Pseudomonas aeruginosa in Chronic Lung Infections: How to Adapt Within the Host?

Neutrophils and galectin-3 defend mice from lethal bacterial infection and humans from acute respiratory failure

Respiratory infection by Pseudomonas aeruginosa, common in hospitalized immunocompromised and immunocompetent ventilated patients, can be life-threatening because of antibiotic resistance. This raises the question of whether the host's immune system can be educated to combat this bacterium. Here we show that prior exposure to a single low dose of lipopolysaccharide (LPS) protects mice from a lethal infection by P. aeruginosa. LPS exposure trained the innate immune system by promoting expansion of neutrophil and interstitial macrophage populations distinguishable from other immune cells with enrichment of gene sets for phagocytosis- and cell-killing-associated genes. The cell-killing gene set in the neutrophil population uniquely expressed Lgals3, which encodes the multifunctional antibacterial protein, galectin-3. Intravital imaging for bacterial phagocytosis, assessment of bacterial killing and neutrophil-associated galectin-3 protein levels together with use of galectin-3-deficient mice collectively highlight neutrophils and galectin-3 as central players in LPS-mediated protection. Patients with acute respiratory failure revealed significantly higher galectin-3 levels in endotracheal aspirates (ETAs) of survivors compared to non-survivors, galectin-3 levels strongly correlating with a neutrophil signature in the ETAs and a prognostically favorable hypoinflammatory plasma biomarker subphenotype. Taken together, our study provides impetus for harnessing the potential of galectin-3-expressing neutrophils to protect from lethal infections and respiratory failure.

Model-driven characterization of functional diversity of Pseudomonas aeruginosa clinical isolates with broadly representative phenotypes

Pseudomonas aeruginosa is a leading cause of infections in immunocompromised individuals and in healthcare settings. This study aims to understand the relationships between phenotypic diversity and the functional metabolic landscape of P. aeruginosa clinical isolates. To better understand the metabolic repertoire of P. aeruginosa in infection, we deeply profiled a representative set from a library of 971 clinical P. aeruginosa isolates with corresponding patient metadata and bacterial phenotypes. The genotypic clustering based on whole-genome sequencing of the isolates, multilocus sequence types, and the phenotypic clustering generated from a multi-parametric analysis were compared to each other to assess the genotype-phenotype correlation. Genome-scale metabolic network reconstructions were developed for each isolate through amendments to an existing PA14 network reconstruction. These network reconstructions show diverse metabolic functionalities and enhance the collective P. aeruginosa pangenome metabolic repertoire. Characterizing this rich set of clinical P. aeruginosa isolates allows for a deeper understanding of the genotypic and metabolic diversity of the pathogen in a clinical setting and lays a foundation for further investigation of the metabolic landscape of this pathogen and host-associated metabolic differences during infection.

Iron starvation increases the production of the Pseudomonas aeruginosa RsmY and RsmZ sRNAs in static conditions

Pseudomonas aeruginosa is an opportunistic Gram-negative pathogen that induces virulence gene expression in response to host-mediated iron starvation. Recently, our laboratory showed that some virulence factors are responsive to iron limitation in static but not shaking growth conditions. One of these is the HSI-2-type six secretion system (T6SS), which is also induced during chronic infection. Iron regulation of T6SS was partially impacted by the iron-responsive PrrF sRNA and completely dependent upon the Pseudomonas quinolone signal (PQS) biosynthetic gene pqsA. Here, we analyzed the impact of iron on the expression of two small regulatory RNAs (sRNAs), RsmY and RsmZ, that activate the expression of T6SS by sequestering the RsmA translation inhibitor. Our results demonstrate that iron starvation induces the expression of RsmY and RsmZ in static but not shaking cultures. We further show that this induction occurs through the rsmY and rsmZ promoters and is dependent upon PqsA. Disruption of either the pqsR gene also eliminated iron-dependent regulation of rsmY and rsmZ promoter activity. Taken together, our results show novel targets of iron regulation that are specific to static growth, highlighting the importance of studying regulatory mechanisms in static communities that may be more representative of growth during chronic infection.IMPORTANCEIron is a central component of various bacterial metabolic pathways making it an important host-acquired nutrient for pathogens to establish infection. Previous iron regulatory studies primarily relied on shaking bacterial cultures; while these ensure cultural homogeneity, they do not reflect growth conditions during infection. We recently showed that static growth of Pseudomonas aeruginosa promotes iron-dependent regulation of a type six secretion system (T6SS), a virulence factor that is induced during chronic infections. In the current study, we found that static growth also promotes iron-dependent regulation of the RsmY and RsmZ sRNAs, which are global regulators that affect T6SS during chronic P. aeruginosa lung infection. Hence, our work demonstrates the Rsm sRNAs as potential effectors of iron regulation during static growth that may also be relevant in chronic infection.

AAV-vectored expression of monospecific or bispecific monoclonal antibodies protects mice from lethal Pseudomonas aeruginosa pneumonia

Pseudomonas aeruginosa poses a significant threat to immunocompromised individuals and those with cystic fibrosis. Treatment relies on antibiotics, but persistent infections occur due to intrinsic and acquired resistance of P. aeruginosa towards multiple classes of antibiotics. To date, there are no licensed vaccines for this pathogen, prompting the urgent need for novel treatment approaches to combat P. aeruginosa infection and persistence. Here we validated AAV vectored immunoprophylaxis as a strategy to generate long-term plasma and mucosal expression of highly protective monoclonal antibodies (mAbs) targeting the exopolysaccharide Psl (Cam-003) and the PcrV (V2L2MD) component of the type-III secretion system injectosome either as single mAbs or together as a bispecific mAb (MEDI3902) in a mouse model. When administered intramuscularly, AAV-αPcrV, AAV-αPsl, and AAV-MEDI3902 significantly protected mice challenged intranasally with a lethal dose of P. aeruginosa strains PAO1 and PA14 and reduced bacterial burden and dissemination to other organs. While all AAV-mAbs provided protection, AAV-αPcrV and AAV-MEDI3902 provided 100% and 87.5% protection from a lethal challenge with 4.47 × 107 CFU PAO1 and 87.5% and 75% protection from a lethal challenge with 3 × 107 CFU PA14, respectively. Serum concentrations of MEDI3902 were ~10× lower than that of αPcrV, but mice treated with this vector showed a greater reduction in bacterial dissemination to the liver, lung, spleen, and blood compared to other AAV-mAbs. These results support further investigation into the use of AAV vectored immunoprophylaxis to prevent and treat P. aeruginosa infections and other bacterial pathogens of public health concern for which current treatment strategies are limited.

In vitro activity of human defensins HNP-1 and hBD-3 against multidrug-resistant ESKAPE Gram-negatives of clinical origin and selected peptidoglycan recycling-defective mutants

The use of immune compounds as antimicrobial adjuvants is a classic idea recovering timeliness in the current antibiotic resistance scenario. However, the activity of certain antimicrobial peptides against ESKAPE Gram-negatives has not been sufficiently investigated. The objective of this study was to determine the activities of human defensins HNP-1 and hBD-3 alone or combined with permeabilizing/peptidoglycan-targeting agents against clinical ESKAPE Gram-negatives [Acinetobacter baumannii (AB), Enterobacter cloacae (EC), Klebsiella pneumoniae (KP), and acute/chronic Pseudomonas aeruginosa (PA)]. Lethal concentrations (LCs) of HNP-1 and hBD-3 were determined in four collections of multidrug resistant EC, AB, KP, and PA clinical strains (10-36 isolates depending on the collection). These defensins act through membrane permeabilization plus peptidoglycan building blockade, enabling that alterations in peptidoglycan recycling may increase their activity, which is why different recycling-defective mutants were also included. Combinations with physiological lysozyme and subinhibitory colistin for bactericidal activities determination, and with meropenem for minimum inhibitory concentrations (MICs), were also assessed. HNP-1 showed undetectable activity (LC > 32 mg/L for all strains). hBD-3 showed appreciable activities: LC ranges 2-16, 8-8, 8->32, and 8->32 mg/L for AB, EC, KP, and PA, being PA strains from cystic fibrosis significantly more resistant than acute origin ones. None of the peptidoglycan recycling-defective mutants showed greater susceptibility to HNP-1/hBD-3. Combination with colistin or lysozyme did not change their bactericidal power, and virtually neither did meropenem + hBD-3 compared to meropenem MICs. This is the first study comparatively analyzing the HNP-1/hBD-3 activities against the ESKAPE Gram-negatives, and demonstrates interesting bactericidal capacities of hBD-3 mostly against AB and EC.

IMPORTANCE

In the current scenario of critical need for new antimicrobials against multidrug-resistant bacteria, all options must be considered, including classic ideas such as the use of purified immune compounds. However, information regarding the activity of certain human defensins against ESKAPE Gram-negatives was incomplete. This is the first study comparatively assessing the in vitro activity of two membrane-permeabilizing/peptidoglycan construction-blocking defensins (HNP-1 and hBD-3) against relevant clinical collections of ESKAPE Gram-negatives, alone or in combination with permeabilizers, additional peptidoglycan-targeting attacks, or the blockade of its recycling. Our data suggest that hBD-3 has a notable bactericidal activity against multidrug-resistant Acinetobacter baumannii and Enterobacter cloacae strains that should be considered as potential adjuvant option. Our results suggest for the first time an increased resistance of Pseudomonas aeruginosa strains from chronic infection compared to acute origin ones, and provide new clues about the predominant mode of action of hBD-3 against Gram-negatives (permeabilization rather than peptidoglycan-targeting).

