Evolution of lasR mutants in polymorphic Pseudomonas aeruginosa populations facilitates chronic infection of the lung

Multifaceted quorum-sensing inhibiting activity of 3-(Benzo[d][1,3]dioxol-4-yl)oxazolidin-2-one mitigates Pseudomonas aeruginosa virulence

As antibiotic resistance escalates into a global health crisis, novel therapeutic approaches against infectious diseases are in urgent need. Pseudomonas aeruginosa, an adaptable opportunistic pathogen, poses substantial challenges in treating a range of infections. The quorum-sensing (QS) system plays a pivotal role in orchestrating the production of a large set of virulence factors in a cell density-dependent manner, and the anti-virulence strategy targeting QS may show huge potential. Here, we present a comprehensive investigation into the potential of the synthesized compound 3-(benzo[d][1,3]dioxol-4-yl)oxazolidin-2-one (OZDO, C10H9NO4) as a QS inhibitor to curb the virulence of P. aeruginosa. By employing an integrated approach encompassing in silico screening, in vitro and in vivo functional identification, we elucidated the multifaceted effects of OZDO. Molecular docking predicted that OZDO interfered with three core regulatory proteins of P. aeruginosa QS system. Notably, OZDO exhibited significant inhibition on the production of pyocyanin, rhamnolipid and extracellular proteases, biofilm formation, and cell motilities of P. aeruginosa. Transcriptomic analysis and quantitative real-time PCR displayed the down-regulation of QS-controlled genes in OZDO-treated PAO1, reaffirming the QS-inhibition activity of OZDO. In vivo assessments using a Caenorhabditis elegans-infection model demonstrated OZDO mitigated P. aeruginosa pathogenicity, particularly against the hypervirulent strain PA14. Moreover, OZDO in combination with polymyxin B and aztreonam presented a promising avenue for innovative anti-infective therapy. Our study sheds light on the multifaceted potential of OZDO as an anti-virulence agent and its significance in combating P. aeruginosa-associated infections.

Inhibitors of the PqsR Quorum-Sensing Receptor Reveal Differential Roles for PqsE and RhlI in Control of Phenazine Production

Pseudomonas aeruginosa is a leading cause of hospital-acquired infections and it is resistant to many current antibiotic therapies, making development of new antimicrobial treatments imperative. The cell-to-cell communication process called quorum sensing controls P. aeruginosa pathogenicity. Quorum sensing relies on the production, release, and group-wide detection of extracellular signal molecules called autoinducers. Quorum sensing enables bacteria to synchronize group behaviors. P. aeruginosa possesses multiple quorum-sensing systems that control overlapping regulons, including some required for virulence and biofilm formation. Interventions that target P. aeruginosa quorum-sensing receptors are considered a fruitful avenue to pursue for new therapeutic advances. Here, we developed a P. aeruginosa strain that carries a bioluminescent reporter fused to a target promoter that is controlled by two P. aeruginosa quorum-sensing receptors. The receptors are PqsR, which binds and responds to the autoinducer called PQS (2-heptyl-3-hydroxy-4(1H)-quinolone) and RhlR, which binds and responds to the autoinducer called C4-HSL (C4-homoserine lactone). We used this reporter strain to screen >100,000 compounds with the aim of identifying inhibitors of either or both the PqsR and RhlR quorum-sensing receptors. We report results for 30 PqsR inhibitors from this screen. All of the identified compounds inhibit PqsR with IC50 values in the nanomolar to low micromolar range and they are readily docked into the autoinducer binding site of the PqsR crystal structure, suggesting they function competitively. The majority of hits identified are not structurally related to previously reported PqsR inhibitors. Recently, RhlR was shown to rely on the accessory protein PqsE for full function. Specifically, RhlR controls different subsets of genes depending on whether or not it is bound to PqsE, however, the consequences of differential regulation on the quorum-sensing output response have not been defined. PqsR regulates pqsE. That feature of the system enabled us to exploit our new set of PqsR inhibitors to show that RhlR requires PqsE to activate the biosynthetic genes for pyocyanin, a key P. aeruginosa virulence factor, while C4-HSL is dispensable. These results highlight the promise of inhibition of PqsR as a possible P. aeruginosa therapeutic to suppress production of factors under RhlR-PqsE control.

