psychrotrophic bacterium and important agent of frozen food spoilage. We have identified and sequenced isolates of P. lundensis from three very distinct ecological niches (Antarctic temporary meltwater pond, U.S. supermarket 1% pasteurized milk, and cystic fibrosis lungs) and compared these to previously reported food spoilage isolates in Europe. In this paper, we show that strains of P. lundensis isolated from these diverse environments with ambient temperatures ranging from below freezing to 37°C all possess a Ysc family T3SS secretion system and a T3S effector, ExoU. Using in vitro and in vivo transcriptomics, we show that the T3SS in P. lundensis is transcriptionally active, is expressed more highly at mammalian body temperature (37°C) than 4°C, and has even higher expression levels when colonizing a host environment (mouse intestine). Thus, this Ysc T3SS-expressing psychrotrophic Pseudomonad has an even greater range of growth niches than previously appreciated, including diseased human airways. IMPORTANCE P. lundensis strains have been isolated from environments that are distinct and diverse in both nutrient availability and environmental pressures (cold food spoilage, Antarctic melt ponds, cystic fibrosis lungs). As a species, this bacterium can grow in diverse niches that markedly vary in available nutrients and temperature, and in our study, we show that these various strains share greater than 99% sequence similarity. In addition, all isolates studied here encoded complete homologs of the Ysc family T3SS seen in P. aeruginosa. Until recently, P. aeruginosa has remained as the only Pseudomonas species to have a characterized functional Ysc (Psc) family T3SS. With the identification of a complete Ysc T3SS in P. lundensis that is expressed at 37°C in vivo, it is intriguing to wonder whether this bacterium may indeed have some level of symbiotic activity, of yet unknown type, when consumed by a mammalian host.

ExoU Induces Lung Endothelial Cell Damage and Activates Pro-Inflammatory Caspase-1 during Pseudomonas aeruginosa Infection

The Gram-negative, opportunistic pathogen Pseudomonas aeruginosa utilizes a type III secretion system to inject exoenzyme effectors into a target host cell. Of the four best-studied exoenzymes, ExoU causes rapid cell damage and death. ExoU is a phospholipase A₂ (PLA₂) that hydrolyses host cell membranes, and P. aeruginosa strains expressing ExoU are associated with poor outcomes in critically ill patients with pneumonia. While the effects of ExoU on lung epithelial and immune cells are well studied, a role for ExoU in disrupting lung endothelial cell function has only recently emerged. Lung endothelial cells maintain a barrier to fluid and protein flux into tissue and airspaces and regulate inflammation. Herein, we describe a pulmonary microvascular endothelial cell (PMVEC) culture infection model to examine the effects of ExoU. Using characterized P. aeruginosa strains and primary clinical isolates, we show that strains expressing ExoU disrupt PMVEC barrier function by causing substantial PMVEC damage and lysis, in a PLA₂-dependent manner. In addition, we show that strains expressing ExoU activate the pro-inflammatory caspase-1, in a PLA₂-dependent manner. Considering the important roles for mitochondria and oxidative stress in regulating inflammatory responses, we next examined the effects of ExoU on reactive oxygen species production. Infection of PMVECs with P. aeruginosa strains expressing ExoU triggered a robust oxidative stress compared to strains expressing other exoenzyme effectors. We also provide evidence that, intriguingly, ExoU PLA₂ activity was detectable in mitochondria and mitochondria-associated membrane fractions isolated from P. aeruginosa-infected PMVECs. Interestingly, ExoU-mediated activation of caspase-1 was partially inhibited by reactive oxygen species scavengers. Together, these data suggest ExoU exerts pleiotropic effects on PMVEC function during P. aeruginosa infection that may inhibit endothelial barrier and inflammatory functions.

Exotoxin S secreted by internalized Pseudomonas aeruginosa delays lytic host cell death