Cytotoxic rhamnolipid micelles drive acute virulence in Pseudomonas aeruginosa

Pseudomonas aeruginosa is an opportunistic human pathogen that has developed multi- or even pan-drug resistance toward most frontline and last resort antibiotics, leading to increasing frequency of infections and deaths among hospitalized patients, especially those with compromised immune systems. Further complicating treatment, P. aeruginosa produces numerous virulence factors that contribute to host tissue damage and immune evasion, promoting bacterial colonization and pathogenesis. In this study, we demonstrate the importance of rhamnolipid production in host-pathogen interactions. Secreted rhamnolipids form micelles that exhibited highly acute toxicity toward murine macrophages, rupturing the plasma membrane and causing organellar membrane damage within minutes of exposure. While rhamnolipid micelles (RMs) were particularly toxic to macrophages, they also caused membrane damage in human lung epithelial cells, red blood cells, Gram-positive bacteria, and even noncellular models like giant plasma membrane vesicles. Most importantly, rhamnolipid production strongly correlated with P. aeruginosa virulence against murine macrophages in various panels of clinical isolates. Altogether, our findings suggest that rhamnolipid micelles are highly cytotoxic virulence factors that drive acute cellular damage and immune evasion during P. aeruginosa infections.

Comparative analysis of antibiotic susceptibility patterns and clinical features of mucoid and non-mucoid Pseudomonas aeruginosa infections: a retrospective study

Background

Pseudomonas aeruginosa (PA) is a prevalent opportunistic pathogen that has close associations with both acute and chronic infections. However, there exists an insufficiency of accurate and comprehensive data pertaining to the antimicrobial susceptibility patterns and clinical characteristics of both mucoid and non-mucoid strains of PA (mPA and non-mPA, respectively).

Methods

From January 1, 2021 to December 31, 2022, a thorough retrospective study was carried out to examine and compare the antibiotic susceptibility test outcomes and clinical characteristics of hospitalized patients with mPA and non-mPA infections.

Results

This study investigated a cohort of 111 patients who were diagnosed with mPA infections, as well as 792 patients diagnosed with non-mPA infections. Significant demographic disparities, including gender (p < 0.001), age (p < 0.001), length of hospital stay (p < 0.001), diabetes (p = 0.043), and hypertension (p < 0.001), are evident between the mPA and non-mPA groups. The mPA group commonly necessitates hospitalization for respiratory system diseases, whereas the non-mPA group is associated with concomitant cardiovascular and cerebrovascular diseases. The mPA group demonstrates lower utilization rates of medical devices, such as Foley catheter (p < 0.001), nasogastric tube (p < 0.001), mechanical ventilation (p < 0.001), tracheostomy (p < 0.001), arterial and venous catheterization (p < 0.001), and exhibits superior organ function status, including lower incidences of hypoalbuminemia (p < 0.001), septic shock (p < 0.001), liver dysfunction (p < 0.001), renal failure (p < 0.001), and respiratory failure (p < 0.001). The non-mPA group is more vulnerable to infection with two or more bacterial pathogens compared to the mPA group, with the non-mPA group frequently resulting in Enterobacteriaceae infections and the mPA group being associated with fungal infections. Variations in antibiotic sensitivity are noted for Amikacin (p < 0.001), Ciprofloxacin (p < 0.001), Cefepime (p = 0.003), and Levofloxacin (p < 0.001) in antibiotic susceptibility testing, with resistance patterns closely tied to specific antibiotic usage.

Conclusion

There are significant demographic characteristics, clinical manifestations and antibiotic susceptibility between mPA and non-mPA infections. It is crucial to emphasize these characteristics due to their significant role in preventing and treating PA infections.

Immunometabolic Regulation of Bacterial Infection, Biofilms, and Antibiotic Susceptibility

BACKGROUND

Upon infection, mucosal tissues activate a brisk inflammatory response to clear the pathogen, i.e., resistance to disease. Resistance to disease is orchestrated by tissue-resident macrophages, which undergo profound metabolic reprogramming after sensing the pathogen. These metabolically activated macrophages release many inflammatory factors, which promote their bactericidal function. However, in immunocompetent individuals, pathogens like Pseudomonas aeruginosa, Staphylococcus aureus, and Salmonella evade this type of immunity, generating communities that thrive for the long term.

SUMMARY

These organisms develop features that render them less susceptible to eradication, such as biofilms and increased tolerance to antibiotics. Furthermore, after antibiotic therapy withdrawal, "persister" cells rapidly upsurge, triggering inflammatory relapses that worsen host health. How these pathogens persisted in inflamed tissues replete with activated macrophages remains poorly understood.

KEY MESSAGES

In this review, we discuss recent findings indicating that the ability of P. aeruginosa, S. aureus, and Salmonella to evolve biofilms and antibiotic tolerance is promoted by the similar metabolic routes that regulate macrophage metabolic reprogramming.

In vitro and in vivo evaluation of the antimicrobial effectiveness of non-medicated hydrophobic wound dressings

There is an increasing use of non-medicated wound dressing with claims of irreversible bacterial binding. Most of the data are from in vitro models which lack clinical relevance. This study employed a range of in vitro experiments to address this gap and we complemented our experimental designs with in vivo observations using dressings obtained from patients with diabetes-related foot ulcers. A hydrophobic wound dressing was compared with a control silicone dressing in vitro. Test dressings were placed on top of a Pseudomonas aeruginosa challenge suspension with increasing concentrations of suspension inoculum in addition to supplementation with phosphate buffered saline (PBS) or increased protein content (IPC). Next, we used the challenge suspensions obtained at the end of the first experiment, where bacterial loads from the suspensions were enumerated following test dressing exposure. Further, the time-dependent bacterial attachment was investigated over 1 and 24 h. Lastly, test dressings were exposed to a challenge suspension with IPC, with or without the addition of the bacteriostatic agent Deferiprone to assess the impacts of limiting bacterial growth in the experimental design. Lastly, two different wound dressings with claims of bacterial binding were obtained from patients with chronic diabetes-related foot ulcers after 72 h of application and observed using scanning electron microscope (SEM). Bacteria were enumerated from each dressing after a 1-h exposure time. There was no statistical difference in bacterial attachment between both test dressings when using different suspension inoculum concentrations or test mediums. Bacterial attachment to the two test dressings was significantly lower (p < 0.0001) when IPC was used instead of PBS. In the challenge suspension with PBS, only the hydrophobic dressing achieved a statistically significant reduction in bacterial loads (0.5 ± 0.05 log colony forming units; p = 0.001). In the presence of IPC, there was no significant reduction in bacterial loads for either test dressing. When bacterial growth was arrested, attachment to the test dressings did not increase over time, suggesting that the number of bacteria on the test dressings increases over time due to bacterial growth. SEM identified widespread adsorption of host fouling across the test dressings which occurred prior to microbial binding. Therein, microbial attachment occurred predominantly to host fouling and not directly to the dressings. Bacterial binding is not unique to dialkylcarbamoyl chloride (DACC) dressings and under clinically relevant in vitro conditions and in vivo observations, we demonstrate (in addition to previously published work) that the bacterial binding capabilities are not effective at reducing the number of bacteria in laboratory models or human wounds.

Bioresponsive gingerol-loaded alginate-coated niosomal nanoparticles for targeting intracellular bacteria and cancer cells

Targeting and treating intracellular pathogen infections has been long-standing challenge, particularly in light of the escalating prevalence of antimicrobial resistance. Herein, an optimum formulation of alginate (AL)-coated niosome-based carriers for delivery of herbal extract Gingerol (Gin) was developed to treat intracellular pathogen infections and cancer cells. We used Gin-Nio@AL as a model drug to assess its efficacy against Gram-negative/positive bacteria and breast cancer cell lines. Our investigation affirmed its heightened antibacterial and anticancer properties. The antibacterial activity of Gin-Nio@AL against intracellular Staphylococcus aureus (S. aureus) and pseudomonas aeruginosa (P. aeruginosa) was also tested. In the current study, the niosome nanoparticles containing herbal extract Gingerol were optimized regarding lipid content and Surfactant per Cholesterol molar ratio. The developed formulation provided potential advantages, such as smooth globular surface morphology, small diameter (240.68 nm), pH-sensitive sustained release, and high entrapment efficiency (94.85 %). The release rate of Gin from AL-coated niosomes (Gin-Nio@AL) in physiological and acidic pH is lower than uncoated nanoparticles (Gin-Nio). Besides, the release rate of Gin from niosomal formulations increased in acidic pH. The Gin-Nio@AL demonstrated good antimicrobial activity against S. aureus and P. aeruginosa, and compared to Gin-Nio, the MIC values decreased to 7.82 ± 0.00 and 1.95 ± 0.00 μg/mL, respectively. In addition, the time-kill assay results showed that the developed formulation significantly reduced the number of bacteria in both strains compared to other tested groups. The microtiter data and scanning electron microscope micrography showed that Gin-Nio@AL has a more significant inhibitory effect on biofilm formation than Gin-Nio and Gin. The cell cytotoxicity evaluation showed that Gin-Nio@AL reduced the survival rate of MDA-MB-231 cancer cells to 52.4 % and 45.2 % after 48 h and 72 h, respectively. The elimination of intracellular pathogens was investigated through a breast cancer cell infection in an in vitro model. Gin-Nio@AL exhibited an enhanced and sustained intracellular antibacterial activity against pathogens-infected breast cancer cells compared to other tested formulations. Overall, Gin-Nio@AL enables the triggered release and targeting of intra-extra cellular bacteria and cancer cells and provides a novel and promising candidate for treating intracellular pathogen infections and cancer cells.