Phage-host interaction in Pseudomonas aeruginosa clinical isolates with functional and altered quorum sensing systems

Quorum sensing (QS) plays a crucial role in regulating key traits, including the upregulation of phage receptors, which leads to heightened phage susceptibility in Pseudomonas aeruginosa. As a result, higher cell densities typically increase the risk of phage invasions. This has led to speculation that bacteria may have evolved strategies to counterbalance this increased susceptibility. Additionally, non-synonymous mutations in LasR, the master regulator of QS, are common among cystic fibrosis patients, but the impact of these mutations on phage interactions remains poorly understood. Here, we systematically investigated the role of QS in shaping these interactions using bacterial strains with functional or altered QS systems. In the QS-functional strain ZS-PA-35, disruption of the Las system reduces cell susceptibility to the type IV pili-dependent phage phipa2, delaying bacterial lysis during the early logarithmic growth phase. At high cell densities, Las-induced dormancy further inhibits phage proliferation despite enhanced phage adsorption. Notably, nutrient supplementation fully restores phage proliferation in the strains with a functional Las system. In contrast, the QS-deficient strain ZS-PA-05, carrying a LasR mutation, fails to regulate phage-host interactions via QS. Moreover, our findings reveal that within mixed microbial populations, cells benefit from the presence of closely related kin, which collectively reduce prey density and limit phage-host interaction frequencies under nutrient-rich conditions. These results underscore the flexibility of QS-regulated defense strategies, highlighting their critical role in optimizing bacterial resilience against phage predation, particularly in heterogeneous communities most vulnerable to phages.IMPORTANCEBacteria have developed various strategies to combat phage infection, posing challenges to phage therapy. In this study, we demonstrate that Pseudomonas aeruginosa strains with functional or altered quorum sensing (QS) systems may adapt different survival tactics for prolonged coexistence with phages, contingent upon bacterial population dynamics. The dynamics of phage infection highlight the influence of intrinsic heterogeneity mediated by QS, which leads to the emergence of different phage-host outcomes. These variants may arise as a result of coevolutionary processes or coexistence mechanisms of mutational and non-mutational defense strategies. These insights enhance our comprehension of how bacteria shield themselves against phage attacks and further underscore the complexity of such approaches for successful therapeutic interventions.

Antibiotic-Resistant Pseudomonas aeruginosa: Current Challenges and Emerging Alternative Therapies

Antibiotic-resistant Pseudomonas aeruginosa is a pathogen notorious for its resilience in clinical settings due to biofilm formation, efflux pumps, and the rapid acquisition of resistance genes. With traditional antibiotic therapy rendered ineffective against Pseudomonas aeruginosa infections, we explore alternative therapies that have shown promise, including antimicrobial peptides, nanoparticles and quorum sensing inhibitors. While these approaches offer potential, they each face challenges, such as specificity, stability, and delivery, which require careful consideration and further study. We also delve into emerging alternative strategies, such as bacteriophage therapy and CRISPR-Cas gene editing that could enhance targeted treatment for personalized medicine. As most of them are currently in experimental stages, we highlight the need for clinical trials and additional research to confirm their feasibility. Hence, we offer insights into new therapeutic avenues that could help address the pressing issue of antibiotic-resistant Pseudomonas aeruginosa, with an eye toward practical applications in future healthcare.

