Pseudomonas aeruginosa adaptation and evolution in patients with cystic fibrosis

Fitness trade-off and the discovery of a novel missense mutation in the PmrB sensor kinase of a colistin-resistant Pseudomonas aeruginosa strain developed by adaptive laboratory evolution

Pseudomonas aeruginosa is a prominent bacterial pathogen that causes several nosocomial infections and is notorious for its environmental resilience and rapid development of resistance to frontline antibiotics. A major cause of mortality and morbidity among cystic fibrosis patients, multidrug-resistant P. aeruginosa is often targeted with the antibiotic colistin as a last option. However, increasing reports of colistin resistance among P. aeruginosa is a significant concern. Though the molecular mechanisms responsible for the development of colistin resistance are well known, the evolutionary trajectory to colistin resistance is an important area of investigation. In this work, using the adaptive laboratory evolution (ALE) approach we have evolved a colistin-sensitive P. aeruginosa ancestral strain to a resistant one. During the process of laboratory evolution in 106 generations, colistin MIC was increased 32-fold. The evolved strain had lower fitness than the ancestral strain, as evidenced by a lower growth rate. Moreover, the evolved strain produced more biofilm and less pyocyanin pigment. Interestingly, the evolved strain showed collateral sensitivity to several antibiotics, including ampicillin, tetracycline, streptomycin, gentamycin, nalidixic acid, trimethoprim, rifampicin, and chloramphenicol. On analysing various TCS modules involved in the development of colistin resistance, a novel missense mutation (V136G) was detected in the PmrB sensor kinase. In silico analysis indicated that the V136G substitution would destabilize the PmrB kinase structure, making the mutation deleterious. However, the functionality of the PmrB mutant remains to be validated experimentally.

Discovery of 3-hydroxypyridin-4(1H)-ones ester of ciprofloxacin as prodrug to combat biofilm-associated Pseudomonas aeruginosa

Chronic infections by Pseudomonas aeruginosa (P. aeruginosa) are frequently complicated due to its ability to form biofilm, which also effectively enhance its resistance to antibiotics. Bacteria-specific antibiotic delivery could locally increase drug concentration to break antimicrobial resistance and reduce the drug's peripheral side effects. The standard-of-care drug ciprofloxacin suffers from severe systemic side effects and was therefore chosen for this approach. It has been identified that 3-hydroxypyridin-4(1H)-one as siderophore mimics could be utilized by P. aeruginosa, and reduced bacterial biofilm formation. In this work, ciprofloxacin was conjugated to 3-hydroxypyridin-4(1H)-one by cleavable linkers to yield prodrugs, which were strategically designed and synthesized to function as dual antibacterial and antibiofilm agents against P. aeruginosa. Conjugate 5c was identified and has the best minimum inhibitory concentrations of 1.07 μM against P. aeruginosa PAO1, and reduced 61.7 % of biofilm formation. In addition, 5c destroyed 75.7 % of mature biofilms. Further studies on the uptake mechanisms showed that the bacterial siderophore-dependent iron transport system was involved in the uptake of the conjugates. Conjugate 5c interfered with iron uptake by bacteria, inhibited their motilities and reduced the production of virulence. Furthermore, prodrug 5c reduced toxicity in vivo and in vitro and showed a positive therapeutic effect in the treatment of Caenorhabditis elegans (C. elegans) infected by P. aeruginosa. These results demonstrate that 3-hydroxypyridin-4(1H)-ones-ciprofloxacin prodrugs are potent in the treatment of biofilm-associated drug-resistant P. aeruginosa infections.

The evolution of carbapenem-resistant Pseudomonas aeruginosa in the COVID-19 era: A global perspective and regional insights

OBJECTIVE

Carbapenem-resistant Pseudomonas aeruginosa (CRPA) is a major contributor to healthcare-associated infections globally. The aim of this study was the impact of the COVID-19 pandemic on the genomic characteristics of P. aeruginosa, particularly clinical CRPA isolates.

METHODS

Clinical data of each patient were collected from the clinical and medical record system. Whole-genome sequencing and bioinformatics analyses were performed to characterize the antibiotic resistance genes (ARGs) and evolutionary dynamics of these isolates. Furthermore, big data analysis was employed to elucidate the genomic characteristics of P. aeruginosa genomes across different periods on a global scale. Statistical analyses were applied to ensure the reliability of the findings.

RESULTS

A total of 628 non-duplicate CRPA isolates were collected, with 256 isolates from before the COVID-19 pandemic and 372 during the pandemic. Only 26.59% of isolates carried carbapenemases, predominantly GES-14, and carbapenemase diversity decreased during the pandemic. However, the diversity of CRPA sequence types (STs) increased, with ST235 and ST244 emerging as the most prevalent clones. The Antibiotic resistance genes (ARGs) number carried by CRPA isolates significantly decreased during the pandemic (P < 0.05), with notable differences in 24 ARGs and 14 virulence factors (VFs) between prepandemic and pandemic periods (χ2 test, P < 0.05). O11 was the predominant serotype across all periods. Global analysis revealed a significant reduction in ARGs in strains from China and Australia (P < 0.01) during the pandemic. Analysis of the global epidemic clones ST244 and ST235 indicated that ARGs in ST244 P. aeruginosa increased significantly during the pandemic.

CONCLUSIONS

Our study highlights the critical need for ongoing surveillance of the evolutionary effects of the COVID-19 pandemic on clinical CRPA isolates, offering an essential theoretical basis for the development of effective and rational control strategies in clinical settings.

Heterogeneity in recombination rates and accessory gene co-occurrence distinguish Pseudomonas aeruginosa phylogroups

Pseudomonas aeruginosa (class Gammaproteobacteria) is a ubiquitous, ecologically widespread, and metabolically versatile species. It is also an opportunistic pathogen that causes a variety of chronic and acute infections in humans. Its ability to thrive in diverse environments and exhibit a wide range of phenotypes lies in part on its large gene pool, but the processes that govern inter-strain genomic variation remain unclear. Here, we aim to characterize the recombination features and accessory genome structure of P. aeruginosa using 840 globally distributed genome sequences. The species can be subdivided into five phylogenetic sequence clusters (corresponding to known phylogroups), two of which are most prominent. Notable epidemic clones are found in the two phylogroups: ST17, ST111, ST146, ST274, and ST395 in phylogroup 1, and ST235 and ST253 in phylogroup 2. The two phylogroups differ in the frequency and characteristics of homologous recombination in their core genomes, including the specific genes that most frequently recombine and the impact of recombination on sequence diversity. Each phylogroup's accessory genome is characterized by a unique gene pool, co-occurrence networks of shared genes, and anti-phage defense systems. Different pools of antimicrobial resistance and virulence genes exist in the two phylogroups and display dissimilar patterns of co-occurrence. Altogether, our results indicate that each phylogroup displays distinct histories and patterns of acquiring exogenous DNA, which may contribute in part to their predominance in the global population. Our study has important implications for understanding the genome dynamics, within-species heterogeneity, and clinically relevant traits of P. aeruginosa.

IMPORTANCE

The consummate opportunist Pseudomonas aeruginosa inhabits many nosocomial and non-clinical environments, posing a major health burden worldwide. Our study reveals phylogroup-specific differences in recombination features and co-occurrence networks of accessory genes within the species. This genomic variation partly explains its remarkable ability to exhibit diverse ecological and phenotypic traits, and thus contribute to circumventing clinical and public health intervention strategies to contain it. Our results may help inform efforts to control and prevent P. aeruginosa diseases, including managing transmission, therapeutic efforts, and pathogen circulation in non-clinical environmental reservoirs.

Hierarchical activation of resistance genes under tetracyclines selective pressure in complex microbial community

The pervasive use of antibiotics exerts selective pressure in both natural and anthropogenic environments, driving the propagation and evolution of antibiotic resistance genes (ARGs) in microbial communities. Understanding the succession of resistome under varying antibiotic stresses is crucial for mitigating the spread of ARGs. This study investigates the succession of resistome under exposure to four structurally different tetracyclines (TC) across concentrations ranging from environmental to clinical levels. A clear hierarchical activation of ARGs was observed, starting with the upregulation of multidrug and TC-specific efflux pump genes, followed by those involved in TC inactivation and ribosomal protection. By identifying the specific thresholds of transcriptional onset times and critical TC concentration ranges that triggered ARG abundance increases, it was found that all ARGs as a whole did not significantly increase when TC concentrations were maintained below 10-5 of the initial minimum inhibitory concentration (MIC0) within 2 h. Similarly, high-risk TC resistance genes do not proliferate when TC concentrations were kept below 10-3 × MIC0 within 24 h. These findings provide quantifiable benchmarks for concentration-time thresholds that can inform the establishment of environmental discharge limits and guide the implementation of targeted treatment technologies to mitigate ARG dissemination.