Trends in Anti-Tumor Effects of Pseudomonas aeruginosa Mannose-Sensitive-Hemagglutinin (PA-MSHA): An Overview of Positive and Negative Effects

Cancer is a leading cause of death worldwide, for which finding the optimal therapy remains an ongoing challenge. Drug resistance, toxic side effects, and a lack of specificity pose significant difficulties in traditional cancer treatments, leading to suboptimal clinical outcomes and high mortality rates among cancer patients. The need for alternative therapies is crucial, especially for those resistant to conventional methods like chemotherapy and radiotherapy or for patients where surgery is not possible. Over the past decade, a novel approach known as bacteria-mediated cancer therapy has emerged, offering potential solutions to the limitations of conventional treatments. An increasing number of in vitro and in vivo studies suggest that the subtype of highly virulent Pseudomonas aeruginosa bacterium called Pseudomonas aeruginosa mannose-sensitive-hemagglutinin (PA-MSHA) can successfully inhibit the progression of various cancer types, such as breast, lung, and bladder cancer, as well as hepatocellular carcinoma. PA-MSHA inhibits the growth and proliferation of tumor cells and induces their apoptosis. Proposed mechanisms of action include cell-cycle arrest and activation of pro-apoptotic pathways regulated by caspase-9 and caspase-3. Moreover, clinical studies have shown that PA-MSHA improved the effectiveness of chemotherapy and promoted the activation of the immune response in cancer patients without causing severe side effects. Reported adverse reactions were fever, skin irritation, and pain, attributed to the overactivation of the immune response. This review aims to summarize the current knowledge obtained from in vitro, in vivo, and clinical studies available at PubMed, Google Scholar, and ClinicalTrials.gov regarding the use of PA-MSHA in cancer treatment in order to further elucidate its pharmacological and toxicological properties.

In vivo evolution of antimicrobial resistance in a biofilm model of Pseudomonas aeruginosa lung infection

The evolution of antimicrobial resistance (AMR) in biofilms has been repeatedly studied by experimental evolution in vitro, but rarely in vivo. The complex microenvironment at the infection site imposes selective pressures on the bacterial biofilms, potentially influencing the development of AMR. We report here the development of AMR in an in vivo mouse model of Pseudomonas aeruginosa biofilm lung infection. The P. aeruginosa embedded in seaweed alginate beads underwent four successive lung infection passages with or without ciprofloxacin (CIP) exposure. The development of CIP resistance was assessed at each passage by population analysis of the bacterial populations recovered from the lungs of CIP-treated and control mice, with subsequent whole-genome sequencing of selected isolates. As inflammation plays a crucial role in shaping the microenvironment at the infection site, its impact was explored through the measurement of cytokine levels in the lung homogenate. A rapid development of AMR was observed starting from the second passage in the CIP-treated mice. Genetic analysis revealed mutations in nfxB, efflux pumps (mexZ), and two-component systems (parS) contribution to CIP resistance. The control group isolates exhibited mutations in the dipA gene, likely associated with biofilm dispersion. In the initial two passages, the CIP-treated group exhibited an elevated inflammatory response compared to the control group. This increase may potentially contribute to the release of mutagenic reactive oxygen species and the development of AMR. In conclusion, this study illustrates the complex relationship between infection, antibiotic treatment, and immune response.

Restoring the epigenetic landscape of lung microbiome: potential therapeutic approach for chronic respiratory diseases

BACKGROUND

Chronic respiratory diseases, such as chronic obstructive pulmonary disease (COPD) and bronchiectasis, present significant threats to global health. Recent studies have revealed the crucial role of the lung microbiome in the development of these diseases. Pathogens have evolved complex strategies to evade the immune response, with the manipulation of host cellular epigenetic mechanisms playing a pivotal role. There is existing evidence regarding the effects of Pseudomonas on epigenetic modifications and their association with pulmonary diseases. Therefore, this study aims to directly assess the connection between Pseudomonas abundance and chronic respiratory diseases. We hope that our findings will shed light on the molecular mechanisms behind lung pathogen infections.

METHODS

We analyzed data from 366 participants, including individuals with COPD, acute exacerbations of COPD (AECOPD), bronchiectasis, and healthy individuals. Previous studies have given limited attention to the impact of Pseudomonas on these groups and their comparison with healthy individuals. Two independent datasets from different ethnic backgrounds were used for external validation. Each dataset separately analyzed bacteria at the genus level.

RESULTS

The study reveals that Pseudomonas, a bacterium, was consistently found in high concentrations in all chronic lung disease datasets but it was present in very low abundance in the healthy datasets. This suggests that Pseudomonas may influence cellular mechanisms through epigenetics, contributing to the development and progression of chronic respiratory diseases.

CONCLUSIONS

This study emphasizes the importance of understanding the relationship between the lung microbiome, epigenetics, and the onset of chronic pulmonary disease. Enhanced recognition of molecular mechanisms and the impact of the microbiome on cellular functions, along with a better understanding of these concepts, can lead to improved diagnosis and treatment.

Bacterial synergies and antagonisms affecting Pseudomonas aeruginosa virulence in the human lung, skin and intestine

Pseudomonas aeruginosa requires a significant breach in the host defense to cause an infection. While its virulence factors are well studied, its tropism cannot be explained only by studying its interaction with the host. Why are P. aeruginosa infections so rare in the intestine compared with the lung and skin? There is not enough evidence to claim specificity in virulence factors deployed by P. aeruginosa in each anatomical site, and host physiology differences between the lung and the intestine cannot easily explain the observed differences in virulence. This perspective highlights a relatively overlooked parameter in P. aeruginosa virulence, namely, potential synergies with bacteria found in the human skin and lung, as well as antagonisms with bacteria of the human intestine.

Therapeutic potential of Pseudomonas aeruginosa-mannose sensitive hemagglutinin (PA-MSHA) in cancer treatment

Pseudomonas aeruginosa is a Gram-negative bacteria and it has been demonstrated that immunization with the outer membrane proteins of the microbe produces most of the relevant human antibodies. The peritrichous P. aeruginosa strain with MSHA fimbriae (PA-MSHA strain) has been found to be effective in the inhibition of growth and proliferation of different types of cancer cells. Furthermore, it has been revealed that PA-MSHA exhibits cytotoxicity because of the presence of MSHA and therefore it possesses anti-carcinogenic ability against different types of human cancer cell lines including, gastric, breast, hepatocarcinoma and nasopharyngeal cells. Studies have revealed that PA-MSHA exhibits therapeutic potential against cancer growth by induction of apoptosis, arrest of cell cycle, activating NF-κB/TLR5 pathway, etc. In China, PA-MSHA injections have been approved for the treatment of malignant tumor patients from very long back. The present review article demonstrates the therapeutic potential of PA-MSHA against various types of human cancers and explains the underlying mechanism.

In-depth biological characterization of two black soldier fly anti-Pseudomonas peptides reveals LPS-binding and immunomodulating effects

As effector molecules of the innate immune system, antimicrobial peptides (AMPs) have gathered substantial interest as a potential future generation of antibiotics. Here, we demonstrate the anti-Pseudomonas activity and lipopolysaccharide (LPS)-binding ability of HC1 and HC10, two cecropin peptides from the black soldier fly (Hermetia Illucens). Both peptides are active against a wide range of Pseudomonas aeruginosa strains, including drug-resistant clinical isolates. Moreover, HC1 and HC10 can bind to lipid A, the toxic center of LPS and reduce the LPS-induced nitric oxide and cytokine production in murine macrophage cells. This suggests that the peptide-LPS binding can also lower the strong inflammatory response associated with P. aeruginosa infections. As the activity of AMPs is often influenced by the presence of salts, we studied the LPS-binding activity of HC1 and HC10 in physiological salt concentrations, revealing a strong decrease in activity. Our research confirmed the early potential of HC1 and HC10 as starting points for anti-Pseudomonas drugs, as well as the need for structural or formulation optimization before further preclinical development can be considered. IMPORTANCE The high mortality and morbidity associated with Pseudomonas aeruginosa infections remain an ongoing challenge in clinical practice that requires urgent action. P. aeruginosa mostly infects immunocompromised individuals, and its prevalence is especially high in urgent care hospital settings. Lipopolysaccharides (LPSs) are outer membrane structures that are responsible for inducing the innate immune cascade upon infection. P. aeruginosa LPS can cause local excessive inflammation, or spread systemically throughout the body, leading to multi-organ failure and septic shock. As antimicrobial resistance rates in P. aeruginosa infections are rising, the research and development of new antimicrobial agents remain indispensable. Especially, antimicrobials that can both kill the bacteria themselves and neutralize their toxins are of great interest in P. aeruginosa research to develop as the next generation of drugs.