Development and Characterization of LasR Immobilized Monolithic Column for Screening Active Ingredients as Quorum Sensing Inhibitors Against P. aeruginosa in Natural Products

Background and Aim

The enzyme/protein immobilized monolithic capillary combined with liquid chromatography-mass spectrometry is an efficient screening strategy for the corresponding agonist/antagonist. LasR is the potential therapeutic target since it plays a vital role in the colonization and invasion of Pseudomonas aeruginosa (P. aeruginosa). Therefore, reagents that inhibit LasR may be effective against P. aeruginosa. To screen and find LasR inhibitors rapidly, a LasR-immobilized monolithic capillary column was prepared and characterized.

Methods

Firstly, the recombinant LasR protein was prepared in E. coli. Then, the LasR protein was immobilized to the surface of poly (glycidyl methacrylate-co-poly(ethylene glycol)diacrylate)-ethylenediamine monolithic column. The affinity and stability of prepared column was also evaluated. Furthermore, the prepared column was applied to fishing LasR inhibitor in Scutellaria baicalensis Georgi extract. The interaction of the screening compound to LasR was confirmed through molecular docking.

Results

The recombinant active LasR protein was prepared in E. coli. After purification and validation, a comparative ligand fishing monolithic column was prepared through immobilizing LasR to the surface of the poly (glycidyl methacrylate-co-poly(ethylene glycol)diacrylate)-ethylenediamine through amidation reaction. The LasR was successfully immobilized to the monolithic column characterizing by Fourier transform infrared spectroscopy and scanning electron microscopy. The activity of immobilized LasR was reserved as it has affinity to the nature ligand 3-oxo-C12-HSL and stablied within 24 h at 4 °C. In the Scutellaria baicalensis Georgi extract, baicalein was screened as a potential LasR inhibitor. The molecular docking results and the in vivo evaluation confirmed the activity of baicalein.

Conclusion

The proposed LasR immobilized monolithic column is a viable strategy in screening LasR inhibitors. It can be considered as a possible alternative to traditional methods for screening LasR inhibitors as drug candidates against P. aeruginosa.

Inhibitors of the PqsR Quorum-Sensing Receptor Reveal Differential Roles for PqsE and RhlI in Control of Phenazine Production

Pseudomonas aeruginosa is a leading cause of hospital-acquired infections and it is resistant to many current antibiotic therapies, making development of new anti-microbial treatments imperative. The cell-to-cell communication process called quorum sensing controls P. aeruginosa pathogenicity. Quorum sensing relies on the production, release, and group-wide detection of extracellular signal molecules called autoinducers. Quorum sensing enables bacteria to synchronize group behaviors. P. aeruginosa possesses multiple quorum-sensing systems that control overlapping regulons, including those required for virulence and biofilm formation. Interventions that target P. aeruginosa quorum-sensing receptors are considered a fruitful avenue to pursue for new therapeutic advances. Here, we developed a P. aeruginosa strain that carries a bioluminescent reporter fused to a target promoter that is controlled by two P. aeruginosa quorum-sensing receptors. The receptors are PqsR, which binds and responds to the autoinducer called PQS (2-heptyl-3-hydroxy-4(1H)-quinolone) and RhlR, which binds and responds to the autoinducer called C4-HSL (C4-homoserine lactone). We used this reporter strain to screen >100,000 compounds with the aim of identifying inhibitors of either or both the PqsR and RhlR quorum-sensing receptors. We report results for 30 PqsR inhibitors from this screen. All of the identified compounds inhibit PqsR with IC50 values in the nanomolar to low micromolar range and they are readily docked into the autoinducer binding site of the PqsR crystal structure, suggesting they function competitively. The majority of hits identified are not structurally related to previously reported PqsR inhibitors. Recently, RhlR was shown to rely on the accessory protein PqsE for full function. Specifically, RhlR controls different subsets of genes depending on whether it is bound to PqsE or to C4-HSL, however, the consequences of differential regulation on the quorum-sensing output response have not been defined. PqsR regulates pqsE. That feature of the system enabled us to exploit our new set of PqsR inhibitors to show that RhlR requires PqsE to activate the biosynthetic genes for pyocyanin, a key P. aeruginosa virulence factor, while C4-HSL is dispensable. These results highlight the promise of inhibition of PqsR as a possible P. aeruginosa therapeutic to suppress production of factors under RhlR-PqsE control.