Monoclonal antibodies derived from B cells in subjects with cystic fibrosis reduce Pseudomonas aeruginosa burden in mice

Pseudomonas aeruginosa (PA) is an opportunistic, frequently multidrug-resistant pathogen that can cause severe infections in hospitalized patients. Antibodies against the PA virulence factor, PcrV, protect from death and disease in a variety of animal models. However, clinical trials of PcrV-binding antibody-based products have thus far failed to demonstrate benefit. Prior candidates were derivations of antibodies identified using protein-immunized animal systems and required extensive engineering to optimize binding and/or reduce immunogenicity. Of note, PA infections are common in people with cystic fibrosis (pwCF), who are generally believed to mount normal adaptive immune responses. Here, we utilized a tetramer reagent to detect and isolate PcrV-specific B cells in pwCF and, via single-cell sorting and paired-chain sequencing, identified the B cell receptor (BCR) variable region sequences that confer PcrV-specificity. We derived multiple high affinity anti-PcrV monoclonal antibodies (mAbs) from PcrV-specific B cells across three donors, including mAbs that exhibit potent anti-PA activity in a murine pneumonia model. This robust strategy for mAb discovery expands what is known about PA-specific B cells in pwCF and yields novel mAbs with potential for future clinical use.

A vasculature-resident innate lymphoid cell population in mouse lungs

Tissue-resident immune cells such as innate lymphoid cells (ILC) are known to reside in the parenchymal compartments of tissues and modulate local immune protection. Here we use intravascular cell labeling, parabiosis and multiplex 3D imaging to identify a population of group 3 ILCs in mice that are present within the intravascular space of lung blood vessels (vILC3). vILC3s are distributed broadly in alveolar capillary beds from which inhaled pathogens enter the lung parenchyma. By contrast, conventional ILC3s in tissue parenchyma are enriched in lymphoid clusters in proximity to large veins. In a mouse model of pneumonia, Pseudomonas aeruginosa infection results in rapid vILC3 expansion and production of chemokines including CCL4. Blocking CCL4 in vivo attenuates neutrophil recruitment to the lung at the early stage of infection, resulting in prolonged inflammation and delayed bacterial clearance. Our findings thus define the intravascular space as a site of ILC residence in mice, and reveal a unique immune cell population that interfaces with tissue alarmins and the circulating immune system for timely host defense.

Loss of OprD function is sufficient for carbapenem-resistance-only but insufficient for multidrug resistance in Pseudomonas aeruginosa

BACKGROUND

Carbapenem-resistant Pseudomonas aeruginosa (CRPA) constitutes a serious source of global healthcare-associated infections, and the exploration of its resistance mechanism represents an important approach to address this issue. Because current research on antibiotic resistance predominantly focuses on multidrug-resistant P. aeruginosa which is widely isolated clinically and the resistance mechanism is complicated. CRPA generally has a higher tolerance to other antibiotics than carbapenem-sensitive P. aeruginosa, yet the specific mechanism of resistance remains poorly understood.

RESULTS

This study delves into the specific antibiotic resistance mechanisms of carbapenem-resistance-only P. aeruginosa (CROPA), a rare kind of pathogen that shows resistance exclusively to carbapenem antibiotics. We collected 11 clinical isolates of CROPA, performed genome sequencing. Our analysis revealed numerous amino acid mutations and premature termination of OprD expression in the CROPA strains. The insertion of IS256 element into OprD in P. aeruginosa was a novel finding. Validation via qPCR and SDS-PAGE affirmed diminished OprD expression levels. Interestingly, common carbapenemases were not detected in our study, and there was no observed upregulation of relevant efflux pumps. The expression of wild-type OprD in CROPA strains restored the sensitivity to carbapenem antibiotics.

CONCLUSIONS

Compared with previous studies on MDR-CRPA, the emergence of CROPA may be directly linked to changes in OprD, while other resistance mechanisms could contribute to broader antibiotic resistance profiles. By focusing on the antibiotic resistance mechanisms of CROPA, this study illuminates the relationship between specific antibiotic resistance mechanisms and antibiotic resistance, providing a theoretical foundation for guiding clinical treatment and developing novel anti-infective agents.

Improved antibacterial activity of a sustained-release biocompatible nanofilm for treating Pseudomonas aeruginosa wound infection in vitro and in vivo

Objectives

The primary goal of this research was to design a useful and biocompatible nanofilm system (CNF) encapsulating chlorhexidine acetate (CHX) for wounds that is endowed with antibacterial and anti-inflammatory activities and promotes wound healing.

Methods

The nanofilm system was developed on the basis of the successful preparation of its nanoemulsion and PVA-CS film system and then important properties of the nanofilm system, including its morphological and physicochemical characteristics, stability and safety, its antimicrobial efficacy against P. aeruginosa was also evaluated in vitro and in vivo. The antibacterial effect, wound healing effect and inflammatory factor change in vivo were evaluated.

Results

These results of this nanofilm system revealed a good particle size (59.27 nm) and stable zeta potential (-15.2 mV) that are suitable for wound healing applications. Additionally, it was stable, exhibited long-term stability (24 months) and sustained release in simulated wound fluid. Results showed that this nanofilm does not induce dose-related toxic effects and displays a better antibacterial effect that occurs more quickly, two times greater than that of CHX in vitro. This safe nanofilm enhances antibacterial activity against P. aeruginosa for 14 days, modulates the immune response, and accelerates skin wound healing in vivo.

Conclusions

These insights into multifunctional nanofilm designs for improved antibacterial effects and sustained release suggest promising clinical applications.

Reduced prevalence of phage defense systems in Pseudomonas aeruginosa strains from cystic fibrosis patients

Cystic fibrosis is a genetic disorder that affects mucus clearance, particularly of the lungs. As a result, cystic fibrosis patients often experience infections from bacteria, which contribute to the disease progression. Pseudomonas aeruginosa is one of the most common opportunistic pathogens associated with cystic fibrosis. The presence of P. aeruginosa complicates the treatment due to its high antibiotic resistance. Thus, research is ongoing to treat these infections with bacterial viruses instead, known as bacteriophages. Notably, P. aeruginosa clinical strains possess a variety of phage defense mechanisms that may limit the effectiveness of phage therapy. In this study, we compared the defense system repertoire of P. aeruginosa strains isolated from cystic fibrosis patients with those from non-cystic fibrosis patients. Our findings reveal that P. aeruginosa strains isolated from cystic fibrosis patients have fewer phage defense mechanisms per strain than from non-cystic fibrosis patients, suggesting altered phage selection pressures in strains colonizing CF patient lungs.IMPORTANCECystic fibrosis patients often experience chronic Pseudomonas aeruginosa lung infections, which are challenging to treat with antibiotics and contribute to disease progression and eventual respiratory failure. Phage therapy is being explored as an alternative treatment strategy for these infections. However, assessing strain susceptibility to phage treatment is essential for ensuring efficacy. To address this, we investigated whether CF-associated clinical P. aeruginosa strains have a distinct phage defense repertoire compared with those isolated from other lung patients. We observed that CF-associated P. aeruginosa strains have significantly fewer phage defenses, possibly affecting the susceptibility of these strains to phage infection.

Unveiling the molecular epidemiology of Pseudomonas aeruginosa in lung infections among cystic fibrosis patients in the Brazilian Amazon

BACKGROUND

Pseudomonas aeruginosa is a major pathogen in cystic fibrosis (CF), where chronic and intermittent infections significantly affect patient outcomes. This study aimed to investigate the molecular epidemiology of P. aeruginosa in CF patients from the Brazilian Amazon, focusing on genotypic diversity, resistance profiles, and virulence factors.

METHODS

A cross-sectional study included 72 P. aeruginosa isolates from 44 CF patients treated at a regional reference center between 2018 and 2019. Antimicrobial susceptibility patterns were determined using VITEK-2 system and Kirby-Bauer disk diffusion. Virulotypes were defined by molecular detection of exoS, exoU, exoT, exoY, algU, and algD genes. Genetic diversity was assessed using multilocus sequence typing (MLST). Demographic data, clinical severity, and spirometry results were also collected.

RESULTS

Among the patients, 54.55% experienced intermittent infections, while 45.45% had chronic infections. Chronic infections were associated with older age, lower FEV1, and reduced Shwachman-Kulczycki scores. Multidrug resistance was observed in 15.3% of isolates, particularly against ciprofloxacin and piperacillin/tazobactam. The exoU gene was present in 55.56% of isolates, an uncommon finding in CF populations. High genetic diversity was evident, with 37 sequence types (STs), including 14 novel STs. High-risk clones (HRCs) constituted 25% of isolates, with ST274 being the most prevalent (12.5%). Longitudinal analysis revealed transient colonization in intermittent infections, while chronic infections were dominated by stable clones.