Experimental evolution of Pseudomonas aeruginosa to colistin in spatially confined microdroplets identifies evolutionary trajectories consistent with adaptation in microaerobic lung environments

Antibiotic resistance is a continuing global health crisis. Identifying the evolutionary trajectories leading to increased antimicrobial resistance can be critical to the discovery of biomarkers for clinical diagnostics and new targets for drug discovery. While the combination of patient data and in vitro experimental evolution has been remarkably successful in extending our understanding of antimicrobial resistance, it can be difficult for in vitro methods to recapitulate the spatial structure and consequent microenvironments that characterize in vivo infection. Notably, in cystic fibrosis (CF) patients, changes to either the PmrA/PmrB or PhoP/PhoQ two-component systems have been identified as critical drivers for high levels of colistin and polymyxin resistance. When using microfluidic emulsions to provide spatially structured, low-competition environments, we found that adaptive mutations to phoQ were more successful than pmrB in increasing colistin resistance. Conversely, mutations to pmrB were readily identified using well-mixed unstructured cultures. We found that oxygen concentration gradients within the microdroplet emulsions favored adaptive changes to the PhoP/PhoQ pathway consistent with microaerobic conditions that can be found in the lungs of CF patients. We also observed mutations linked to hallmark adaptations to the CF lung environment, such as loss of motility and loss of O antigen biosynthesis (wbpL). Mutation to wbpL, in addition to causing loss of O antigen, was additionally shown to confer moderately increased colistin resistance. Taken together, our data suggest that distinct evolutionary trajectories to colistin resistance may be shaped by the microaerobic partitioning and spatial separation imposed within the CF lung.IMPORTANCEAntibiotic resistance remains one of the great challenges confronting public health in the world today. Individuals with compromised immune systems or underlying health conditions are often at an increased for bacterial infections. Patients with cystic fibrosis (CF) produce thick mucus that clogs airways and provides a very favorable environment for infection by bacteria that further decrease lung function and, ultimately, mortality. CF patients are often infected by bacteria such as Pseudomonas aeruginosa early in life and experience a series of chronic infections that, over time, become increasingly difficult to treat due to increased antibiotic resistance. Colistin is a major antibiotic used to treat CF patients. Clinical and laboratory studies have identified PmrA/PmrB and PhoP/PhoQ as responsible for increased resistance to colistin. Both have been identified in CF patient lungs, but why, in some cases, is it one and not the other? In this study, we show that distinct evolutionary trajectories to colistin resistance may be favored by the microaerobic partitioning found within the damaged CF lung.

Cytotoxic rhamnolipid micelles drive acute virulence in Pseudomonas aeruginosa

Pseudomonas aeruginosa is an opportunistic human pathogen that has developed multi- or even pan-drug resistance towards most frontline and last resort antibiotics, leading to increasing infections and deaths among hospitalized patients, especially those with compromised immune systems. Further complicating treatment, P. aeruginosa produces numerous virulence factors that contribute to host tissue damage and immune evasion, promoting bacterial colonization and pathogenesis. In this study, we demonstrate the importance of rhamnolipid production in host-pathogen interactions. Secreted rhamnolipids form micelles that exhibited highly acute toxicity towards murine macrophages, rupturing the plasma membrane and causing organellar membrane damage within minutes of exposure. While rhamnolipid micelles (RMs) were particularly toxic to macrophages, they also caused membrane damage in human lung epithelial cells, red blood cells, Gram-positive bacteria, and even non-cellular models like giant plasma membrane vesicles. Most importantly, rhamnolipid production strongly correlated to P. aeruginosa virulence against murine macrophages in various panels of clinical isolates. Altogether, our findings suggest that rhamnolipid micelles are highly cytotoxic virulence factors that drive acute cellular damage and immune evasion during P. aeruginosa infections.

Model-driven characterization of functional diversity of Pseudomonas aeruginosa clinical isolates with broadly representative phenotypes

Pseudomonas aeruginosa is a leading cause of infections in immunocompromised individuals and in healthcare settings. This study aims to understand the relationships between phenotypic diversity and the functional metabolic landscape of P. aeruginosa clinical isolates. To better understand the metabolic repertoire of P. aeruginosa in infection, we deeply profiled a representative set from a library of 971 clinical P. aeruginosa isolates with corresponding patient metadata and bacterial phenotypes. The genotypic clustering based on whole-genome sequencing of the isolates, multi-locus sequence types, and the phenotypic clustering generated from a multi-parametric analysis were compared to each other to assess the genotype-phenotype correlation. Genome-scale metabolic network reconstructions were developed for each isolate through amendments to an existing PA14 network reconstruction. These network reconstructions show diverse metabolic functionalities and enhance the collective P. aeruginosa pangenome metabolic repertoire. Characterizing this rich set of clinical P. aeruginosa isolates allows for a deeper understanding of the genotypic and metabolic diversity of the pathogen in a clinical setting and lays a foundation for further investigation of the metabolic landscape of this pathogen and host-associated metabolic differences during infection.

Ketogenesis promotes tolerance to Pseudomonas aeruginosa pulmonary infection

Pseudomonas aeruginosa is a common cause of pulmonary infection. As a Gram-negative pathogen, it can initiate a brisk and highly destructive inflammatory response; however, most hosts become tolerant to the bacterial burden, developing chronic infection. Using a murine model of pneumonia, we demonstrate that this shift from inflammation to disease tolerance is promoted by ketogenesis. In response to pulmonary infection, ketone bodies are generated in the liver and circulate to the lungs where they impose selection for P. aeruginosa strains unable to display surface lipopolysaccharide (LPS). Such keto-adapted LPS strains fail to activate glycolysis and tissue-damaging cytokines and, instead, facilitate mitochondrial catabolism of fats and oxidative phosphorylation (OXPHOS), which maintains airway homeostasis. Within the lung, P. aeruginosa exploits the host immunometabolite itaconate to further stimulate ketogenesis. This environment enables host-P. aeruginosa coexistence, supporting both pathoadaptive changes in the bacteria and the maintenance of respiratory integrity via OXPHOS.

Using model systems to unravel host-Pseudomonas aeruginosa interactions

Using model systems in infection biology has led to the discoveries of many pathogen-encoded virulence factors and critical host immune factors to fight pathogenic infections. Studies of the remarkable Pseudomonas aeruginosa bacterium that infects and causes disease in hosts as divergent as humans and plants afford unique opportunities to shed new light on virulence strategies and host defence mechanisms. One of the rationales for using model systems as a discovery tool to characterise bacterial factors driving human infection outcomes is that many P. aeruginosa virulence factors are required for pathogenesis in diverse different hosts. On the other side, many host signalling components, such as the evolutionarily conserved mitogen-activated protein kinases, are involved in immune signalling in a diverse range of hosts. Some model organisms that have less complex immune systems also allow dissection of the direct impacts of innate immunity on host defence without the interference of adaptive immunity. In this review, we start with discussing the occurrence of P. aeruginosa in the environment and the ability of this bacterium to cause disease in various hosts as a natural opportunistic pathogen. We then summarise the use of some model systems to study host defence and P. aeruginosa virulence.

Habitat Transition in the Evolution of Bacteria and Archaea

Related groups of microbes are widely distributed across Earth's habitats, implying numerous dispersal and adaptation events over evolutionary time. However, relatively little is known about the characteristics and mechanisms of these habitat transitions, particularly for populations that reside in animal microbiomes. Here, we review the literature concerning habitat transitions among a variety of bacterial and archaeal lineages, considering the frequency of migration events, potential environmental barriers, and mechanisms of adaptation to new physicochemical conditions, including the modification of protein inventories and other genomic characteristics. Cells dependent on microbial hosts, particularly bacteria from the Candidate Phyla Radiation, have undergone repeated habitat transitions from environmental sources into animal microbiomes. We compare their trajectories to those of both free-living cells-including the Melainabacteria, Elusimicrobia, and methanogenic archaea-and cellular endosymbionts and bacteriophages, which have made similar transitions. We conclude by highlighting major related topics that may be worthy of future study.

Spatial lipidomics reveals biased phospholipid remodeling in acute Pseudomonas lung infection

Pseudomonas aeruginosa (Pa) is a pathogen causing chronic pulmonary infections in patients with cystic fibrosis (CF). Manipulation of lipids is an important feature of Pa infection and on a tissue-level scale is poorly understood. Using a mouse model of acute Pa pulmonary infection, we explored the whole-lung phospholipid response using mass spectrometry imaging (MSI) and spatial lipidomics. Using a histology-driven analysis, we isolated airways and parenchyma from both mock- and Pa-infected lungs and used systems biology tools to identify enriched metabolic pathways from the differential phospholipid identities. Infection was associated with a set of 26 ions, with 11 unique to parenchyma and 6 unique to airways. Acyl remodeling was differentially enriched in infected parenchyma as the predominant biological function. These functions correlated with markers of polymorphonuclear (PMN) cell influx, a defining feature of the lung response to Pa infection, implicating enzymes active in phospholipid remodeling.