Moxifloxacin-Loaded Polymeric Nanoparticles for Overcoming Multidrug Resistance in Chronic Pulmonary Infections Caused by Pseudomonas aeruginosa

Pseudomonas aeruginosa (P. aeruginosa) infections are increasingly challenging due to their propensity to form biofilms and low outer membrane permeability, especially in chronically infected patients with thick mucus. P. aeruginosa exhibits multiple drug resistance mechanisms, making it one of the most significant global public health threats. In this study, we found that moxifloxacin (MXC) and antibacterial peptides (ε-poly-l-lysine, ε-PLL) exhibited a synergistic effect against multidrug-resistant P. aeruginosa (MDR-P. aeruginosa). MXC was combined with ε-PLL to prepare lipase-responsive nanoparticles (MCIP/(PEG-PCL)/PLL NPs) with a weakly negative charge. The weakly negatively charged MCIP/(PEG-PCL)/PLL NPs demonstrated remarkable mucus and biofilm penetration capabilities, thereby overcoming one of the adaptive drug resistance mechanisms. MCIP/(PEG-PCL)/PLL NPs improved the outer and inner membrane permeability and inhibited the expression of the efflux pump MexAB-OprM gene in MDR-P. aeruginosa, thereby overcoming mechanisms of both intrinsic and acquired drug resistance. Meanwhile, the nanoparticles demonstrated an ability to reduce repeated infections with MDR-P. aeruginosa. Additionally, the bacterial burden in the lungs of mice treated with MCIP/(PEG-PCL)/PLL NPs was significantly lower than that in the MXC group, resulting in a 99% clearance rate. Notably, MCIP/(PEG-PCL)/PLL NPs showed no toxicity toward BEAS-2B cells or RAW 267.4 cells, nor did they adversely affect pulmonary function or major organs. This study demonstrated the potential of the nanodrug delivery system composed of the antibiotic moxifloxacin and the antibacterial peptide ε-PLL in addressing the clinical challenges of treating chronic pulmonary infections caused by MDR-P. aeruginosa.

Revealing quorum-sensing networks in Pseudomonas aeruginosa infections through internal and external signals to prevent new resistance trends

In the context of growing antibiotic resistance in bacteria, the quorum-sensing (QS) system of Pseudomonas aeruginosa (P. aeruginosa) has become a target for new therapeutic strategies. QS is a crucial communication process and an essential pathogenic mechanism. This comprehensive review explores the critical role of QS in the pathogenesis of P. aeruginosa infections, including lung, burn, bloodstream, gastrointestinal, corneal, and urinary tract infections. In addition, this review delves into the complexity of the bacterial QS communication network and highlights the intricate mechanisms underlying these pathological processes. Notably, in addition to the four main QS systems, bacterial QS can interact with various external and internal signaling networks, such as host environments and nutrients in the external microbiome, as well as internal virulence regulation systems within bacteria. These elements can significantly influence the behavior and virulence of microbial communities. Therefore, this review reveals that inhibitors targeting singular QS pathways may inadvertently promote virulence in other pathways, leading to new trends in drug resistance. In response to evolving resistance challenges, this study proposes more cautious treatment strategies, including multitarget interventions and combination therapies, aimed at combating the escalating issue of resistance.