CONCLUSION

This study highlights the molecular and clinical dynamics of P. aeruginosa in CF patients from the Brazilian Amazon. Chronic infections were linked to severe lung impairment , while intermittent infections were dominated by HRCs. These findings underscore the need for robust genotypic surveillance to mitigate the burden of P. aeruginosa in CF populations.

Inhibitory effects of reumycin produced by Streptomyces sp. TPMA0082 on virulence factors of Pseudomonas aeruginosa

Pseudomonas aeruginosa is an opportunistic human pathogen that causes a wide range of infections. The increasing multidrug-resistance of P. aeruginosa poses a critical challenge for medical care. P. aeruginosa employs virulence factors and biofilms to establish infections in humans and protect itself from environmental stress or antibiotics. These factors are regulated by a quorum sensing mechanism involving multiple regulatory systems that act interdependently through signaling molecules. Therefore, interference with quorum sensing systems can suppress the pathogenicity of P. aeruginosa. In this study, quorum sensing inhibitors were explored from secondary metabolites derived from 111 strains of actinomycetes by targeting the las system, which is thought to be upstream of the quorum sensing cascade in P. aeruginosa. As a result, reumycin was isolated from the culture broth of Streptomyces sp. TPMA0082. Reumycin, a molecule containing a pyrimidotriazine ring, inhibited the binding of the autoinducer to the LasR receptor in the las system, thereby suppressing the production of P. aeruginosa virulence factors, including pyocyanin, rhamnolipids, elastase, motility, and biofilms, without affecting bacterial growth. Toxoflavin, a reumycin derivative with a methyl group at the N1 position, exhibited strong antibacterial activity. Fervenulin, a reumycin derivative with a methyl group at the N8 position, had a negative impact on the logarithmic growth phase of the bacteria and exhibited lower inhibitory activity against virulence factor production compared to reumycin. These findings suggest that the position and number of methyl groups attached to the pyrimidotriazine structure significantly influence its biological activity, exerting distinct effects on quorum sensing inhibition and antibacterial activity.

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 T6SS secretes an oxygen-binding hemerythrin to facilitate competitive growth under microaerobic conditions

Pseudomonas aeruginosa is a prominent respiratory pathogen in cystic fibrosis (CF) patients, thriving in the hypoxic airway mucus. Previous studies have established the role of the oxygen-binding hemerythrin, Mhr, in enhancing P. aeruginosa's fitness under microaerobic conditions. However, the specific mechanisms by which Mhr operates remain unclear. This study uniquely identifies Mhr as an effector of the H2-Type VI Secretion System (H2-T6SS) and elucidates its role in the transport and interaction mechanisms that confer a growth advantage under microaerobic conditions. Our findings demonstrate that mhr expression is directly regulated by Anr and Dnr. Western blot analysis confirms that Mhr is secreted extracellularly via the H2-T6SS. The oxygen-binding Mhr re-enters P. aeruginosa through the OprG porin. Then, Mhr interacts with cbb3-type cytochrome c oxidase (cbb3-CcO) subunits CcoP1/CcoP2, significantly impacting intracellular NADH/NAD+ levels. These insights suggest that the T6SS-mediated secretion and transport of Mhr represent a novel mechanism by which P. aeruginosa acquires and delivers oxygen, potentially enhancing microaerobic respiration, energy production, and growth under microaerobic conditions.

tesG expression as a potential clinical biomarker for chronic Pseudomonas aeruginosa pulmonary biofilm infections

BACKGROUND

Pseudomonas aeruginosa infections in the lungs affect millions of children and adults worldwide. To our knowledge, no clinically validated prognostic biomarkers for chronic pulmonary P. aeruginosa infections exist. Therefore, this study aims to identify potential prognostic markers for chronic P. aeruginosa biofilm lung infections.

METHODS

Here, we screened the expression of 11 P. aeruginosa regulatory genes (tesG, algD, lasR, lasA, lasB, pelB, phzF, rhlA, rsmY, rsmZ, and sagS) to identify associations between clinical status and chronic biofilm infection.

RESULTS

RNA was extracted from 210 sputum samples from patients (n = 70) with chronic P. aeruginosa lung infections (mean age; 29.3-56.2 years; 33 female). Strong biofilm formation was correlated with prolonged hospital stays (212.2 days vs. 44.4 days) and increased mortality (46.2% (18)). Strong biofilm formation is associated with increased tesG expression (P = 0.001), influencing extended intensive care unit (P = 0.002) or hospitalisation stays (P = 0.001), pneumonia risk (P = 0.006), and mortality (P = 0.001). Notably, tesG expression is linked to the modulation of systemic and sputum inflammatory responses and predicts biofilm biomass.

CONCLUSIONS

This study provides the first clinical dataset of tesG expression levels as a predictive biomarker for chronic P. aeruginosa pulmonary infections.

Whole proteome-integrated and vaccinomics-based next generation mRNA vaccine design against Pseudomonas aeruginosa-A hierarchical subtractive proteomics approach

Pseudomonas aeruginosa (P. aeruginosa) is a multidrug-resistant opportunistic pathogen responsible for chronic obstructive pulmonary disease (COPD), cystic fibrosis, and ventilator-associated pneumonia (VAP), leading to cancer. Developing an efficacious vaccine remains the most promising strategy for combating P. aeruginosa infections. In this study, we employed an advanced in silico strategy to design a highly efficient and stable mRNA vaccine using immunoinformatics tools. Whole proteome data were utilized to identify highly immunogenic vaccine candidates using subtractive proteomics. Three extracellular proteins were prioritized for T- and linear B-cell epitope prediction. Beta-definsin protein sequence was incorporated as an adjuvant at the N-terminus of the construct. A total of 3 CTL, 3 HTL, and 3 linear B cell highly immunogenic epitopes were combined using specific linkers to design this multi-peptide construct. The 5' and 3' UTR sequences, Kozak sequence with a stop codon, and signal peptides followed by a poly-A tail were incorporated into the above vaccine construct to create our final mRNA vaccine. The vaccines exhibited antigenicity scores >0.88, ensuring high antigenicity with no allergenic or toxic. Physiochemical properties analysis revealed high solubility and thermostability. Three-dimensional structural analysis determined high-quality structures. Vaccine-receptor docking and molecular dynamic simulations demonstrated strong molecular interactions, stable binding affinities, dynamic nature, and structural stability of this vaccine, with significant immunogenic responses of the immune system against the vaccine. The immunological simulation indicates successful cellular and humoral immune responses to defend against P. aeruginosa infection. Validation of the study outcomes necessitates both experimental and clinical testing.

Luteolin: A novel approach to fight bacterial infection

Diseases caused by bacteria significantly impact public health, causing both acute and chronic issues, sequelae, and death. The problems get even more significant, considering the antimicrobial resistance. Bacterial resistance occurs when antibacterial drugs fail to kill the microbes, leading to the persistence of infection and pathogen spread in the host. Thus, the search for new molecules with antibacterial activity dramatically impacts human health. Natural products have proven to be a prosperous source of these agents. Among them, the flavonoids deserve to be highlighted. They are secondary metabolites, primarily involved in plant signaling and protection. Thus, they play an essential role in plant adaptation to the environment. Herein, we will focus on luteolin because it is commonly found in edible plants and has diverse pharmacological properties such as anti-inflammatory, anticancer, antioxidant, and antimicrobial. We will further explore the luteolin antibacterial activity, mechanisms of action, structure-activity relationship, and toxicity of luteolin. Thus, we have included reports of luteolin with antibacterial activity recently published, as well as focused on nanotechnology as a pivotal and helpful approach for the clinical use of luteolin. This review aims to foster future research on luteolin as a therapeutic agent for treating bacterial infection.