Bacterial Chitinases and Their Role in Human Infection

It has been widely appreciated that numerous bacterial species express chitinases for the purpose of degrading environmental chitin. However, chitinases and chitin-binding proteins are also expressed by pathogenic bacterial species during infection even though mammals do not produce chitin. Alternative molecular targets are therefore likely present within the host. Here, we will describe our current understanding of chitinase/chitin-binding proteins as virulence factors that promote bacterial colonization and infection. The targets of these chitinases in the host have been shown to include immune system components, mucins, and surface glycans. Bacterial chitinases have also been shown to interact with other microorganisms, targeting the peptidoglycan or chitin in the bacterial and fungal cell wall, respectively. This review highlights that even though the name "chitinase" implies activity toward chitin, chitinases can have a wide diversity of targets, including ones relevant to host infection. Chitinases may therefore be useful as a target of future anti-infective therapeutics.

AMPK activation improves recovery from pneumonia-induced lung injury via reduction of er-stress and apoptosis in alveolar epithelial cells

BACKGROUND

Bacterial pneumonia and related lung injury are among the most frequent causes of mortality in intensive care units, but also inflict serious and prolonged respiratory complications among survivors. Given that endoplasmic reticulum (ER) stress is a hallmark of sepsis-related alveolar epithelial cell (AEC) dysfunction, we tested if AMP-activated protein kinase (AMPK) affects recovery from ER stress and apoptosis of AECs during post-bacterial infection.

METHODS

In a murine model of lung injury by P. aeruginosa non-lethal infection, therapeutic interventions included AMPK activator metformin or GSK-3β inhibitor Tideglusib for 96 h. Recovery from AEC injury was evidenced by accumulation of soluble T-1α (AEC Type 1 marker) in BAL fluids along with fluorescence analysis of ER-stress (CHOP) and apoptosis (TUNEL) in lung sections. AMPK phosphorylation status and mediators of ER stress were determined via Immunoblot analysis from lung homogenates. Macrophage-dependent clearance of apoptotic cells was determined using flow cytometry assay.

RESULTS

P. aeruginosa-induced lung injury resulted in accumulation of neutrophils and cellular debris in the alveolar space along with persistent (96 h) ER-stress and apoptosis of AECs. While lung infection triggered AMPK inactivation (de-phosphorylation of Thr172-AMPK), metformin and Tideglusib promptly restored the AMPK activation status. In post infected mice, AMPK activation reduced indices of lung injury, ER stress and related apoptosis of AECs, as early as 24 h post administration of AMPK activators. In addition, we demonstrate that the extent of apoptotic cell accumulation is also dependent on AMPK-mediated clearance of apoptotic cells by macrophages.

CONCLUSIONS

Our study provides important insights into AMPK function in the preservation of AEC viability after bacterial infection, in particular due reduction of ER-stress and apoptosis, thereby promoting effective recovery from lung injury after pneumonia.

Exploring the 'N-terminal arm' & 'Convex surface' binding Interfaces of the T3SS Chaperone-Translocator Complexes from P. aeruginosa

One infection method widely used by many gram-negative bacteria involves a protein nanomachine called the Type Three Secretion System (T3SS). The T3SS enables the transportation of bacterial "toxins" via a proteinaceous channel that directly links the cytosol of the bacteria and host cell. The channel from the bacteria is completed by a translocon pore formed by two proteins named the major and minor translocators. Prior to pore formation, the translocator proteins are bound to a small chaperone within the bacterial cytoplasm. This interaction is crucial to effective secretion. Here we investigated the specificity of the binding interfaces of the translocator-chaperone complexes from Pseudomonas aeruginosa via the selection of peptide and protein libraries based on its chaperone PcrH. Five libraries encompassing PcrH's N-terminal and central α-helices were panned, using ribosome display, against both the major (PopB) and minor (PopD) translocator. Both translocators were shown to significantly enrich a similar pattern of WT and non-WT sequences from the libraries. This highlighted key similarities/differences between the interactions of the major and minor translocators with their chaperone. Moreover, as the enriched non-WT sequences were specific to each translocator, it would suggest that PcrH can be adapted to bind each translocator individually. The ability to evolve such proteins indicates that these molecules may provide promising anti-bacterial candidates.

Exploring the "N-Terminal Anchor" Binding Interface of the T3SS Chaperone-Translocator Complexes from P. aeruginosa

The type III secretion system is a large multiprotein complex that many Gram-negative bacteria use for infection. A crucial part of the complex is its translocon pore formed by two proteins: the major and minor translocators. The pore completes a proteinaceous channel from the bacterial cytosol through the host cell membrane and allows the direct injection of bacterial toxins. Effective pore formation is predicated by the translocator proteins binding to a small chaperone within the bacterial cytoplasm. Given the vital role of the chaperone-translocator interaction, we investigated the specificity of the "N-terminal anchor" binding interface present in both translocator-chaperone complexes from Pseudomonas aeruginosa. Isothermal calorimetry (ITC), alanine scanning, and the selection of a motif-based peptide library using ribosome display were used to characterize the major (PopB) and minor (PopD) translocator interactions with their chaperone PcrH. We show that 10 mer PopB_51-60 and PopD_47-56 peptides bind to PcrH with a K_D of 148 ± 18 and 91 ± 9 μM, respectively. Moreover, mutation to alanine of each of the consensus residues (xxVxLxxPxx) of the PopB peptide severely affected or completely abrogated binding to PcrH. When the directed peptide library (X-X-hydrophobic-X-L-X-X-P-X-X) was panned against PcrH, there was no obvious convergence at the varied residues. The PopB/PopD wild-type (WT) sequences were also not prevalent. However, a consensus peptide was shown to bind to PcrH with micromolar affinity. Thus, selected sequences were binding with similar affinities to WT PopB/PopD peptides. These results demonstrate that only the conserved "xxLxxP" motif drives binding at this interface.

Immune escape strategies of Pseudomonas aeruginosa to establish chronic infection

The infection caused by P. aeruginosa still is dangerous throughout the world. This is partly due to its immune escape mechanisms considerably increasing the bacterial survival in the host. By escape from recognition by TLRs, interference with complement system activation, phagocytosis inhibition, production of ROS, inhibition of NET production, interference with the generation of cytokines, inflammasome inhibition, reduced antigen presentation, interference with cellular and humoral immunity, and induction of apoptotic cell death and MDSc, P. aeruginosa breaks down the barriers of the immune system and causes lethal infections in the host. Recognition of other immune escape mechanisms of P. aeruginosa may provide a basis for the future treatment of the infection. This manuscript may provide new insights and information for the development of new strategies to combat P. aeruginosa infection. In the present manuscript, the escape mechanisms of P. aeruginosa against immune response would be reviewed.

Functional Amyloids in Pseudomonas aeruginosa Are Essential for the Proteome Modulation That Leads to Pathoadaptation in Pulmonary Niches

Persistence and survival of Pseudomonas aeruginosa in chronic lung infections is closely linked to the biofilm lifestyle. One biofilm component, functional amyloid of P. aeruginosa (Fap), imparts structural adaptations for biofilms; however, the role of Fap in pathogenesis is still unclear. Conservation of the fap operon encoding Fap and P. aeruginosa being an opportunistic pathogen of lung infections prompted us to explore its role in lung infection. We found that Fap is essential for establishment of lung infection in rats, as its genetic exclusion led to mild focal infection with quick resolution. Moreover, without an underlying cystic fibrosis (CF) genetic disorder, overexpression of Fap reproduced the CF pathotype. The molecular basis of Fap-mediated pulmonary adaptation was explored through surface-associated proteomics in vitro. Differential proteomics positively associated Fap expression with activation of known proteins related to pulmonary pathoadaptation, attachment, and biofilm fitness. The aggregative bacterial phenotype in the pulmonary niche correlated with Fap-influenced activation of biofilm sustainability regulators and stress response regulators that favored persistence-mediated establishment of pulmonary infection. Fap overexpression upregulated proteins that are abundant in the proteome of P. aeruginosa in colonizing CF lungs. Planktonic lifestyle, defects in anaerobic pathway, and neutrophilic evasion were key factors in the absence of Fap that impaired establishment of infection. We concluded that Fap is essential for cellular equilibration to establish pulmonary infection. Amyloid-induced bacterial aggregation subverted the immune response, leading to chronic infection by collaterally damaging tissue and reinforcing bacterial persistence. IMPORTANCE Pseudomonas aeruginosa is inextricably linked with chronic lung infections. In this study, the well-conserved Fap operon was found to be essential for pathoadaptation in pulmonary infection in a rat lung model. Moreover, the presence of Fap increased pathogenesis and biofilm sustainability by modulating bacterial physiology. Hence, a pathoadaptive role of Fap in pulmonary infections can be exploited for clinical application by targeting amyloids. Furthermore, genetic conservation and extracellular exposure of Fap make it a commendable target for such interventions.