Isovanillin decreases the virulence regulated by the quorum sensing system of Pseudomonas aeruginosa

The quorum-sensing (QS) system of Pseudomonas aeruginosa dominates the pathogenicity of the acute or chronic infection process. Hence, curbing the pathogenicity of P. aeruginosa by targeting QS system is an ideal strategy. This study aims to identify potential anti-virulence compounds that can effectively disrupt the QS system of P. aeruginosa using a combination of virtual screening and experimental validation techniques. We explored inhibitory effect of isovanillin obtained by virtual screening on P. aeruginosa QS regulated virulence factors extracellular protease, biofilm, and pyocyanin. Results displayed that isovanillin could inhibit the virulence phenotypes regulated by the las- and pqs-QS systems of P. aeruginosa. The synthesis of extracellular proteases, pyocyanin, and biofilm formation by P. aeruginosa were dramatically inhibited by sub-MICs doses of isovanillin. The results of RNA sequencing and quantitative PCR revealed that the QS-activated genes down-regulated by subinhibitory isovanillin in the transcriptional evels. Furthermore, the presence of isovanillin increased the susceptibility of drug-resistant P. aeruginosa to kanamycin, meropenem, and polymyxin B. Treatment of isovanillin as a monotherapy significantly decreased the mortality of C. elegans in P. aeruginosa PAO1 or UCBPP-PA14 (PA14) infection. Our study reported the anti-virulence activity of isovanillin against P. aeruginosa, and provided a structural foundation for developing anti-virulence drugs targeting the QS system of P. aeruginosa.

Mutation of Pseudomonas aeruginosa lasI/rhlI diminishes its cytotoxicity, oxidative stress, inflammation, and apoptosis on THP-1 macrophages

The management of Pseudomonas aeruginosa (P. aeruginosa) infections presents a substantial challenge to clinics and public health, emphasizing the urgent need for innovative strategies to address this issue. Quorum sensing (QS) is an intercellular communication mechanism that coordinates bacterial activities involved in various virulence mechanisms, such as acquiring host nutrients, facilitating biofilm formation, enhancing motility, secreting virulence factors, and evading host immune responses, all of which play a crucial role in the colonization and infection of P. aeruginosa. The LasI/R and RhlI/R sub-systems dominate in the QS system of P. aeruginosa. Macrophages play a pivotal role in the host's innate immune response to P. aeruginosa invasion, particularly through phagocytosis as the initial host defense mechanism. This study investigated the effects of P. aeruginosa's QS system on THP-1 macrophages. Mutants of PAO1 with lasI/rhlI deletion, as well as their corresponding complemented strains, were obtained, and significant downregulation of QS-related genes was observed in the mutants. Furthermore, the ΔlasI and ΔlasIΔrhlI mutants exhibited significantly attenuated virulence in terms of biofilm formation, extracellular polymeric substances synthesis, bacterial adhesion, motility, and virulence factors production. When infected with ΔlasI and ΔlasIΔrhlI mutants, THP-1 macrophages exhibited enhanced scavenging ability against the mutants and demonstrated resistance to cytotoxicity, oxidative stress, inflammatory response, and apoptosis induced by the culture supernatants of these mutant strains. These findings offer novel insights into the mechanisms underlying how the lasI/rhlI mutation attenuates cytotoxicity, oxidative stress, inflammation, and apoptosis in macrophages induced by P. aeruginosa.IMPORTANCEP. aeruginosa is classified as one of the ESKAPE pathogens and poses a global public health concern. The QS system of this versatile pathogen contributes to a broad spectrum of virulence, thereby constraining therapeutic options for serious infections. This study illustrated that the lasI/rhlI mutation of the QS system plays a prominent role in attenuating the virulence of P. aeruginosa by affecting bacterial adhesion, biofilm formation, extracellular polymeric substances synthesis, bacterial motility, and virulence factors' production. Notably, THP-1 macrophages infected with mutant strains exhibited increased phagocytic activity in eliminating intracellular bacteria and enhanced resistance to cytotoxicity, oxidative stress, inflammation, and apoptosis. These findings suggest that targeted intervention toward the QS system is anticipated to diminish the pathogenicity of P. aeruginosa to THP-1 macrophages.