Exploring Marine natural products as potential Quorum sensing inhibitors by targeting the PqsR in Pseudomonas aeruginosa: Virtual screening assisted structural dynamics study

Antibiotic resistance is a critical global health issue, and Pseudomonas aeruginosa is a particularly challenging pathogen. This gram-negative bacterium is notorious for its high virulence and resistance to antimicrobial agents, making it a leading cause of nosocomial infections, significantly impacting public health. The adaptability and multidrug resistance of P. aeruginosa exacerbate treatment difficulties, resulting in increased morbidity and mortality rates worldwide. Consequently, targeting bacterial quorum sensing (QS) systems is a promising strategy for the development of novel antimicrobial compounds against this resilient pathogen. In this study, a structure-based virtual screening (SBVS) approach was employed to identify marine natural products (MNPs) as potential lead molecules targeting the biofilm-forming PqsR protein of P. aeruginosa. A total of ~37,000 MNPs were initially evaluated and ranked based on docking scores using high-throughput virtual screening (HTVS), Standard Precision (SP), and Extra Precision (XP) methods. Ten lead molecules (five from the CMNPD database and five from the MNPD database) were shortlisted based on their docking scores (<-10.0 kcal/mol) and binding free energy values (MM-GBSA ΔG <-40 kcal/mol). Their drug-likeness profiles were assessed using stringent criteria in the QikProp module of Schrödinger, and their chemical reactivity was evaluated through density functional theory (DFT) calculations. The structural and energetic interactions between the identified MNPs and the PqsR-binding pocket were validated through molecular dynamics simulations (MDS) and binding free energy (BFE) calculations. Structural dynamic analyses revealed that the MNP-bound PqsR complexes demonstrated stable interactions within the binding pocket, with hydrophobic residues such as L208, I236, and I263 playing a crucial role in maintaining stability. Among the identified MNPs, CMNPD14329, CMNPD23880, MNPD13399, and MNPD13725 emerged as promising lead molecules for further research. These candidates can serve as foundations for developing structural analogs with enhanced binding affinities for PqsR and other biofilm-forming proteins. Further experimental validation is essential to confirm the therapeutic potential of these identified MNPs.

Bacterial cell wall-specific nanomedicine for the elimination of Staphylococcus aureus and Pseudomonas aeruginosa through electron-mechanical intervention

Personalized synergistic antibacterial agents against diverse bacterial strains are receiving increasing attention in combating antimicrobial resistance. However, the current research has been struggling to strike a balance between strain specificity and broad-spectrum bactericidal activity. Here, we propose a bacterial cell wall-specific antibacterial strategy based on an in situ engineered nanocomposite consisting of carbon substrate and decorated TiOx dots, termed TiOx@C. The fiber-like carbon substrate of TiOx@C is able to penetrate the bacterial membrane of Pseudomonas aeruginosa (P. aeruginosa), but not that of Staphylococcus aureus (S. aureus) due to its thicker bacterial wall, thus achieving bacterial wall specificity. Furthermore, a series of experiments demonstrate the specific electro-mechanical co-sterilization effect of TiOx@C. On the one hand, TiOx@C can disrupt the electron transport chain and block the energy supply of S. aureus. On the other hand, TiOx@C capable of destroying the membrane structure of P. aeruginosa could cause severe mechanical damage to P. aeruginosa as well as inducing oxidative stress and protein leakage. In vivo experiments demonstrate the efficacy of TiOx@C in eliminating 97% of bacteria in wounds and promoting wound healing in wound-infected female mice. Overall, such a bacterial cell wall-specific nanomedicine presents a promising strategy for non-antibiotic treatments for bacterial diseases.

Harnessing the human gut microbiota: an emerging frontier in combatting multidrug-resistant bacteria

Antimicrobial resistance (AMR) has become a major and escalating global health threat, undermining the effectiveness of current antibiotic and antimicrobial therapies. The rise of multidrug-resistant bacteria has led to increasingly difficult-to-treat infections, resulting in higher morbidity, mortality, and healthcare costs. Tackling this crisis requires the development of novel antimicrobial agents, optimization of current therapeutic strategies, and global initiatives in infection surveillance and control. Recent studies highlight the crucial role of the human gut microbiota in defending against AMR pathogens. A balanced microbiota protects the body through mechanisms such as colonization resistance, positioning it as a key ally in the fight against AMR. In contrast, gut dysbiosis disrupts this defense, thereby facilitating the persistence, colonization, and dissemination of resistant pathogens. This review will explore how gut microbiota influence drug-resistant bacterial infections, its involvement in various types of AMR-related infections, and the potential for novel microbiota-targeted therapies, such as fecal microbiota transplantation, prebiotics, probiotics, phage therapy. Elucidating the interactions between gut microbiota and AMR pathogens will provide critical insights for developing novel therapeutic strategies to prevent and treat AMR infections. While previous reviews have focused on the general impact of the microbiota on human health, this review will specifically look at the latest research on the interactions between the gut microbiota and the evolution and spread of AMR, highlighting potential therapeutic strategies.

Low leucine levels in the blood enhance the pathogenicity of neonatal meningitis-causing Escherichia coli

Neonatal bacterial meningitis is associated with substantial mortality and morbidity worldwide. Neonatal meningitis-causing Escherichia coli (NMEC) is the most common gram-negative bacteria responsible for this disease. However, the interactions of NMEC with its environment within the host are poorly understood. Here, we showed that a low level of leucine, a niche-specific signal in the blood, promotes NMEC pathogenicity by enhancing bacterial survival and replication in the blood. A low leucine level downregulates the expression of NsrP, a small RNA (sRNA) identified in this study, in NMEC in an Lrp-dependent manner. NsrP destabilizes the mRNA of the purine biosynthesis-related gene purD by direct base pairing. Decreased NsrP expression in response to low leucine levels in the blood, which is a purine-limiting environment, activates the bacterial de novo purine biosynthesis pathway, thereby enhancing bacterial pathogenicity in the host. Deletion of NsrP or purD significantly increases or decreases the development of E. coli bacteremia and meningitis in animal models, respectively. Furthermore, we showed that intravenous administration of leucine effectively reduces the development of bacteremia and meningitis caused by NMEC by blocking the Lrp-NsrP-PurD signal transduction pathway. This study provides a potential strategy for the prevention and treatment of E. coli-induced meningitis.

Spatial transcriptomics identifies novel Pseudomonas aeruginosa virulence factors

To examine host-pathogen interactions, we leveraged a dual spatial transcriptomics approach that simultaneously captures the expression of Pseudomonas aeruginosa genes alongside the entire host transcriptome using a murine model of ocular infection. This method revealed differential pathogen- and host-specific gene expression patterns in infected corneas, which generated a unified transcriptional map of infection. By integrating these data, we developed a predictive ridge regression model trained on images from infected tissues. The model achieved an R2 score of 0.923 in predicting bacterial burden distributions and identifying novel biomarkers associated with disease severity. Among iron acquisition pathogen-specific gene transcripts that showed significant enrichment at the host-pathogen interface, we discovered the novel virulence mediator PA2590, which was required for bacterial virulence. This study therefore highlights the power of combining bacterial and host spatial transcriptomics to uncover complex host-pathogen interactions and identify potentially druggable targets.

High prevalence of carbapenem-resistant Pseudomonas aeruginosa and identification of a novel VIM-type metallo-β-lactamase, VIM-92, in clinical isolates from northern China

Carbapenem-resistant Pseudomonas aeruginosa (CRPA) has become a serious global health concern due to the limited treatment options. The primary resistance mechanism in CRPA involves the production of metallo-β-lactamases (MBLs), making MBL-producing P. aeruginosa a significant component of CRPA cases. To understand the prevalence of CRPA in hospitals in northern China, we conducted a preliminary screening and identification of CRPA in 143 clinical isolates of P. aeruginosa collected from various departments of a tertiary hospital between 2021 and 2023, analyzing CRPA resistance trends in certain regions of northern China during this period. We identified 71 CRPA isolates that exhibited high carbapenem resistance and phylogenetic tree analysis revealed that ST244 CRPA isolates had widely spread across various departments of the same hospital over three consecutive years. We also identified two VIM-producing isolates, PJK40 and PJK43, both of which carried the same novel VIM-type metallo-β-lactamase, VIM-92, encoded by a newly identified gene, bla VIM-92, closely related to bla VIM-24. bla VIM-92 was embedded in class 1 integrons within the Tn1403 transposon. The bla VIM-92-carrying plasmid, pPJK40, was found to resemble the pJB37 megaplasmid. The expression of VIM-92 and VIM-24 in DH5α and PAO1 revealed similar effects of the MICs of β-lactams, except for aztreonam. The high prevalence of CRPA in clinical settings, and the identification of VIM-92, highlights the urgent need for ongoing surveillance of CRPA and emerging MBL variants in P. aeruginosa.

A VgrG2b fragment cleaved by caspase-11/4 promotes Pseudomonas aeruginosa infection through suppressing the NLRP3 inflammasome

The T6SS of Pseudomonas aeruginosa plays an essential role in the establishment of chronic infections. Inflammasome-mediated inflammatory cytokines are crucial for host defense against bacterial infections. We found that P. aeruginosa infection activates the non-canonical inflammasome in macrophages, yet it inhibits the downstream activation of the NLRP3 inflammasome. The VgrG2b of P. aeruginosa is recognized and cleaved by caspase-11, generating a free C-terminal fragment. The VgrG2b C-terminus can bind to NLRP3, inhibiting the activation of the NLRP3 inflammasome by rejecting NEK7 binding to NLRP3. Administration of a specific peptide that inhibits caspase-11 cleavage of VgrG2b significantly improves mouse survival during infection. Our discovery elucidates a mechanism by which P. aeruginosa inhibits host immune response, providing a new approach for the future clinical treatment of P. aeruginosa infections.