The Pseudomonas aeruginosa toxin ExoS, secreted by the type III secretion system (T3SS), supports intracellular persistence via its ADP-ribosyltransferase (ADPr) activity. For epithelial cells, this involves inhibiting vacuole acidification, promoting vacuolar escape, countering autophagy, and niche construction in the cytoplasm and within plasma membrane blebs. Paradoxically, ExoS and other P. aeruginosa T3SS effectors can also have antiphagocytic and cytotoxic activities. Here, we sought to reconcile these apparently contradictory activities of ExoS by studying the relationships between intracellular persistence and host epithelial cell death. Methods involved quantitative imaging and the use of antibiotics that vary in host cell membrane permeability to selectively kill intracellular and extracellular populations after invasion. Results showed that intracellular P. aeruginosa mutants lacking T3SS effector toxins could kill (permeabilize) cells when extracellular bacteria were eliminated. Surprisingly, wild-type strain PAO1 (encoding ExoS, ExoT and ExoY) caused cell death more slowly, the time extended from 5.2 to 9.5 h for corneal epithelial cells and from 10.2 to 13.0 h for HeLa cells. Use of specific mutants/complementation and controls for initial invasion showed that ExoS ADPr activity delayed cell death. Triggering T3SS expression only after bacteria invaded cells using rhamnose-induction in T3SS mutants rescued the ExoS-dependent intracellular phenotype, showing that injected effectors from extracellular bacteria were not required. The ADPr activity of ExoS was further found to support internalization by countering the antiphagocytic activity of both the ExoS and ExoT RhoGAP domains. Together, these results show two additional roles for ExoS ADPr activity in supporting the intracellular lifestyle of P. aeruginosa; suppression of host cell death to preserve a replicative niche and inhibition of T3SS effector antiphagocytic activities to allow invasion. These findings add to the growing body of evidence that ExoS-encoding (invasive) P. aeruginosa strains can be facultative intracellular pathogens, and that intracellularly secreted T3SS effectors contribute to pathogenesis.

While the ADPr domain of the T3SS effector ExoS plays multiple roles in the intracellular lifestyle of P. aeruginosa, ExoS can also be cytotoxic and/or antiphagocytic. Here, we show that when P. aeruginosa enters the cytosol of epithelial cells, cell death is triggered independently of T3SS effector toxins, but ExoS ADPr activity delays this to enable continued intracellular survival and replication. Using rhamnose induction to express the T3SS only after invasion restored this ExoS-dependent phenotype, showing that intracellularly secreted effectors can enable intracellular pathogenesis. ExoS ADPr activity also countered antiphagocytic activity of ExoS and ExoT RhoGAP domains. These results show two additional roles for ExoS ADPr activity in promoting internalization of P. aeruginosa and protecting the intracellular niche, continuing to challenge the notions that P. aeruginosa is exclusively an extracellular pathogen, that it needs to inject T3SS effectors across plasma membranes, and that ExoS is necessarily cytotoxic to host cells.

Utilizing in silico and in vitro methods to identify possible binding sites of a novel ligand against Pseudomonas aeruginosa phospholipase toxin ExoU

Multi-drug resistant infections caused by the opportunistic pathogen, Pseudomonas aeruginosa (P. aeruginosa), are a continuing problem that contribute to morbidity and mortality in immunocompromised hosts such as cystic fibrosis (CF), wound and burn patients. The bacterial toxin ExoU is one of four potent toxins that P. aeruginosa secretes into the epithelial cells of hosts. In this study, NMR Saturation Transfer Difference (STD) and in silico Schrödinger Computational Modeling were used to identify a possible binding site of a novel ligand methoctramine targeting ExoU. Future project goals will be to design a structure activity relationship (SAR) study of methoctramine and ExoU and lead to a new drug solving ExoU toxicity P. aeruginosa exerts in the clinical environment.

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STD-NMR identified a weak binding molecule for ExoU.

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Schrödinger's SiteMap tool to identify potential binding sites of methoctramine to ExoU.

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Positively charged protonated amines on methoctramine allows for multiple salt bridge and H-bond interactions.

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Top ranked druggable site aligns and corresponds to ExoU C-terminus region.

Pseudomonas aeruginosa Antivirulence Strategies: Targeting the Type III Secretion System

The Pseudomonas aeruginosa type III secretion system (T3SS) is a complex molecular machine that delivers toxic proteins from the bacterial cytoplasm directly into host cells. This apparatus spans the inner and outer membrane and employs a needle-like structure that penetrates through the eucaryotic cell membrane into the host cell cytosol. The expression of the P. aeruginosa T3SS is highly regulated by environmental signals including low calcium and host cell contact. P. aeruginosa strains with mutations in T3SS genes are less pathogenic, suggesting that the T3SS is a virulence mechanism. Given that P. aeruginosa is naturally antibiotic resistant and multidrug resistant isolates are rapidly emerging, new antibiotics to target P. aeruginosa are needed. Furthermore, even if new antibiotics were to be developed, the timeline between when an antibiotic is released and resistance development is relatively short. Therefore, the concept of targeting virulence factors has garnered attention. So-called "antivirulence" approaches do not kill the microbe but instead focus on rendering it harmless and therefore unable to cause damage. Since these therapies target a particular system or pathway, the normal microbiome is unlikely to be affected and there is less concern about the spread to other microbes. Finally, and most importantly, since any antivirulence drug does not kill the microbe, there should be less selective pressure to develop resistance to these inhibitors. The P. aeruginosa T3SS has been well studied due to its importance for pathogenesis in numerous human and animal infections. Thus, many P. aeruginosa T3SS inhibitors have been described as potential antivirulence therapeutics, some of which have progressed to clinical trials.

