A Pseudomonas aeruginosa PQS quorum-sensing system inhibitor with anti-staphylococcal activity sensitizes polymicrobial biofilms to tobramycin

Strategies for controlling polymicrobial biofilms: A focus on antibiofilm agents

Polymicrobial biofilms are among the leading causes of antimicrobial treatment failure. In these biofilms, bacterial and fungal pathogens interact synergistically at the interspecies, intraspecies, and interkingdom levels. Consequently, combating polymicrobial biofilms is substantially more difficult compared to single-species biofilms due to their distinct properties and the resulting potential variation in antimicrobial drug efficiency. In recent years, there has been an increased focus on developing alternative strategies for controlling polymicrobial biofilms formed by bacterial and fungal pathogens. Current approaches for controlling polymicrobial biofilms include monotherapy (using either natural or synthetic compounds), combination treatments, and nanomaterials. Here, a comprehensive review of different types of polymicrobial interactions between pathogenic bacterial species or bacteria and fungi is provided along with a discussion of their relevance. The mechanisms of action of individual compounds, combination treatments, and nanomaterials against polymicrobial biofilms are thoroughly explored. This review provides various future perspectives that can advance the strategies used to control polymicrobial biofilms and their likely modes of action. Since the majority of research on combating polymicrobial biofilms has been conducted in vitro, it would be an essential step in performing in vivo tests to determine the clinical effectiveness of different treatments against polymicrobial biofilms.

Nanocomposites against Pseudomonas aeruginosa biofilms: Recent advances, challenges, and future prospects

Pseudomonas aeruginosa is an opportunistic bacterial pathogen that causes life-threatening and persistent infections in immunocompromised patients. It is the culprit behind a variety of hospital-acquired infections owing to its multiple tolerance mechanisms against antibiotics and disinfectants. Biofilms are sessile microbial aggregates that are formed as a result of the cooperation and competition between microbial cells encased in a self-produced matrix comprised of extracellular polymeric constituents that trigger surface adhesion and microbial aggregation. Bacteria in biofilms exhibit unique features that are quite different from planktonic bacteria, such as high resistance to antibacterial agents and host immunity. Biofilms of P. aeruginosa are difficult to eradicate due to intrinsic, acquired, and adaptive resistance mechanisms. Consequently, innovative approaches to combat biofilms are the focus of the current research. Nanocomposites, composed of two or more different types of nanoparticles, have diverse therapeutic applications owing to their unique physicochemical properties. They are emerging multifunctional nanoformulations that combine the desired features of the different elements to obtain the highest functionality. This review assesses the recent advances of nanocomposites, including metal-, metal oxide-, polymer-, carbon-, hydrogel/cryogel-, and metal organic framework-based nanocomposites for the eradication of P. aeruginosa biofilms. The characteristics and virulence mechanisms of P. aeruginosa biofilms, as well as their devastating impact and economic burden are discussed. Future research addressing the potential use of nanocomposites as innovative anti-biofilm agents is emphasized. Utilization of nanocomposites safely and effectively should be further strengthened to confirm the safety aspects of their application.

Taming Pseudomonas aeruginosa AM26 the barbarian: Targeting the PQS quorum sensing network using crude mandarin extract

Pseudomonas aeruginosa, one of the most notorious organisms, causes fatal diseases like-, meningitis, pneumonia as well as worsens the prognosis of cystic fibrosis patients. It is also multi-drug resistant and resists a wide range of antibiotics. Attempts have been made to reduce its virulence/pathogenic potential using a number of organic compounds. For this purpose, the Quorum sensing (QS) system of P. aeruginosa was targeted, which regulates its virulence. Pseudomonas Quinolone System (PQS), one of the four quorum sensing systems, producing pyocyanin pigment was chosen. 2-heptyl-3-hydroxy-4-quinolone (HHQ) is a ligand which binds to PQS protein is responsible for pyocyanin pigment production. Attempts were made to find a compound analogous to HHQ which could bind to PQS active site and inhibit the pigment formation. In-silico analysis was performed to estimate possible interactions and to find/predict the possible PQS inhibitors.