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.

Risk Factors for Development and Mortality of Carbapenem-Resistant Pseudomonas aeruginosa Bloodstream Infection in a Chinese Teaching Hospital: A Seven-Year Retrospective Study

Objective

Pseudomonas aeruginosa (P. aeruginosa) is a gram-negative opportunistic pathogen, which can cause acute and chronic infections, often resulting in high mortality. The aim of this study was to investigate the risk factors for the development and mortality of patients with carbapenem-resistant P. aeruginosa bloodstream infection (CRPA BSI).

Methods

A total of 112 patients with CRPA BSI and 112 patients with carbapenem-sensitive P. aeruginosa (CSPA) BSI were included from a Chinese teaching hospital from January 2017 to December 2023 in this retrospective cohort study. The detection rate, antimicrobial susceptibility of P. aeruginosa and clinical characteristics of these patients were investigated. Multivariable logistic regression analysis was used to identify risk factors for the development and outcomes of CRPA BSI.

Results

In the past 7 years, 7480 blood samples of P. aeruginosa were cultured in the hospital. The detection rates of CRPA, multidrug resistant P. aeruginosa (MDRPA), and difficult-to-treat resistant P. aeruginosa (DTRPA) BSI increased annually (26% to 47%, 10% to 36% and 5% to 15%, respectively). CRPA showed high resistance to conventional antibiotics. Chronic lung disease (OR 3.953, 95% CI 1.131-13.812), transplantation (OR 2.837, 95% CI 1.036-7.770), multi-organ failure (OR 4.815, 95% CI 1.949-11.894), pre-infection within CRPA (OR 9.239, 95% CI 3.441-24.803), and exposure to carbapenems within 90 days (OR 2.734, 95% CI 1.052 -7.106) were independent risk factors for the development of CRPA bacteremia. Sepsis or septic shock (OR 8.774, 95% CI 3.140-24.515, p = 0.001) were independent risk factors of mortality.

Conclusion

Chronic lung disease, transplantation, multi-organ failure, prior CRPA infection, and prior carbapenems exposure are independent risk factors for the development of CRPA bacteremia. Sepsis or septic shock increases 28-day mortality. To investigate the molecular mechanisms of carbapenem-resistance of P. aeruginosa, standardize antibiotic usage, and assess risk factors for the development and mortality of CRPA BSI are beneficial to control infection and reduce death.

Circulating microbiome DNA features and its effect on predicting clinicopathological characteristics of patients with colorectal cancer

BACKGROUND

Colorectal cancer (CRC) presents a complex tumor microenvironment influenced by genetic and microbial factors. Microbial DNA from the gut and tumor microenvironment can translocate into the bloodstream, forming a circulating microbiome associated with prognosis and clinicopathological features. This study investigates the peripheral venous blood microbiome in CRC patients using 2bRAD-M sequencing and evaluates its clinical significance.

METHODS

Peripheral venous blood samples from 29 CRC patients (19 males, 10 females; mean age 57 years) and 10 healthy controls were analyzed to assess microbial diversity. Additionally, 20 tumor tissue samples from CRC patients were examined via RT-qPCR to validate blood-tumor microbial correlations. Statistical analyses evaluated associations between microbial abundance and clinical features, including metastasis and PD-L1 Combined Positive Score (CPS). Comparative analyses between CRC patients and healthy controls were performed to identify disease-specific microbial signatures.

RESULTS

A total of 270 microbial species were identified, with dominant phyla including Actinomycetota, Bacillota, Bacteroidota, and Pseudomonadota. Bosea lupini was significantly associated with metastasis stage (p = 0.034), while Mycobacterium tuberculosis (p = 0.022), Porphyromonas pasteri (p = 0.017), and Bosea lupini (p = 0.045) correlated with CPS. Microbes such as Bosea lupini, Ralstonia mannitolilytica, and Porphyromonas pasteri suggested potential tumor-derived translocation into the bloodstream.

CONCLUSION

This study identifies a distinct peripheral venous blood microbiome in CRC patients, highlighting specific microbes associated with clinicopathological features and disease progression. These findings suggest the potential of blood microbiomes as noninvasive biomarkers for CRC prognosis and therapeutic targets, warranting further investigation in larger cohorts.

Regulation of the H1 Type VI Secretion System by the Transcriptional Regulator NfxB in Pseudomonas aeruginosa

The type VI secretion system (T6SS) is a widely distributed molecular apparatus found in most Gram-negative bacteria. Studies show that T6SSs have functions in bacterial virulence, inter- and intra-bacterial competition, and environmental adaptation. Pseudomonas aeruginosa, an opportunistic pathogen, harbors three T6SS gene clusters that perform diverse roles in clinical infection. Herein, using DNA affinity chromatography of the H1-T6SS promoter, the fluoroquinolone antibiotic resistance regulator NfxB was identified. Further studies demonstrated that NfxB negatively regulates the expression of H1-T6SS by directly binding to its promoter region. T6SS expression and effector secretion are regulated by the fluoroquinolone antibiotic via NfxB, which enhances inter-bacterial competition in the complex bacterial ecology. Meanwhile, the deletion of nfxB alters carbenicillin resistance through an unknown pathway. This study provides new insights into the regulation of T6SS by environmental signals, and it provides data support for antibiotic resistance and inter-bacterial competition due to T6SSs.

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.

Quantitative LC-MS/MS Analysis of Endogenous Pseudomonas aeruginosa Isomeric Metabolites Biliverdin IX Alpha, Beta, and Delta in Cell Culture Supernatant, Cell Pellet, and Lung Tissue

Pseudomonas aeruginosa (Pa) utilizes heme as an iron source from the host during infection. Biliverdin beta and delta (BVIXβ and BVIXδ) are generated by HemO, specific to Pa, while biliverdin alpha is generated from the bacterial BphO system and by mammalian heme oxygenases. Here, we have developed and characterized a quantitative LC-MS/MS assay for the separation of three endogenous isomers, BVIXα, BVIXβ, and BVIXδ. The assay was validated for accuracy, precision, linearity, extraction recovery, solution stability, freeze-thaw stability, benchtop stability, postextraction stability, and nonspecific oxidation of BVIX. The addition of an antioxidant, butylated hydroxytoluene, during sample preparation is needed in order to prevent coupled oxidation from inflating quantitative values of BVIX. The assay development included optimization of a liquid-liquid extraction for bacterial culture supernatants and sample preparation procedures for cell pellets and tissue homogenate to reduce sample demand and automate the extraction procedure in a 96-well format, to enhance extraction throughput. This method was applied to analyze isomer distribution in Pa supernatant, bacterial pellet, and infected lung tissue from Pa-challenged mice. This method can be used in the future for low-volume culture samples, as well as tissue samples, to understand the mechanisms of virulence and inform future drug development.

Exploring the antibacterial and anti-biofilm activity of two Iranian medical-grade kinds of honey on multidrug-resistant Pseudomonas aeruginosa

INTRODUCTION

Pseudomonas aeruginosa is a prominent multidrug-resistant and biofilm-forming bacteria. Mono-floral honey, enriched with a variety of biological compounds, can be categorized as medical-grade honey due to its notable pharmacological benefits. In this study, two types of Iranian honey were thoroughly characterized, and the antimicrobial and anti-biofilm properties were examined against three clinical strains of multidrug-resistant P. aeruginosa.

METHODS

Citrus and Thyme honey from Alborz were selected based on physicochemical, phytochemical, and melissopalynological tests conducted from a medical perspective. The antibacterial activity of the honey samples against three clinical strains of multidrug-resistant P. aeruginosa isolated from wound infections was evaluated using both the well-diffusion and broth microdilution methods. Additionally, an antibiofilm assay was performed using the crystal violet method in microplates.

RESULTS

Both medical grade honey samples exhibited considerable antibacterial activity against the three P. aeruginosa isolates at 75-100% v/v concentrations with inhibition zones measuring between 15 and 30 mm. The minimum inhibitory concentration (MIC) and the minimum bactericidal concentration (MBC) values for both types of honey were 6.25% v/v (final concentration). The antibiofilm assay indicated that both types of honey demonstrated varying levels of antibiofilm activity. Citrus honey at 9% concentration was the most effective, showing an average inhibition rate of 59%, while Citrus honey at 2.3% final concentration exhibited the least effectiveness with an average inhibition rate of 23%.