Ultrasound-responsive catalytic microbubbles enhance biofilm elimination and immune activation to treat chronic lung infections

Efficient treatment of chronic lung infections caused by Pseudomonas aeruginosa biofilms is a great challenge because of drug tolerance and immune evasion issues. Here, we develop ultrasound-responsive catalytic microbubbles with biofilm elimination and immune activation properties to combat chronic lung infection induced by P. aeruginosa biofilms. In these microbubbles, piperacillin and Fe₃O₄ nanoparticles form a drug-loaded shell surrounding the air core. Under ultrasound stimulation, the microbubbles can physically disrupt the structure of biofilms and enhance the penetration of both Fe₃O₄ nanoparticles and piperacillin into the biofilm. Then, Fe₃O₄ nanoparticles chemically degrade the biofilm matrix and kill the bacteria with the assistance of piperacillin. Fe₃O₄ nanoparticles can activate the immune response for biofilm elimination by polarizing macrophages into a pro-inflammatory phenotype. These ultrasound-responsive catalytic microbubbles efficiently treat chronic lung infections in a mouse model by combining physical/chemical/antibiotic biofilm elimination and immune activation, thus providing a promising strategy for combating bacterial biofilm infections.

Opposites Attract: Electrostatically Driven Loading of Antimicrobial Peptides into Phytoglycogen Nanocarriers

Antimicrobial peptides, such as GL13K, have a high binding selectivity toward bacterial membranes, while not affecting healthy mammalian cells at therapeutic concentrations. However, delivery of these peptides is challenging since they are susceptible to proteolytic hydrolysis and exhibit poor cellular uptake. A protective nanocarrier is thus proposed to overcome these obstacles. We investigate the potential to employ biodegradable phytoglycogen nanoparticles as carriers for GL13K using a simple loading protocol based on electrostatic association rather than chemical conjugation, eliminating the need for control of chemical cleavage for release of the peptide in situ. Both the native (quasi-neutral) and carboxymethylated (anionic) phytoglycogen were evaluated for their colloidal stability, loading capacity, and release characteristics. We show that the anionic nanophytoglycogen carries a greater cationic GL13K load and exhibits slower release kinetics than native nanophytoglycogen. Isotope exchange measurements demonstrate that the antimicrobial peptide is entrapped in the pores of the dendritic-like macromolecule, which should provide the necessary protection for delivery. Importantly, the nanoformulations are active against a Pseudomonas aeruginosa clinical isolate at concentrations comparable to those of the free peptide and representative, small molecule antibiotics. The colloidal nanocarrier preserves peptide stability and antimicrobial activity, even after long periods of storage (at least 8 months).

An Isolate of Streptococcus mitis Displayed In Vitro Antimicrobial Activity and Deleterious Effect in a Preclinical Model of Lung Infection

Microbiota studies have dramatically increased over these last two decades, and the repertoire of microorganisms with potential health benefits has been considerably enlarged. The development of next generation probiotics from new bacterial candidates is a long-term strategy that may be more efficient and rapid with discriminative in vitro tests. Streptococcus strains have received attention regarding their antimicrobial potential against pathogens of the upper and, more recently, the lower respiratory tracts. Pathogenic bacterial strains, such as non-typable Haemophilus influenzae (NTHi), Pseudomonas aeruginosa (P. aeruginosa) and Staphylococcus aureus (S. aureus), are commonly associated with acute and chronic respiratory diseases, and it could be interesting to fight against pathogens with probiotics. In this study, we show that a Streptococcus mitis (S. mitis) EM-371 strain, isolated from the buccal cavity of a human newborn and previously selected for promising anti-inflammatory effects, displayed in vitro antimicrobial activity against NTHi, P. aeruginosa or S. aureus. However, the anti-pathogenic in vitro activity was not sufficient to predict an efficient protective effect in a preclinical model. Two weeks of treatment with S. mitis EM-371 did not protect against, and even exacerbated, NTHi lung infection.

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.

Overcoming Barriers to Preventing and Treating P. aeruginosa Infections Using AAV Vectored Immunoprophylaxis

Pseudomonas aeruginosa is a bacterial pathogen of global concern and is responsible for 10-15% of nosocomial infections worldwide. This opportunistic bacterial pathogen is known to cause serious complications in immunocompromised patients and is notably the leading cause of morbidity and mortality in patients suffering from cystic fibrosis. Currently, the only line of defense against P. aeruginosa infections is antibiotic treatment. Due to the acquired and adaptive resistance mechanisms of this pathogen, the prevalence of multidrug resistant P. aeruginosa strains has increased, presenting a major problem in healthcare settings. To date, there are no approved licensed vaccines to protect against P. aeruginosa infections, prompting the urgent need alternative treatment options. An alternative to traditional vaccines is vectored immunoprophylaxis (VIP), which utilizes a safe and effective adeno-associated virus (AAV) gene therapy vector to produce sustained levels of therapeutic monoclonal antibodies (mAbs) in vivo from a single intramuscular injection. In this review, we will provide an overview of P. aeruginosa biology and key mechanisms of pathogenesis, discuss current and emerging treatment strategies for P. aeruginosa infections and highlight AAV-VIP as a promising novel therapeutic platform.

A truncated mutation of MucA in Pseudomonas aeruginosa from a bronchiectasis patient affects T3SS expression and inflammasome activation

Pseudomonas aeruginosa is an opportunistic pathogen that causes chronic airway infection in bronchiectasis patients and is closely associated with poor prognosis. Strains isolated from chronically infected patients typically have a mucoid phenotype due to the overproduction of alginate. In this study, we isolate a P. aeruginosa strain from the sputum of a patient with bronchiectasis and find that a truncated mutation occurred in mucA, which is named mucA117. mucA117 causes the strain to transform into a mucoid phenotype, downregulates the expression of T3SS and inflammasome ligands such as fliC and allows it to avoid inflammasome activation. The truncated mutation of the MucA protein may help P. aeruginosa escape clearance by the immune system, enabling long-term colonization.

Bacterial chemotaxis in human diseases

To infect and cause disease, bacterial pathogens must localize to specific regions of the host where they possess the metabolic and defensive acumen for survival. Motile flagellated pathogens exercise control over their localization through chemotaxis to direct motility based on the landscape of exogenous nutrients, toxins, and molecular cues sensed within the host. Here, we review advances in understanding the roles chemotaxis plays in human diseases. Chemotaxis drives pathogen colonization to sites of inflammation and injury and mediates fitness advantages through accessing host-derived nutrients from damaged tissue. Injury tropism may worsen clinical outcomes through instigating chronic inflammation and subsequent cancer development. Inhibiting bacterial chemotactic systems could act synergistically with antibacterial medicines for more effective and specific eradication.

Inhibition of Pseudomonas aeruginosa LPS-Induced airway inflammation by RIPK3 in human airway

Although the physiological function of receptor-interacting protein kinase (RIPK) 3 has emerged as a critical mediator of programmed necrosis/necroptosis, the intracellular role it plays as an attenuator in human lungs and human bronchial epithelia remains unclear. Here, we show that the expression of RIPK3 dramatically decreased in the inflamed tissues of human lungs, and moved from the nucleus to the cytoplasm. The overexpression of RIPK3 dramatically increased F-actin formation and decreased the expression of genes for pro-inflammatory cytokines (IL-6 and IL-1β), but not siRNA-RIPK3. Interestingly, whereas RIPK3 was bound to histone 1b without LPS stimulation, the interaction between them was disrupted after 15 min of LPS treatment. Histone methylation could not maintain the binding of RIPK3 and activated movement towards the cytoplasm. In the cytoplasm, overexpressed RIPK3 continuously attenuated pro-inflammatory cytokine gene expression by inhibiting NF-κB activation, preventing the progression of inflammation during Pseudomonas aeruginosa infection. Our data indicated that RIPK3 is critical for the regulation of the LPS-induced inflammatory microenvironment. Therefore, we suggest that RIPK3 is a potential therapeutic candidate for bacterial infection-induced pulmonary inflammation.

High-Level Expression of Cell-Surface Signaling System Hxu Enhances Pseudomonas aeruginosa Bloodstream Infection

Bloodstream infections (BSIs) caused by Pseudomonas aeruginosa are associated with a high mortality rate in the clinic. However, the fitness mechanisms responsible for the evolution of virulence factors that facilitate the dissemination of P. aeruginosa to the bloodstream are poorly understood. In this study, a transcriptomic analysis of the BSI-associated P. aeruginosa clinical isolates showed a high-level expression of cell-surface signaling (CSS) system Hxu. Whole-genome sequencing and comparative genomics of these isolates showed that a mutation in rnfE gene was responsible for the elevated expression of the Hxu-CSS pathway. Most importantly, deletion of the hxuIRA gene cluster in a laboratory strain PAO1 reduced its BSI capability while overexpression of the HxuIRA pathway promoted BSI in a murine sepsis model. We further demonstrated that multiple components in the blood plasma, including heme, hemoglobin, the heme-scavenging proteins haptoglobin, and hemopexin, as well as the iron-delivery protein transferrin, could activate the Hxu system. Together, these studies suggested that the Hxu-CSS system was an important signal transduction pathway contributing to the adaptive pathogenesis of P. aeruginosa in BSI.