Aptamer-based therapy for fighting biofilm-associated infections

Biofilms are key players in the pathogenesis of most of chronic infections associated with host tissue or fluids and indwelling medical devices. These chronic infections are hard to be treated due to the increased biofilms tolerance towards antibiotics in comparison to planktonic (or free living) cells. Despite the advanced understanding of their formation and physiology, biofilms continue to be a challenge and there is no standardized therapeutic approach in clinical practice to eradicate them. Aptamers offer distinctive properties, including excellent affinity, selectivity, stability, making them valuable tools for therapeutic purposes. This review explores the flexibility and designability of aptamers as antibiofilm drugs but, importantly, as targeting tools for diverse drug and delivery systems. It highlights specific examples of application of aptamers in biofilms of diverse species according to different modes of action including inhibition of motility and adhesion, blocking of quorum sensing molecules, and dispersal of biofilm-cells to planktonic state. Moreover, it discusses the limitations and challenges that impaired an increased success of the use of aptamers on biofilm management, as well as the opportunities related to aptamers modifications that can significantly expand their applicability on the biofilm field.

Molecular Aspects of the Functioning of Pathogenic Bacteria Biofilm Based on Quorum Sensing (QS) Signal-Response System and Innovative Non-Antibiotic Strategies for Their Elimination

One of the key mechanisms enabling bacterial cells to create biofilms and regulate crucial life functions in a global and highly synchronized way is a bacterial communication system called quorum sensing (QS). QS is a bacterial cell-to-cell communication process that depends on the bacterial population density and is mediated by small signalling molecules called autoinducers (AIs). In bacteria, QS controls the biofilm formation through the global regulation of gene expression involved in the extracellular polymeric matrix (EPS) synthesis, virulence factor production, stress tolerance and metabolic adaptation. Forming biofilm is one of the crucial mechanisms of bacterial antimicrobial resistance (AMR). A common feature of human pathogens is the ability to form biofilm, which poses a serious medical issue due to their high susceptibility to traditional antibiotics. Because QS is associated with virulence and biofilm formation, there is a belief that inhibition of QS activity called quorum quenching (QQ) may provide alternative therapeutic methods for treating microbial infections. This review summarises recent progress in biofilm research, focusing on the mechanisms by which biofilms, especially those formed by pathogenic bacteria, become resistant to antibiotic treatment. Subsequently, a potential alternative approach to QS inhibition highlighting innovative non-antibiotic strategies to control AMR and biofilm formation of pathogenic bacteria has been discussed.

Multidimensional Criteria for Virtual Screening of PqsR Inhibitors Based on Pharmacophore, Docking, and Molecular Dynamics

Pseudomonas aeruginosa is a clinically challenging pathogen due to its high resistance to antibiotics. Quorum sensing inhibitors (QSIs) have been proposed as a promising strategy to overcome this resistance by interfering with the bacterial communication system. Among the potential targets of QSIs, PqsR is a key regulator of quorum sensing in Pseudomonas aeruginosa. However, the current research on PqsR inhibitors is limited by the lack of diversity in the chemical structures and the screening methods. Therefore, this study aims to develop a multidimensional screening model for PqsR inhibitors based on both ligand- and receptor-based approaches. First, a pharmacophore model was constructed from a training set of PqsR inhibitors to identify the essential features and spatial arrangement for the activity. Then, molecular docking and dynamics simulations were performed to explore the core interactions between PqsR inhibitors and their receptor. The results indicate that an effective PqsR inhibitor should possess two aromatic rings, one hydrogen bond acceptor, and two hydrophobic groups and should form strong interactions with the following four amino acid residues: TYR_258, ILE_236, LEU_208, and GLN_194. Moreover, the docking score and the binding free energy should be lower than -8 kcal/mol and -40 kcal/mol, respectively. Finally, the validity of the multidimensional screening model was confirmed by a test set of PqsR inhibitors, which showed a higher accuracy than the existing screening methods based on single characteristics. This multidimensional screening model would be a useful tool for the discovery and optimization of PqsR inhibitors in the future.

The healing effect of Pseudomonas Quinolone Signal (PQS) with co-infection of Staphylococcus aureus and Pseudomonas aeruginosa: A preclinical animal co-infection model

BACKGROUND

Because of the rise in antibiotic resistance and the control of pathogenicity, polymicrobial bacterial biofilms exacerbate wound infections. Since bacterial quorum sensing (QS) signals can dysregulate biofilm development, they are interesting therapeutic treatments. In this study, Pseudomonas Quinolone Signal (PQS) was used to treat an animal model of a wound that had both Staphylococcus aureus and Pseudomonas aeruginosa co-infection.