DISCUSSION

A thorough analysis of the honeys studied confirmed their authenticity and the presence of medicinal compounds. The results of honey tests correspond to the normal range (natural Honey) in the Council of the European Union. Based on the evaluation and compliance with the medical grade criteria including authenticity, health, qualities well botanical origin mentioned honey is classified in medical grade. The antibacterial results indicated that both Thyme and Citrus honeys effectively inhibit the growth and biofilm formation of P. aeruginosa. Therefore, these honeys may serve as natural and safe alternatives or adjuncts to conventional antibiotic therapy for wound healing and infection management.

Molecular Markers Specific for the Pseudomonadaceae Genera Provide Novel and Reliable Means for the Identification of Other Pseudomonas Strains/spp. Related to These Genera

Background/Objectives: Taxon-specific conserved signature indels (CSIs) exhibit a strong predictive ability of being found in other members of specific taxa/genera. Recently, multiple exclusively shared CSIs were identified for several newly described Pseudomonadaceae genera (viz. Aquipseudomonas, Atopomonas, Caenipseudomonas, Chryseomonas Ectopseudomonas, Geopseudomonas, Halopseudomonas, Metapseudomonas, Phytopseudomonas, Serpens, Stutzerimonas, Thiopseudomonas, and Zestomonas). This study examines the potential applications of these CSIs for identifying other Pseudomonas spp. (strains) related to these genera. Methods: This work utilized the AppIndels.com server, which uses information regarding the presence of known taxon-specific CSIs in a genome for predicting its taxonomic affiliation. For this purpose, sequence information for different CSIs specific for the Pseudomonadaceae species/genera were added to the server's database. Results: The AppIndels server was used to predict the taxonomic affiliation of 1972 genomes of unclassified Pseudomonas spp. (strains/isolates). Based upon finding a significant number of CSIs matching a specific taxon, the AppIndels server made positive predictions regarding the taxonomic affiliation of 299 examined genomes into the following clades/genera: Pseudomonas sensu stricto clade (46), Pseudomonas aeruginosa (64), Ectopseudomonas (46), Chryseomonas (32), Stutzerimonas (31), Metapseudomonas (22), Aquipseudomonas (21), Phytopseudomonas (17), Halopseudomonas (9), Geopseudomonas (4), Thiopseudomonas (3), Serpens (2), and Caenipseudomonas and Zestomonas (1 each). Phylogenetic studies confirmed that the taxonomic predictions by the server were 100% accurate. Conclusions: Our results demonstrate that the CSIs specific for Pseudomonadaceae species/genera, in conjunction with the AppIndels server, provides a novel and useful tool for identifying other species/strains affiliated with these species/genera. Phylogenetic studies suggest that many examined Pseudomonas strains constitute novel species in the indicated genera.

Outer membrane vesicle contributes to the Pseudomonas aeruginosa resistance to antimicrobial peptides in the acidic airway of bronchiectasis patients

Pseudomonas aeruginosa is the predominant pathogen causing chronic infection in the airway of patients with bronchiectasis (BE), a chronic respiratory disease with high prevalence worldwide. Environmental factors are vital for bacterial successful colonization. Here, with sputa and bronchoalveolar lavage fluids, we determined that the concentration of airway antimicrobial peptide LL-37 and lactate was elevated in BE patients, especially in those infected with P. aeruginosa. The in vitro antibacterial assay revealed the bactericidal activity of LL-37 against the clinical P. aeruginosa isolates, which were dampened in the acidic condition. P. aeruginosa production of outer membrane vesicles (OMVs) enhanced in the lactate-adjusted acidic condition. Transcriptomic analysis suggested that OMVs induce the hyperproduction of the chemical compound 2-heptyl-4-quinolone (HHQ) in the bacterial population, which was verified by high-performance liquid chromatography. The positively charged HHQ interfered with the binding of LL-37 to bacterial cell membrane, potentiating the P. aeruginosa resistance to LL-37. To our knowledge, this is a new resistance mechanism of P. aeruginosa against antimicrobial peptides and may provide theoretical support for the development of new antibacterial therapies.

Clinical aspects and characterization of Pseudomonas aeruginosa isolated from patients infected with SARS-CoV-2

AIMS

This study aimed to identify and characterize Pseudomonas aeruginosa isolates from patients infected and uninfected with SARS-CoV-2, focusing on their phenotypic characteristics and antimicrobial resistance profiles.

MAIN METHODS

A total of 100 P. aeruginosa isolates were obtained from patients admitted to a hospital in Presidente Prudente, SP, in 2021. The isolates were assessed for antimicrobial resistance, pyocyanin, lipase and phospholipase C production, biofilm formation, and the presence of virulence factor genes, including those associated with metallo-β-lactamase (MBL) production.

KEY FINDINGS

Among the isolates, 58 were from patients infected with SARS-CoV-2 and 42 from non-infected patients. P. aeruginosa was predominantly isolated from tracheal secretion samples in infected patients, while urine samples were more common in non-infected patients. Notably, patients with SARS-CoV-2 exhibited a higher rate of resistance to aztreonam and used a wider range of antibiotics. Isolates from infected patients demonstrated higher phospholipase C production and a greater number classified as strong biofilm formers. Virulence factor genes were present in at least 70 % of the isolates, while only three isolates showed genes for MBL production.

SIGNIFICANCE

The findings of this study indicate that the COVID-19 pandemic creates a favorable environment for the increase of secondary infections by P. aeruginosa. Understanding the characteristics and resistance profiles of these isolates is crucial for improving treatment strategies and patient outcomes.

Citrus maxima extract-coated versatile gold nanoparticles display ROS-mediated inhibition of MDR-Pseudomonas aeruginosa and cancer cells

The expanding prevalence of microbial resistance to conventional treatments has triggered a race to develop alternative/improved strategies to combat drug-resistant microorganisms in an efficient manner. Here, the lethal impact of the biosynthesized gold nanoparticles (AuNPs) against multi-drug resistant (MDR) bacteria has been elucidated. AuNPs, synthesized from the extracts of the fruit, leaf and peel of the Citrus maxima plant, were physicochemically characterized by UV-Vis spectrophotometry, Dynamic Light Scattering (DLS), electron microscopy and spectroscopic techniques not only confirmed the production of AuNPs of size below 100 nm but also identified the phytochemicals adsorbed onto the surface of NPs. AuFeNP not only showed excellent antioxidant activity (∼95 % at 1 mg/mL) but also exhibited a commendable antimicrobial activity against MDR-Pseudomonas aeruginosa as assessed by the zone of inhibition (13.5 mm) and microwell broth dilution assays (9.5 μg/mL, MIC). Transmission electron microscopy (TEM) displayed bacterial cell membrane destruction post-AuNPs exposure. The killing mechanism of AuNPs elucidated the permeabilization of the cell membrane and generation of reactive oxygen species (ROS), ∼10-fold high depletion of GSH, and eventually leaching protein out of the cell. DNA damage, as a marker of apoptosis, was also noticed, which could be an implication of ROS accumulation in MDR-PA. AuNPs displayed significant toxicity at ∼ 10 μg/mL on various cancer cells (HT-1080, MRC-5, MDA-MB-231 and B16-F10) and relatively low toxicity on normal cells (MRC-5 and HaCaT). Scratch assay to identify the migration capability of breast cancer cells on treatment with AuNPs deciphered hampering of migration potential of breast cancer cells. Apoptotic topographies in B16-F10 cells were confirmed using AO/EtBr dual dye staining, DNA fragmentation, Caspase-3 assay and cell cycle analysis using flow cytometry. Hemolysis revealed minimal toxicity of AuNPs on human red blood cells. Nominal toxicity (∼70 % survival at 500 μg/mL of AuNPs) on mammalian cells was evaluated using Cell Titer-Glo cell viability assay. Overall results advocate the promising potential of biosynthetic AuFeNP against multi-drug-resistant pathogens and for further formulation into anticancer agents.

Within-host evolution of a transcriptional regulator contributes to the establishment of chronic Pseudomonas aeruginosa infection

As an opportunistic pathogen, Pseudomonas aeruginosa can cause both acute and chronic infections that are notoriously difficult to treat. However, the mechanism underlying acute or chronic P. aeruginosa infection remains unclear. Here, we identify a mutation in a transcriptional regulator PA5438 (named GavR). This mutation causes a 3-amino-acid absence in GavR and is strongly associated with chronic P. aeruginosa infection. Mechanistically, the deletion in GavR directly downregulates the transcription of the aceEF operon and leads to an accumulation of intracellular pyruvate, which can promote bacterial survival in neutrophils. Notably, P. aeruginosa with 9-bp-deleted or full-length gavR composes a mixed population in most patients with chronic or acute infections. Overall, the mutation in gavR attenuates P. aeruginosa virulence and enhances innate immune evasion by reprogramming pyruvate metabolism and the glyoxylate cycle. This work reveals a molecular mechanism of transition control from acute to chronic infection in P. aeruginosa.