Conquering the host: Bordetella spp. and Pseudomonas aeruginosa molecular regulators in lung infection

When bacteria sense cues from the host environment, stress responses are activated. Two component systems, sigma factors, small RNAs, ppGpp stringent response, and chaperones start coordinate the expression of virulence factors or immunomodulators to allow bacteria to respond. Although, some of these are well studied, such as the two-component systems, the contribution of other regulators, such as sigma factors or ppGpp, is increasingly gaining attention. Pseudomonas aeruginosa is the gold standard pathogen for studying the molecular mechanisms to sense and respond to environmental cues. Bordetella spp., on the other hand, is a microbial model for studying host-pathogen interactions at the molecular level. These two pathogens have the ability to colonize the lungs of patients with chronic diseases, suggesting that they have the potential to share a niche and interact. However, the molecular networks that facilitate adaptation of Bordetella spp. to cues are unclear. Here, we offer a side-by-side comparison of what is known about these diverse molecular mechanisms that bacteria utilize to counteract host immune responses, while highlighting the relatively unexplored interactions between them.

An Immunochemical Approach to Detect the Quorum Sensing-Regulated Virulence Factor 2-Heptyl-4-Quinoline N-Oxide (HQNO) Produced by Pseudomonas aeruginosa Clinical Isolates

Understanding quorum sensing (QS) and its role in the development of pathogenesis may provide new avenues for diagnosing, surveillance, and treatment of infectious diseases. For this purpose, the availability of reliable and efficient analytical diagnostic tools suitable to specifically detect and quantify these essential QS small molecules and QS regulated virulence factors is crucial. Here, we reported the development and evaluation of antibodies and an enzyme-linked immunosorbent assay (ELISA) for HQNO (2-heptyl-4-quinoline N-oxide), a QS product of the PqsR system, which has been found to act as a major virulence factor that interferes with the growth of other microorganisms. Despite the nonimmunogenic character of HQNO, the antibodies produced showed high avidity and the microplate-based ELISA developed could detect HQNO in the low nM range. Hence, a limit of detection (LOD) of 0.60 ± 0.13 nM had been reached in Müeller Hinton (MH) broth, which was below previously reported levels using sophisticated equipment based on liquid chromatography coupled to mass spectrometry. The HQNO profile of release of different Pseudomonas aeruginosa clinical isolates analyzed using this ELISA showed significant differences depending on whether the clinical isolates belonged to patients with acute or chronic infections. These data point to the possibility of using HQNO as a specific biomarker to diagnose P. aeruginosa infections and for patient surveillance. Considering the role of HQNO in inhibiting the growth of coinfecting bacteria, the present ELISA will allow the investigation of these complex bacterial interactions underlying infections. IMPORTANCE Bacteria use quorum sensing (QS) as a communication mechanism that releases small signaling molecules which allow synchronizing a series of activities involved in the pathogenesis, such as the biosynthesis of virulence factors or the regulation of growth of other bacterial species. HQNO is a metabolite of the Pseudomonas aeruginosa-specific QS signaling molecule PQS (Pseudomonas quinolone signal). In this work, the development of highly specific antibodies and an immunochemical diagnostic technology (ELISA) for the detection and quantification of HQNO was reported. The ELISA allowed profiling of the release of HQNO by clinical bacterial isolates, showing its potential value for diagnosing and surveillance of P. aeruginosa infections. Moreover, the antibodies and the ELISA reported here may contribute to the knowledge of other underlying conditions related to the pathology, such as the role of the interactions with other bacteria of a particular microbiota environment.

Immune Response to Biofilm Growing Pulmonary Pseudomonas aeruginosa Infection

Biofilm infections are tolerant to the host responses and recalcitrance to antibiotic drugs and disinfectants. The induced host-specific innate and adaptive immune responses by established biofilms are significantly implicated and contributes to the course of the infections. Essentially, the host response may be the single one factor impacting the outcome most, especially in cases where the biofilm is caused by low virulent opportunistic bacterial species. Due to the chronicity of biofilm infections, activation of the adaptive immune response mechanisms is frequently experienced, and instead of clearing the infection, the adaptive response adds to the pathogenesis. To a high degree, this has been reported for chronic Pseudomonas aeruginosa lung infections, where both a pronounced antibody response and a skewed Th1/Th2 balance has been related to a poorer outcome. In addition, detection of an adaptive immune response can be used as a significant indicator of a chronic P. aeruginosa lung infection and is included in the clinical definitions as such. Those issues are presented in the present review, along with a characterization of the airway structure in relation to immune responses towards P. aeruginosa pulmonary infections.

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.

Clinical Efficacy and In Vitro Drug Sensitivity Test Results of Azithromycin Combined With Other Antimicrobial Therapies in the Treatment of MDR P. aeruginosa Ventilator-Associated Pneumonia

Objective: The aim of the research was to study the effect of azithromycin (AZM) in the treatment of MDR P. aeruginosa VAP combined with other antimicrobial therapies.

Methods: The clinical outcomes were retrospectively collected and analyzed to elucidate the efficacy of different combinations involving azithromycin in the treatment of MDR-PA VAP. The minimal inhibitory concentration (MIC) of five drugs was measured by the agar dilution method against 27 isolates of MDR-PA, alone or in combination.

Results: The incidence of VAP has increased approximately to 10.4% (961/9245) in 5 years and 18.4% (177/961) caused by P. aeruginosa ranking fourth. A total of 151 cases of MDR P. aeruginosa were included in the clinical retrospective study. Clinical efficacy results are as follows: meropenem + azithromycin (MEM + AZM) was 69.2% (9/13), cefoperazone/sulbactam + azithromycin (SCF + AZM) was 60% (6/10), and the combination of three drugs containing AZM was 69.2% (9/13). The curative effect of meropenem + amikacin (MEM + AMK) was better than that of the meropenem + levofloxacin (MEM + LEV) group, p = 0.029 (p < 0.05). The curative effect of cefoperazone/sulbactam + amikacin (SCF + AMK) was better than that of the cefoperazone/sulbactam + levofloxacin (SCF + LEV) group, p = 0.025 (p < 0.05). There was no significant difference between combinations of two or three drugs containing AZM, p > 0.05 (p = 0.806). From the MIC results, the AMK single drug was already very sensitive to the selected strains. When MEM or SCF was combined with AZM, the sensitivity of them to strains can be significantly increased. When combined with MEM and AZM, the MIC₅₀ and MIC₉₀ of MEM decreased to 1 and 2 ug/mL from 8 to 32 ug/mL. When combined with SCF + AZM, the MIC₅₀ of SCF decreased to 16 ug/mL, and the curve shifted obviously. However, for the combination of SCF + LEV + AZM, MIC₅₀ and MIC₉₀ could not achieve substantive changes. From the FIC index results, the main actions of MEM + AZM were additive effects, accounting for 72%; for the combination of SCF + AZM, the additive effect was 40%. The combination of AMK or LEV with AZM mainly showed unrelated effects, and the combination of three drugs could not improve the positive correlation between LEV and AZM.

Conclusion: AZM may increase the effect of MEM or SCF against MDR P. aeruginosa VAP. Based on MEM or SCF combined with AMK or AZM, we can achieve a good effect in the treatment of MDR P. aeruginosa VAP.

Development of saline loaded mask materials, evaluation of the antimicrobial efficacy and survivability of selected bacteria on these mask materials

Objective

Surgical face masks have been recommended by World Health Organization (WHO) during the COVID-19 pandemic. Nowadays wearing masks have become a norm and lifestyle around the globe. The present investigation was carried out to evaluate the feasibility of developing masks loaded with analytical grade sodium chloride (NaCl), Iodized salts (IS) and Omani sea salt (OSS) with or without sodium bicarbonate (NaHCO₃).

Methods

The saline loaded masks were prepared by soaking the middle layer of the mask in 30% (w/v) saline solutions (NaCl, IS, OSS) with or without 10% NaHCO₃ for 24 h followed by drying at room temperature. The prepared saline solutions and its combinations were evaluated for antimicrobial efficacy against the bacteria like Escherichia coli, Pseudomonas aeruginosa, Proteus vulgaris, Salmonella typhi, and Staphylococcus aureus, and antifungal activity against the Penicillium spp. and Rhizopus spp. by agar diffusion. Optical microscopy was employed to observe the formation of salt crystal in the mask material. Survivability of S. aureus and P. aeruginosa was tested on the mask material loaded with 30% OSS + 10% NaHCO₃ at particular time intervals.

Results

The results showed that a combination of 30% OSS + 10% NaHCO₃ exhibited promising antimicrobial activity against all the bacteria as well as Rhizopus spp. compared to the 30% IS + 10% NaHCO₃. Moreover, the middle layer of the mask loaded with saline solutions of 30% OSS + 10% NaHCO₃ or 30% IS + 10% NaHCO₃ have antibacterial activity, particularly for oral microbiome. On dehydration, the masks materials showed the presence of a significant amount of salt crystals. Survivability tests showed that both S. aureus and P. aeruginosa were killed within 3 h of contact with the salt crystals on the mask materials.