Harmine acts as a quorum sensing inhibitor decreasing the virulence and antibiotic resistance of Pseudomonas aeruginosa

BACKGROUND

As antimicrobial resistance (AMR) has become a global health crisis, new strategies against AMR infection are urgently needed. Quorum sensing (QS), responsible for bacterial communication and pathogenicity, is among the targets for anti-virulence drugs that thrive as one of the promising treatments against AMR infection.

METHODS

We identified a natural compound, Harmine, through virtual screening based on three QS receptors of Pseudomonas aeruginosa (P. aeruginosa) and explored the effect of Harmine on QS-controlled and pathogenicity-related phenotypes including pyocyanin production, exocellular protease excretion, biofilm formation, and twitching motility of P. aeruginosa PA14. The protective effect of Harmine on Caenorhabditis elegans (C. elegans) and mice infection models was determined and the synergistic effect of Harmine combined with common antibiotics was explored. The underlaying mechanism of Harmine's QS inhibitory effect was illustrated by molecular docking analysis, transcriptomic analysis, and target verification assay.

RESULTS

In vitro results suggested that Harmine possessed QS inhibitory effects on pyocyanin production, exocellular protease excretion, biofilm formation, and twitching motility of P. aeruginosa PA14, and in vivo results displayed Harmine's protective effect on C. elegans and mice infection models. Intriguingly, Harmine increased susceptibility of both PA14 and clinical isolates of P. aeruginosa to polymyxin B and kanamycin when used in combination. Moreover, Harmine down-regulated a series of QS controlled genes associated with pathogenicity and the underlying mechanism may have involved competitively antagonizing autoinducers' receptors LasR, RhlR, and PqsR.

CONCLUSIONS

This study shed light on the anti-virulence potential of Harmine against QS targets, suggesting the possible use of Harmine and its derivates as anti-virulence compounds.

The evolution of antimicrobial peptide resistance in Pseudomonas aeruginosa is severely constrained by random peptide mixtures

The prevalence of antibiotic-resistant pathogens has become a major threat to public health, requiring swift initiatives for discovering new strategies to control bacterial infections. Hence, antibiotic stewardship and rapid diagnostics, but also the development, and prudent use, of novel effective antimicrobial agents are paramount. Ideally, these agents should be less likely to select for resistance in pathogens than currently available conventional antimicrobials. The usage of antimicrobial peptides (AMPs), key components of the innate immune response, and combination therapies, have been proposed as strategies to diminish the emergence of resistance. Herein, we investigated whether newly developed random antimicrobial peptide mixtures (RPMs) can significantly reduce the risk of resistance evolution in vitro to that of single sequence AMPs, using the ESKAPE pathogen Pseudomonas aeruginosa (P. aeruginosa) as a model gram-negative bacterium. Infections of this pathogen are difficult to treat due the inherent resistance to many drug classes, enhanced by the capacity to form biofilms. P. aeruginosa was experimentally evolved in the presence of AMPs or RPMs, subsequentially assessing the extent of resistance evolution and cross-resistance/collateral sensitivity between treatments. Furthermore, the fitness costs of resistance on bacterial growth were studied and whole-genome sequencing used to investigate which mutations could be candidates for causing resistant phenotypes. Lastly, changes in the pharmacodynamics of the evolved bacterial strains were examined. Our findings suggest that using RPMs bears a much lower risk of resistance evolution compared to AMPs and mostly prevents cross-resistance development to other treatments, while maintaining (or even improving) drug sensitivity. This strengthens the case for using random cocktails of AMPs in favour of single AMPs, against which resistance evolved in vitro, providing an alternative to classic antibiotics worth pursuing.