Delivering the pain: an overview of the type III secretion system with special consideration for aquatic pathogens

Gram-negative bacteria are known to subvert eukaryotic cell physiological mechanisms using a wide array of virulence factors, among which the type three-secretion system (T3SS) is often one of the most important. The T3SS constitutes a needle-like apparatus that the bacterium uses to inject a diverse set of effector proteins directly into the cytoplasm of the host cells where they can hamper the host cellular machinery for a variety of purposes. While the structure of the T3SS is somewhat conserved and well described, effector proteins are much more diverse and specific for each pathogen. The T3SS can remodel the cytoskeleton integrity to promote intracellular invasion, as well as silence specific eukaryotic cell signals, notably to hinder or elude the immune response and cause apoptosis. This is also the case in aquatic bacterial pathogens where the T3SS can often play a central role in the establishment of disease, although it remains understudied in several species of important fish pathogens, notably in Yersinia ruckeri. In the present review, we summarise what is known of the T3SS, with a special focus on aquatic pathogens and suggest some possible avenues for research including the potential to target the T3SS for the development of new anti-virulence drugs.

Characterizing the Type 6 Secretion System (T6SS) and its role in the virulence of avian pathogenic Escherichia coli strain APECO18

Avian pathogenic E. coli is the causative agent of extra-intestinal infections in birds known as colibacillosis, which can manifest as localized or systemic infections. The disease affects all stages of poultry production, resulting in economic losses that occur due to morbidity, carcass condemnation and increased mortality of the birds. APEC strains have a diverse virulence trait repertoire, which includes virulence factors involved in adherence to and invasion of the host cells, serum resistance factors, and toxins. However, the pathogenesis of APEC infections remains to be fully elucidated. The Type 6 secretion (T6SS) system has recently gained attention due to its role in the infection process and protection of bacteria from host defenses in human and animal pathogens. Previous work has shown that T6SS components are involved in the adherence to and invasion of host cells, as well as in the formation of biofilm, and intramacrophage bacterial replication. Here, we analyzed the frequency of T6SS genes hcp, impK, evpB, vasK and icmF in a collection of APEC strains and their potential role in virulence-associated phenotypes of APECO18. The T6SS genes were found to be significantly more prevalent in APEC than in fecal E. coli isolates from healthy birds. Expression of T6SS genes was analyzed in culture media and upon contact with host cells. Mutants were generated for hcp, impK, evpB, and icmF and characterized for their impact on virulence-associated phenotypes, including adherence to and invasion of host model cells, and resistance to predation by Dictyostelium discoideum. Deletion of the aforementioned genes did not significantly affect adherence and invasion capabilities of APECO18. Deletion of hcp reduced resistance of APECO18 to predation by D. discoideum, suggesting that T6SS is involved in the virulence of APECO18.

A panel of diverse Pseudomonas aeruginosa clinical isolates for research and development

Objectives

Pseudomonas aeruginosa is a leading cause of community- and hospital-acquired infections. Successful treatment is hampered by its remarkable ability to rapidly develop resistance to antimicrobial agents, primarily through mutation. In response, WHO listed carbapenem-resistant P. aeruginosa as a Priority 1 (Critical) pathogen for research and development of new treatments. A key resource in developing effective countermeasures is access to diverse and clinically relevant strains for testing. Herein we describe a panel of 100 diverse P. aeruginosa strains to support this endeavour.

Methods

WGS was performed on 3785 P. aeruginosa isolates in our repository. Isolates were cultured from clinical samples collected from healthcare facilities around the world between 2003 and 2017. Core-genome MLST and high-resolution SNP-based phylogenetic analyses were used to select a panel of 100 strains that captured the genetic diversity of this collection. Antibiotic susceptibility testing was also performed using 14 clinically relevant antibiotics.

Results

This 100-strain diversity panel contained representative strains from 91 different STs, including genetically distinct strains from major epidemic clones ST-111, ST-235, ST-244 and ST-253. Seventy-one distinct antibiotic susceptibility profiles were identified ranging from pan-susceptible to pan-resistant. Known resistance alleles as well as the most prevalent mutations underlying the antibiotic susceptibilities were characterized for all isolates.