Conclusions

A combination of 30% OSS + 10% NaHCO₃ possessed significant antimicrobial activities on the tested microorganisms. Presence of a significant amount of salt crystals on dehydration of the saline loaded masks can be used as an effective protective barrier to infectious respiratory agents.

Enzyme-Activated, Chemiluminescent Siderophore-Dioxetane Probes Enable the Selective and Highly Sensitive Detection of Bacterial Pathogens

The sensitive detection of bacterial infections is a prerequisite for their successful treatment. The use of a chemiluminescent readout was so far hampered by an insufficient probe enrichment at the pathogens. We coupled siderophore moieties, that harness the unique iron transport system of bacteria, with enzyme‐activatable dioxetanes and obtained seven trifunctional probes with high signal‐to‐background ratios (S/B=426‐859). Conjugates with efficient iron transport capability into bacteria were identified through a growth recovery assay. All ESKAPE pathogens were labelled brightly by desferrioxamine conjugates, while catechols were weaker due to self‐quenching. Bacteria could also be detected inside lung epithelial cells. The best probe 8 detected 9.1×10³ CFU mL⁻¹ of S. aureus and 5.0×10⁴ CFU mL⁻¹ of P. aeruginosa, while the analogous fluorescent probe 10 was 205–305fold less sensitive. This qualifies siderophore dioxetane probes for the selective and sensitive detection of bacteria.

Resistance Is Not Futile: The Role of Quorum Sensing Plasticity in Pseudomonas aeruginosa Infections and Its Link to Intrinsic Mechanisms of Antibiotic Resistance

Bacteria use a cell-cell communication process called quorum sensing (QS) to orchestrate collective behaviors. QS relies on the group-wide detection of extracellular signal molecules called autoinducers (AI). Quorum sensing is required for virulence and biofilm formation in the human pathogen Pseudomonas aeruginosa. In P. aeruginosa, LasR and RhlR are homologous LuxR-type soluble transcription factor receptors that bind their cognate AIs and activate the expression of genes encoding functions required for virulence and biofilm formation. While some bacterial signal transduction pathways follow a linear circuit, as phosphoryl groups are passed from one carrier protein to another ultimately resulting in up- or down-regulation of target genes, the QS system in P. aeruginosa is a dense network of receptors and regulators with interconnecting regulatory systems and outputs. Once activated, it is not understood how LasR and RhlR establish their signaling hierarchy, nor is it clear how these pathway connections are regulated, resulting in chronic infection. Here, we reviewed the mechanisms of QS progression as it relates to bacterial pathogenesis and antimicrobial resistance and tolerance.

Analysis of Microbiological and Clinical Characteristics of Bacterial Infection in Patients with Pulmonary Infection

Objective

Using data investigation, the microbiology of bacterial infection in patients with pulmonary infection was discussed, and its clinical characteristics were analyzed.

Methods

The clinical data of 160 patients with pulmonary infection in our hospital from March 2019 to March 2021 were collected and analyzed. Blood samples were collected and cultured, and the pathogens were identified. The distribution, constituent ratio, and drug resistance of pathogens in elderly patients with pulmonary infection were analyzed. Logistics regression analysis was adopted to analyze the risk factors of pulmonary infection.

Results

Of the 160 patients with pulmonary infection, 107 were males (66.88%) and 53 were females (33.13%). The age ranged from 12 to 97 years old, with an average of 63.82 ± 12.64 years old. Sevent-six patients (47.50%) were over 65 years old. Urban patients accounted for 71.88%, and rural patients accounted for 28.13%, of which workers accounted for 46.25%, and farmers and cadres each accounted for about 4%. 85.62% of smokers have smoked for more than 4 years. Eighty-five patients had chronic diseases such as coronary heart disease, hypertension, diabetes, and cerebrovascular disease. Heart failure occurred in 10.00%, old tuberculosis in 11.25%, and new tuberculosis in 5.63%. The average hospital stay of the patients was 14.93 days, and the improvement rate was 91.25%. Eleven patients died. Among the 160 patients with pulmonary infection, COPD, pneumonia, and lung cancer accounted for the highest proportions, and idiopathic pulmonary fibrosis, bronchitis dilatation, tuberculosis, and bronchial asthma also played an important role. Pathogenic bacteria were detected in 104 of the 160 elderly patients with pulmonary infection, and the detection rate was 65.00%. A total of 444 strains of pathogenic bacteria were detected, including 328 strains of Gram-negative bacteria (73.87%, mainly Klebsiella pneumoniae, Pseudomonas aeruginosa, Stenotrophomonas maltophilia, and Serratia marcescens), 28 strains of Gram-positive bacteria (6.30%, mainly Staphylococcus aureus), and 88 strains of fungi (20.00%, mainly Candida albicans). Regarding Klebsiella pneumoniae in elderly patients with pulmonary infection, the drug resistance rates were 59.72% for amoxicillin-clavulanate potassium, 52.78% for ampicillin sodium-sulbactam sodium, and 51.39% for cefazolin sodium. Regarding Pseudomonas aeruginosa, the drug resistance rates were 29.31% for ticarcillin sodium-potassium clavulanate, 27.59% for piperacillin sodium, and 24.14% for gentamicin. Regarding Stenotrophomonas maltophilia, the drug resistance rates were 79.55% for ceftazidime, 38.64% for chloramphenicol, and 31.82% for levofloxacin. Regarding Serratia marcescens, the drug resistance rates from high to low were 74.42% for cefotaxime, 72.09% for moxifloxacin, and 69.77% for gentamicin. Regarding Staphylococcus aureus in elderly patients with pulmonary infection, the drug resistance rates were 100.00% for penicillin, 61.54% for erythromycin, 61.54% for clarithromycin, and 61.54% for azithromycin. Regarding Candida albicans, the drug resistance rates from high to low were 22.41% for caspofungin, 15.52% for itraconazole, and 9.09% for fluconazole. The results of univariate analysis of pulmonary bacterial infection indicated that there were no significant differences in sex and body mass index between nonbacterial infection group and bacterial infection group (P > 0.05). There were significant differences in terms of dust or harmful gas exposure, family member smoking, chronic lung disease history, age, smoking, family cooking, hospital stay, and indwelling catheter (P < 0.05). Exposure to dust or harmful gases, family cooking, age, history of chronic lung disease, indwelling catheter, and length of hospital stay were risk factors for pulmonary bacterial infection (P < 0.05).

Conclusion

Gram-negative bacteria are the main pathogens in elderly patients with pulmonary infection. Antibiotics should be administered reasonably according to the results of the drug sensitivity test. Older age, history of chronic lung disease, catheter indwelling, and length of stay are the risk factors for pulmonary bacterial infection.

Hybrid N-Acylcysteines as Dual-Acting Matrix Disruptive and Anti-Quorum Sensing Agents Fighting Pseudomonas aeruginosa Biofilms: Design, Synthesis, Molecular Docking Studies, and In Vitro Assays

Biofilms facilitate the pathogenesis of life-threatening Pseudomonas aeruginosa infections by coating mucosal surfaces or invasive devices and offer protection from antimicrobial therapy and the host immune response, thus increasing mortality rates and financial burden. Herein, new hybrid N-acylcysteines (NAC) incorporating selected acyl groups from organic acids and their derivatives, which are capable of quenching pathogen quorum sensing (QS) systems, were designed and their antibiofilm activity and anti-QS were evaluated. N-acylcysteines (4a-h) were synthesized and characterized by ¹H NMR and ¹³C NMR, and their purity was confirmed by elemental analyses. N-(4-Hydroxy-3,5-dimethoxybenzoyl)-l-cysteine (4d) and N-(4-methoxybenzoyl)-l-cysteine (4h) showed a higher antibiofilm activity against PAO1 biofilms than the rest of the targets and the standard NAC. They showed 83 and 82% inhibition of biofilms at 5 mM and eradicated mature biofilms at 20 mM concentrations (NAC biofilm inhibition = 66% at 10 mM and minimum biofilm eradication concentration = 40 mM). This was confirmed via visualizing adherent biofilm cells on catheter pieces using scanning electron microscopy. In the same vein, both 4d and 4h showed the highest docking score with the QS signal receptor protein LasR (-7.8), which was much higher than that of NAC (-5) but less than the score of the natural agonist N-(3-oxododecanoyl)-l-homoserine (OdDHL) (-8.5). Target 4h (5 mM) decreased the expression of quorum sensing encoding genes in P. aeruginosa PAO1 strain by 53% for pslA, 47% for lasI and lasR, and 29% for filC, lowered PAO1 pyocyanin production by 76.43%, completely blocked the proteolytic activity of PAO1, and did not affect PAO1 cell viability. Targets 4d and 4h may find applications for the prevention and treatment of biofilm-mediated P. aeruginosa local infections of the skin, eye, and wounds. N-(4-Methoxybenzoyl)-l-cysteine 4h is a promising dual-acting matrix disruptive and anti-QS antibiofilm agent for further investigation and optimization.