The end of the reign of a "master regulator''? A defect in function of the LasR quorum sensing regulator is a common feature of Pseudomonas aeruginosa isolates

Pseudomonas aeruginosa, a bacterium causing infections in immunocompromised individuals, regulates several of its virulence functions using three interlinked quorum sensing (QS) systems (las, rhl, and pqs). Despite its presumed importance in regulating virulence, dysfunction of the las system regulator LasR occurs frequently in strains isolated from various environments, including clinical infections. This newfound abundance of LasR-defective strains calls into question existing hypotheses regarding their selection. Indeed, current assumptions concerning factors driving the emergence of LasR-deficient isolates and the role of LasR in the QS hierarchy must be reconsidered. Here, we propose that LasR is not the primary master regulator of QS in all P. aeruginosa genetic backgrounds, even though it remains ecologically significant. We also revisit and complement current knowledge on the ecology of LasR-dependent QS in P. aeruginosa, discuss the hypotheses explaining the putative adaptive benefits of selecting against LasR function, and consider the implications of this renewed understanding.

Phenotypic heterogeneity unveils a negative correlation between antibiotic resistance and quorum sensing in Pseudomonas aeruginosa clinical isolates

Colonization of Pseudomonas aeruginosa in the lung environments frequently leads to the enrichment of strains displaying enhanced antibiotic resistance and reduced production of quorum-sensing (QS) controlled products. However, the relationship between the emergence of QS deficient variants and antibiotic resistance remains less understood. In this study, 67 P. aeruginosa strains were isolated from the lungs of 14 patients with chronic obstructive pulmonary disease, followed by determining their genetic relationship, QS-related phenotypes and resistance to commonly used antibiotics. The integrity of P. aeruginosa QS system was checked by DNA sequencing. The relationship between the QS system and antibiotic resistance was then assessed by correlation analyses. The function of the LasR protein and bacterial virulence were evaluated through homology modeling and nematode-infection assay. The influence of antibiotic on the development of extracellular protease production ability of P. aeruginosa was tested by an evolutionary experiment. The results showed that P. aeruginosa clinical strains displayed abundant diversity in phenotype and genotype. The production of extracellular proteases was significantly negatively correlated with antibiotic resistance. The strains with enhanced antibiotic resistance also showed a notable overlap with the mutation of lasR gene, which is the core regulatory gene of P. aeruginosa QS system. Molecular docking and Caenorhabditis elegans infection assays further suggested that P. aeruginosa with impaired LasR protein could also have varying pathogenicity. Moreover, in vitro evolution experiments demonstrated that antibiotic-mediated selective pressure, particularly from Levofloxacin contributed to the emergence of extracellular protease-negative strains. Therefore, this study provides evidence for the connection of P. aeruginosa QS system and antibiotic resistance, and holds significance for developing targeted strategies to address antibiotic resistance and improving the management of antibiotic-resistant infections in chronic respiratory diseases.

Phylogenetic evaluation and genotypic identification of burn-related Pseudomonas aeruginosa strains isolated from post-burn human infections during hospitalization

Cutaneous burn trauma, compromise of dermal layers and immune defense system is a physical and fiscal burden on healthcare systems. Burn-wound infections are a serious complication of thermal injury and contribute significantly to care burden. After burn-induced trauma, sepsis by Pseudomonas aeruginosa impairs patient recovery and contributes to mortality and morbidity. Past studies show positive correlation between detection of Pseudomonas species and healing-impaired traumatic wounds. Pseudomonas aeruginosa is a resilient opportunistic human pathogen and a nosocomial agent involved in pathology of healing-impaired wounds, especially in burn patients. Expansive array of virulence determinants has resulted in gentamicin- and silver-resistant P. aeruginosa outbreaks. Knowledge of molecular dynamics and phylogeny of P. aeruginosa associated with burn wounds is limited. Therefore, we conducted whole-genome sequencing for genotyping and phylogenetic analysis of P. aeruginosa burn-associated strains (n = 19) isolated from 7 burn cases during hospitalization. Comparison of genetic features in P. aeruginosa strains in the core genome and mobilome detected genetic variations within some clonal infections over time. Genetic variations were observed among different burn cases, with some features identified in severe lung infections. Polyclonal infections were also observed, with differing genotypes and virulence potentials, highlighting the importance of reasoned sampling of isolates for clinical testing.