Insights into the diverse roles of the terminal oxidases in Burkholderia cenocepacia H111

Burkholderia cenocepacia H111 is an obligate aerobic bacterium which has been isolated from a cystic fibrosis (CF) patient. In CF lungs the environment is considered micro-oxic or even oxygen-depleted due to bacterial activities and limited oxygen diffusion in the mucus layer. To adapt to low oxygen concentrations, bacteria possess multiple terminal oxidases. In this study, we identified six terminal oxidases of B. cenocepacia H111 and constructed reporter strains to monitor their expression in different environments. While the heme-copper oxidase aa3 (cta) was constitutively expressed, the bd-1 oxidase (cyd) was induced under oxygen-limited growth conditions. The cyanide-insensitive bd-type terminal oxidase (cio-1) was mainly expressed in cells grown on the surface of solid medium or in liquid cultures in presence of cyanide, which is known to be produced in the CF lung by the often co-residing CF pathogen Pseudomonas aeruginosa. Indeed, a cio-1 insertional mutant was not able to grow in the presence of cyanide confirming the important role of Cio-1 in cyanide resistance. The caa3 oxidase (caa), was only expressed under nutrient limitation when cells were grown on the surface of solid medium. We also investigated the involvement of two regulatory systems, Anr and RoxS/RoxR, in the expression of cio-1 and cyd. Our data suggest, that, given that Cio-1 is only present in prokaryotes and plays an important role in the defense against cyanide-producing P. aeruginosa, it may be a valuable drug target for treatment of polymicrobial infections in CF patients.

Dual RNA sequencing of a co-culture model of Pseudomonas aeruginosa and human 2D upper airway organoids

Pseudomonas aeruginosa is a Gram-negative bacterium that is notorious for airway infections in cystic fibrosis (CF) subjects. Bacterial quorum sensing (QS) coordinates virulence factor expression and biofilm formation at population level. Better understanding of QS in the bacterium-host interaction is required. Here, we set up a new P. aeruginosa infection model, using 2D upper airway nasal organoids that were derived from 3D organoids. Using dual RNA-sequencing, we dissected the interaction between organoid epithelial cells and WT or QS-mutant P. aeruginosa strains. Since only a single healthy individual and a single CF subject were used as donors for the organoids, conclusions about CF-specific effects could not be deduced. However, P. aeruginosa induced epithelial inflammation, whereas QS signaling did not affect the epithelial airway cells. Conversely, the epithelium influenced infection-related processes of P. aeruginosa, including QS-mediated regulation. Comparison of our model with samples from the airways of CF subjects indicated that our model recapitulates important aspects of infection in vivo. Hence, the 2D airway organoid infection model is relevant and may help to reduce the future burden of P. aeruginosa infections in CF.

Modification of Ti13Nb13Zr Alloy Surface via Plasma Electrolytic Oxidation and Silver Nanoparticles Decorating

The dynamically developing field of implantology requires researchers to search for new materials and solutions. In this study, TiNbZr samples were investigated as an alternative for popular, but potentially hazardous TiAl6V4. Samples were etched, sandblasted, subjected to PEO, and covered in AgNP suspension. Simultaneously, SEM images were taken, and the wettability and roughness of the surface were measured. Samples covered in AgNPs were subjected to biological trials. A six-day measurement of human fibroblast proliferation was conducted to assess biocompatibility, and the population of E. coli and S. aureus was measured over eight hours. Results showed that the TiNbZr PEO surface is biocompatible with human fibroblast cells and promotes growth. However, deposited AgNPs exhibited only slight effectiveness in decreasing bacterial growth over the first two hours. The results suggest that the method of surface preparation is sufficient and might promote osseointegration. On the other hand, more efficient and reliable methods of application of AgNPs should be researched.

Nutrient conditions affect antimicrobial pharmacodynamics in Pseudomonas aeruginosa

The infectious microenvironment in chronic respiratory tract infections is characterized by substantial variability in nutrient conditions, which may impact colonization and treatment response of pathogens. Metabolic adaptation of the cystic fibrosis (CF)-associated pathogen Pseudomonas aeruginosa has been shown to lead to changes in antibiotic sensitivity. The impact of specific nutrients on the response to antibiotics is, however, poorly characterized. Here, we investigated how different carbon sources impact the antimicrobial pharmacodynamic responses in P. aeruginosa. We evaluated the effect of six antibiotics (aztreonam, ceftazidime, ciprofloxacin, colistin, imipenem, and tobramycin) on P. aeruginosa cultured in a basal medium enriched for seven different carbon sources (alanine, arginine, aspartate, glucose, glutamate, lactate, and proline). Pharmacodynamic responses were characterized by measuring time-kill profiles for a bioluminescent P. aeruginosa PAO1 Xen41 strain. We show that single-nutrient modifications minimally affected bacterial growth rate. For specific nutrient-antibiotic combinations, we find relevant alterations in antibiotic sensitivity (i.e., EC50) and the maximum drug effect (Emax), in particular for ciprofloxacin, colistin, imipenem, and tobramycin. The most pronounced effect was observed for tobramycin, where glucose was found to reduce the EC50 (0.5-fold), whereas lactate-enriched conditions led to a 4.3-fold increase in EC50. Using pharmacokinetic-pharmacodynamic simulations, we illustrate that the magnitude of the nutrient-driven pharmacodynamic changes impact treatment for clinical dosing strategies of tobramycin. In summary, this study underscores the impact of nutrient composition on antimicrobial pharmacodynamics, which could potentially contribute to observed variability of antimicrobial treatment responses in CF patients.IMPORTANCEChronic respiratory tract infections in cystic fibrosis patients present significant challenges for antibiotic treatment due to the complexity of the respiratory environment. This study investigated how variations in nutrient levels, altered during chronic infections, affect pathogen response to antibiotics in an experimental setting. By simulating different nutrient conditions, we aimed to uncover interactions between nutrient availability and antibiotic sensitivity. Our findings provide critical insights that could lead to more effective treatment strategies for managing chronic respiratory tract infections in cystic fibrosis patients while also guiding future research in improving treatment methodologies.

Whole-Genome Sequencing of Resistance, Virulence and Regulation Genes in Extremely Resistant Strains of Pseudomonas aeruginosa

BACKGROUND/OBJECTIVES

Pseudomonas aeruginosa is a clinically significant opportunistic pathogen, renowned for its ability to acquire and develop diverse mechanisms of antibiotic resistance. This study examines the resistance, virulence, and regulatory mechanisms in extensively drug-resistant clinical strains of P. aeruginosa.

METHODS

Antibiotic susceptibility was assessed using the Minimum Inhibitory Concentration (MIC) method, and whole-genome sequencing (WGS) was performed on the Illumina NovaSeq platform.

RESULTS

The analysis demonstrated a higher prevalence of virulence genes compared to resistance and regulatory genes. Key virulence factors identified included secretion systems, motility, adhesion, and biofilm formation. Resistance mechanisms observed comprised efflux pumps and beta-lactamases, while regulatory systems involved two-component systems, transcriptional regulators, and sigma factors. Additionally, phenotypic profiles were found to correlate with resistance genes identified through genotypic analysis.

CONCLUSIONS

This study underscores the significant resistance and virulence of the clinical P. aeruginosa strains analyzed, highlighting the urgent need for alternative strategies to address infections caused by extensively drug-resistant bacteria.

A three-way junction probe triggered CRISPR/Cas14a1 enhanced EXPonential amplification reaction for sensitive Pseudomonas aeruginosa detection

Pseudomonas aeruginosa (P. aeruginosa, PA) is a rod-shaped Gram-negative opportunistic bacterium capable of causing nosocomial infections during nursing, such as burn wound infections and meningitis. However, sensitive and rapid PA detection remains a huge challenge. Herein, a new fluorescent biosensor was developed for the sensitive detection of PA using a three-way junction (TWJ) probe for specific identification and CRISPR/Cas14a1 for enhanced exponential amplification. The interaction between PA and its aptamer on a DNA TWJ structure probe triggered the migration of the double-stranded DNA branch, inducing DNA polymerase/endonuclease assisted chain displacement and the generation of single-stranded DNA sequences. The amplification products have the ability to activate CRISPR/Cas14a1, resulting in effective trans-cleavage and the subsequent release of fluorescence from the reporter probes. Under optimized conditions, the proposed biosensor was able to detect a wide range of bacterial concentrations, ranging from 10 to 105 cfu mL-1 within 30 min. The limit of detection, which is the lowest concentration that can be reliably detected, was determined to be 3.4 cfu mL-1 according to the 3δ rule. The results of the recovery test suggest that the biosensor shows significant potential for clinical applications. The established biosensor utilizing the TWJ probe generated multiple isothermal exponential amplification and the CRISPR/Cas14a1 biosensor is an excellent platform for rapidly detecting pathogenic bacteria in postoperative infection.