Conclusions

This panel provides a diverse and comprehensive set of P. aeruginosa strains for use in developing solutions to antibiotic resistance. The isolates and available metadata, including genome sequences, are available to industry, academia, federal and other laboratories at no additional cost.

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.

Anti-virulence Bispecific Monoclonal Antibody Mediated Protection Against Pseudomonas aeruginosa Ventilator-Associated Pneumonia in a Rabbit Model

Ventilator-associated pneumonia is an important clinical manifestation of the nosocomial pathogen Pseudomonas aeruginosa. We characterized the correlates of protection of MEDI3902, a bispecific human IgG1 mAb that targets the P. aeruginosa type-3-secretion PcrV protein and the Psl exopolysaccharide, in a rabbit model of ventilator-associated pneumonia using lung-protective, low-tidal volume mechanical ventilation. Rabbits infused with MEDI3902 prophylactically were protected, whereas those pretreated with irrelevant isotype-control IgG (c-IgG) succumbed between 12 and 44 hours post infection [100% (8/8) vs. 0% (8/8) survival, P<0.01 by log-rank test]. Lungs from rabbits pretreated with c-IgG, but not those with MEDI3902, had bilateral, multifocal areas of marked necrosis, hemorrhage, neutrophilic inflammatory infiltrate, diffuse fibrinous edema in alveolar spaces. All rabbits pretreated with c-IgG developed worsening bacteremia that peaked at the time of death, whereas only 38% (3/8) rabbits pretreated with MEDI3902 developed such high-grade bacteremia (two-sided Fisher's exact test, P=0.026). Biomarkers associated with acute respiratory distress syndrome were evaluated longitudinally in blood samples collected every 2-4 hours to assess systemic pathophysiological changes in rabbits pretreated with MEDI3902 or c-IgG. Biomarkers were sharply increased or decreased in rabbits pretreated with c-IgG, but not those pretreated with MEDI3902, including ratio of arterial oxygen partial pressure to fractional inspired oxygen PaO₂/FiO₂ <300, hypercapnia or hypocapnia, severe lactic acidosis, leukopenia and neutropenia. Cytokines and chemokines associated with ARDS were significantly downregulated in lungs from rabbits pretreated with MEDI3902 compared with c-IgG. These results suggest that MEDI3902 prophylaxis could have potential clinical utility for decreasing severity of P. aeruginosa ventilator-associated pneumonia.

Perspectives on the Pseudomonas aeruginosa Type III Secretion System Effector ExoU and Its Subversion of the Host Innate Immune Response to Infection

Pseudomonas aeruginosa is an opportunistic, Gram-negative pathogen and an important cause of hospital acquired infections, especially in immunocompromised patients. Highly virulent P. aeruginosa strains use a type III secretion system (T3SS) to inject exoenzyme effectors directly into the cytoplasm of a target host cell. P. aeruginosa strains that express the T3SS effector, ExoU, associate with adverse outcomes in critically ill patients with pneumonia, owing to the ability of ExoU to rapidly damage host cell membranes and subvert the innate immune response to infection. Herein, we review the structure, function, regulation, and virulence characteristics of the T3SS effector ExoU, a highly cytotoxic phospholipase A2 enzyme.

The Role of Pseudomonas aeruginosa Virulence Factors in Cytoskeletal Dysregulation and Lung Barrier Dysfunction

Pseudomonas (P.) aeruginosa is an opportunistic pathogen that causes serious infections and hospital-acquired pneumonia in immunocompromised patients. P. aeruginosa accounts for up to 20% of all cases of hospital-acquired pneumonia, with an attributable mortality rate of ~30-40%. The poor clinical outcome of P. aeruginosa-induced pneumonia is ascribed to its ability to disrupt lung barrier integrity, leading to the development of lung edema and bacteremia. Airway epithelial and endothelial cells are important architecture blocks that protect the lung from invading pathogens. P. aeruginosa produces a number of virulence factors that can modulate barrier function, directly or indirectly, through exploiting cytoskeleton networks and intercellular junctional complexes in eukaryotic cells. This review summarizes the current knowledge on P. aeruginosa virulence factors, their effects on the regulation of the cytoskeletal network and associated components, and molecular mechanisms regulating barrier function in airway epithelial and endothelial cells. A better understanding of these processes will help to lay the foundation for new therapeutic approaches against P. aeruginosa-induced pneumonia.