Metabarcoding Analysis of Microorganisms Inside Household Washing Machines in Shanghai, China

Washing machines are one of the tools that bring great convenience to people's daily lives. However, washing machines that have been used for a long time often develop issues such as odor and mold, which can pose health hazards to consumers. There exists a conspicuous gap in our understanding of the microorganisms that inhabit the inner workings of washing machines. In this study, samples were collected from 22 washing machines in Shanghai, China, including both water eluted from different parts of washing machines and biofilms. Quantitative qualitative analysis was performed using fluorescence PCR quantification, and microbial communities were characterized by high-throughput sequencing (HTS). This showed that the microbial communities in all samples were predominantly composed of bacteria. HTS results showed that in the eluted water samples, the bacteria mainly included Pseudomonas, Enhydrobacter, Brevibacterium, and Acinetobacter. Conversely, in the biofilm samples, Enhydrobacter and Brevibacterium were the predominant bacterial microorganisms. Correlation analysis results revealed that microbial colonies in washing machines were significantly correlated with years of use and the type of detergent used to clean the washing machine. As numerous pathogenic microorganisms can be observed in the results, effective preventive measures and future research are essential to mitigate these health problems and ensure the continued safe use of these household appliances.

Divergent molecular strategies drive evolutionary adaptation to competitive fitness in biofilm formation

Biofilm is a group of heterogeneously structured and densely packed bacteria with limited access to nutrients and oxygen. These intrinsic features can allow a mono-species biofilm to diversify into polymorphic subpopulations, determining the overall community's adaptive capability to changing ecological niches. However, the specific biological functions underlying biofilm diversification and fitness adaptation are poorly demonstrated. Here, we launched and monitored the experimental evolution of Pseudomonas aeruginosa biofilms, finding that two divergent molecular trajectories were adopted for adaptation to higher competitive fitness in biofilm formation: one involved hijacking bacteriophage superinfection to aggressively inhibit kin competitors, whereas the other induced a subtle change in cyclic dimeric guanosine monophosphate signaling to gain a positional advantage via enhanced early biofilm adhesion. Bioinformatics analyses implicated that similar evolutionary strategies were prevalent among clinical P. aeruginosa strains, indicative of parallelism between natural and experimental evolution. Divergence in the molecular bases illustrated the adaptive values of genomic plasticity for gaining competitive fitness in biofilm formation. Finally, we demonstrated that these fitness-adaptive mutations reduced bacterial virulence. Our findings revealed how the mutations intrinsically generated from the biofilm environment influence the evolution of P. aeruginosa.

Biofilm formation: mechanistic insights and therapeutic targets

Biofilms are complex multicellular communities formed by bacteria, and their extracellular polymeric substances are observed as surface-attached or non-surface-attached aggregates. Many types of bacterial species found in living hosts or environments can form biofilms. These include pathogenic bacteria such as Pseudomonas, which can act as persistent infectious hosts and are responsible for a wide range of chronic diseases as well as the emergence of antibiotic resistance, thereby making them difficult to eliminate. Pseudomonas aeruginosa has emerged as a model organism for studying biofilm formation. In addition, other Pseudomonas utilize biofilm formation in plant colonization and environmental persistence. Biofilms are effective in aiding bacterial colonization, enhancing bacterial resistance to antimicrobial substances and host immune responses, and facilitating cell‒cell signalling exchanges between community bacteria. The lack of antibiotics targeting biofilms in the drug discovery process indicates the need to design new biofilm inhibitors as antimicrobial drugs using various strategies and targeting different stages of biofilm formation. Growing strategies that have been developed to combat biofilm formation include targeting bacterial enzymes, as well as those involved in the quorum sensing and adhesion pathways. In this review, with Pseudomonas as the primary subject of study, we review and discuss the mechanisms of bacterial biofilm formation and current therapeutic approaches, emphasizing the clinical issues associated with biofilm infections and focusing on current and emerging antibiotic biofilm strategies.