Clinical characteristics and gene analysis in 7 Chinese children with cystic fibrosis

BACKGROUND

Cystic fibrosis (CF) is common genetic disorder in Europe and North America but rarer in Asian populations.

OBJECTIVE

To explore the clinical manifestations and gene mutations of cystic fibrosis.

METHODS

This case series study enrolled children with CF diagnosed in the pediatric respiratory department of Shandong Provincial Hospital affiliated to Shandong First Medical University between June 2016 and August 2022.

RESULTS

Seven children, including 6 girls and 1 boy, were enrolled. All 7 patients had recurrent wet cough and (chronic) pneumonia. Six patients suffered from chronic sinusitis, 4 patients had recurrent wheezing; 2 patients had chronic diarrhea, malnutrition and growth lag; 2 patients were complicated by allergic bronchopulmonary aspergillosis; and 1 patient had pancreatic insufficiency. Bronchiectasis, thickening of bronchial wall and mucous impaction, were seen in the chest CT of 7 children. Six patients showed a large amount of viscous sputum adhered to the bronchial wall by bronchoscopy. Infection of Pseudomonas aeruginosa was found in 6 cases, Staphylococcus aureus in 2 cases, and Aspergillus fumigatus in 2 cases by bronchoalveolar lavage fluid or sputum culture. Sweat sodium chloride test was performed in 3 cases, and the result showed that Cl-> 60 mmol/L. CFTR gene mutations were found in 7 cases, which were rare mutations of Caucasians, including 2 cases with new mutation sites (c.325T>G and 326A>G).

CONCLUSIONS

The major clinical presentations of CF could be chronic and recurrent upper and lower respiratory tract infections, malnutrition, and digestive tract diseases. The rare and even new mutations of Caucasians on CFTR gene may occur in Chinese children.

Regulatory dynamics of arginine metabolism in Staphylococcus aureus

Staphylococcus aureus is a highly significant pathogen with several well studied and defined virulence factors. However, the metabolic pathways that are required to facilitate infection are not well described. Previous data have documented that S. aureus requires glucose catabolism during initial stages of infection. Therefore, certain nutrients whose biosynthetic pathway is under carbon catabolite repression and CcpA, including arginine, must be acquired from the host. However, even though S. aureus encodes pathways to synthesize arginine, biosynthesis of arginine is repressed even in the absence of glucose. Why is S. aureus a functional arginine auxotroph? This review discusses recently described regulatory mechanisms that are linked to repression of arginine biosynthesis using either proline or glutamate as substrates. In addition, recent studies are discussed that shed insight into the ultimate mechanisms linking arginine auxotrophy and infection persistence.

Eradication of Pseudomonas aeruginosa Persister Cells by Eravacycline

Pseudomonas aeruginosa is a leading bacterial pathogen that causes persistent infections. One major reason that antibiotics fail to clear such infections is the presence of a dormant subpopulation called persister cells. To eradicate persister cells, it is important to change drug development from traditional strategies that focus on growth inhibition to the search for new leads that can kill dormant cells. In this study, we demonstrate that eravacycline can effectively accumulate in P. aeruginosa persister cells, leading to strong killing during wakeup, including persister cells in both planktonic cultures and biofilms of the wild-type strain and its mucoid mutant. The effects of eravacycline on persister control were further validated in vivo using a lung infection model in mice. Collectively, these results demonstrate the possibility to control persister cells of bacterial pathogens by targeting dormancy.

Synergistic combinations of novel polymyxins and rifampicin with improved eradication of colistin-resistant Pseudomonas aeruginosa biofilms

Background

Increased prevalence of antimicrobial resistance coupled with a lack of new antibiotics against Gram-negative bacteria emphasize the imperative for novel therapeutic strategies. Colistin-resistant Pseudomonas aeruginosa constitutes a challenge, where conventional treatment options lack efficacy, in particular for biofilm-associated infections. Previously, synergy of colistin with other antibiotics was explored as an avenue for the treatment of colistin-resistant infections, and recently we reported our efforts towards colistin analogs capable of combating planktonic colistin-resistant strains.

Aims

The aim of the present study was to investigate whether analogs of polymyxin B with improved potency in wild-type and moderate resistant Gram-negative pathogens would retain similarly increased activity in highly colistin-resistant clinical P. aeruginosa isolates (in planktonic and biofilm growth) when applied alone and in combination with rifampicin.

Materials and methods

In this in vitro study, we tested three analogs of polymyxin B prepared by solid-phase peptide synthesis. Antimicrobial susceptibility testing was performed by measurement of minimum inhibitory concentrations via the broth microdilution method. Interactions between two antimicrobials was quantified in a checkerboard broth microdilution assay by calculating the fractional inhibitory concentration index for each combination. For testing of antibiofilm activity a previously described model with alginate beads encapsulating a biofilm culture was applied. The minimum biofilm eradication concentrations (MBECs) were evaluated, and the fractional biofilm eradication concentration indices were calculated. Three recently identified colistin analogs (CEP932, CEP936 and CEP938) were tested against three isogenic pairs of colistin-susceptible and colistin-resistant P. aeruginosa clinical isolates as well as the reference strain PAO1.

Results

For bacteria in planktonic growth CEP938 retained almost full potency in all three resistant isolates, while exhibiting similar activity as colistin in susceptible isolates. Against biofilms CEP938 was slightly more potent against PAO1 as compared to colistin, while also retaining activity against a biofilm of the colistin-resistant strain 41,782/98. Next, synergy between CEP938 and the antibiotic rifampicin was explored. Interestingly, CEP938 did not exhibit synergy with rifampicin in planktonic cultures. Importantly, for colistin-resistant biofilms the CEP938-rifampicin combination demonstrated activity superior to that found for the colistin-rifampicin combination.

Conclusions

The present study showed in vitro efficacy of CEP938 against both colistin-susceptible and colistin-resistant P. aeruginosa biofilms as well as an ability of CEP938 to synergize with rifampicin in biofilm eradication.

Pseudomonas aeruginosa faces a fitness trade-off between mucosal colonization and antibiotic tolerance during airway infection

Pseudomonas aeruginosa frequently causes antibiotic-recalcitrant pneumonia, but the mechanisms driving its adaptation during human infections remain unclear. To reveal the selective pressures and adaptation strategies at the mucosal surface, here we investigated P. aeruginosa growth and antibiotic tolerance in tissue-engineered airways by transposon insertion sequencing (Tn-seq). Metabolic modelling based on Tn-seq data revealed the nutritional requirements for P. aeruginosa growth, highlighting reliance on glucose and lactate and varying requirements for amino acid biosynthesis. Tn-seq also revealed selection against biofilm formation during mucosal growth in the absence of antibiotics. Live imaging in engineered organoids showed that biofilm-dwelling cells remained sessile while colonizing the mucosal surface, limiting nutrient foraging and reduced growth. Conversely, biofilm formation increased antibiotic tolerance at the mucosal surface. Moreover, mutants with exacerbated biofilm phenotypes protected less tolerant but more cytotoxic strains, contributing to phenotypic heterogeneity. P. aeruginosa must therefore navigate conflicting physical and biological selective pressures to establish chronic infections.

Progress in the study of mefloquine as an antibiotic adjuvant for combination bacterial inhibition treatment

Antimicrobial resistance is among the greatest threats to public health globally, and drug repurposing strategies may be advantageous to addressing this problem. Mefloquine, a drug traditionally used to treat malaria, has emerged as a promising antibiotic adjuvant, due to its ability to enhance the effectiveness of conventional antibiotics against resistant bacterial strains. In this paper, we first outline the enhancement properties of mefloquine and its mechanisms of action as an adjuvant antibiotic against multidrug-resistant bacteria. Mefloquine exhibits synergistic bacteriostatic effects when combined with colistin, β-lactams, antituberculosis drugs, quinolones, and linezolid. Potential mechanisms underlying its synergistic effects include inhibition of antibiotic efflux, disruption of bacterial cell membrane integrity, and disturbance of biofilm formation. In addition, we explore the bacteriostatic effects of several mefloquine derivatives against Mycobacterium tuberculosis and some fungi. Further, we summarize the findings of recent studies on other aspects of mefloquine activity, including its antiviral and antitumor effects. Finally, the advantages and challenges of mefloquine use as an antibiotic adjuvant in combination with antibiotics for bacterial inhibition are discussed. Overall, mefloquine shows excellent potential as an antibiotic adjuvant therapy against multidrug-resistant bacteria and is a promising candidate for combination therapy; however, further studies are needed to fully elucidate its mechanism of action and address the challenges associated with its clinical application.