METHODS

S. aureus and P. aeruginosa mono- and co-infection models were developed in vitro on the L-929 cell line and in an animal model of wound infection. Moreover, PQS was extracted and purified using liquid chromatography. Then, the mono- and co-infection models were treated by PQS in vitro and in vivo. RT-PCR analysis was used to look into changes in biofilm, QS, tissue regeneration, and apoptosis genes after the treatment.

RESULTS

PQS significantly disrupted established biofilm up to 90% in both in vitro and in vivo models. Moreover, a 93% reduction in the viability of S. aureus and P. aeruginosa was detected during the 10 days of treatment in comparison to control groups. In addition, the biofilm-encoding and QS-regulating genes were down-regulated to 75% in both microorganisms. Also, fewer epithelial cells died when treated with PQS compared to control groups in both mono- and co-infection groups.

CONCLUSION

According to this study, PQS may facilitate wound healing by stimulating the immune system and reducing apoptosis. It seems to be a potential medication to use in conjunction with antibiotics to treat infections that are difficult to treat.

Antimicrobial Activity of Two Different Types of Silver Nanoparticles against Wide Range of Pathogenic Bacteria

The emergence of antibiotic-resistant bacteria, particularly the most hazardous pathogens, namely Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, and Enterobacter spp. (ESKAPE)-pathogens pose a significant threat to global health. Current antimicrobial therapies, including those targeting biofilms, have shown limited effectiveness against these superbugs. Nanoparticles, specifically silver nanoparticles (AgNPs), have emerged as a promising alternative for combating bacterial infections. In this study, two types of AgNPs with different physic-chemical properties were evaluated for their antimicrobial and antibiofilm activities against clinical ESKAPE strains. Two types of silver nanoparticles were assessed: spherical silver nanoparticles (AgNPs-1) and cubic-shaped silver nanoparticles (AgNPs-2). AgNPs-2, characterized by a cubic shape and higher surface-area-to-volume ratio, exhibited superior antimicrobial activity compared to spherical AgNPs-1. Both types of AgNPs demonstrated the ability to inhibit biofilm formation and disrupt established biofilms, leading to membrane damage and reduced viability of the bacteria. These findings highlight the potential of AgNPs as effective antibacterial agents against ESKAPE pathogens, emphasizing the importance of nanoparticle characteristics in determining their antimicrobial properties. Further research is warranted to explore the underlying mechanisms and optimize nanoparticle-based therapies for the management of infections caused by antibiotic-resistant bacteria.

Membrane-enclosed Pseudomonas quinolone signal attenuates bacterial virulence by interfering with quorum sensing

Outer membrane vesicle (OMV)-delivered Pseudomonas quinolone signal (PQS) plays a critical role in cell-cell communication in Pseudomonas aeruginosa. However, the functions and mechanisms of membrane-enclosed PQS in interspecies communication in microbial communities are not clear. Here, we demonstrate that PQS delivered by both OMVs from P. aeruginosa and liposome reduces the competitiveness of Burkholderia cenocepacia, which usually shares the same niche in the lungs of cystic fibrosis patients, by interfering with quorum sensing (QS) in B. cenocepacia through the LysR-type regulator ShvR. Intriguingly, we found that ShvR regulates the production of the QS signals cis-2-dodecenoic acid (BDSF) and N-acyl homoserine lactone (AHL) by directly binding to the promoters of signal synthase-encoding genes. Perception of PQS influences the regulatory activity of ShvR and thus ultimately reduces QS signal production and virulence in B. cenocepacia. Our findings provide insights into the interspecies communication mediated by the membrane-enclosed QS signal among bacterial species residing in the same microbial community.IMPORTANCEQuorum sensing (QS) is a ubiquitous cell-to-cell communication mechanism. Previous studies showed that Burkholderia cenocepacia mainly employs cis-2-dodecenoic acid (BDSF) and N-acyl homoserine lactone (AHL) QS systems to regulate biological functions and virulence. Here, we demonstrate that Pseudomonas quinolone signal (PQS) delivered by outer membrane vesicles from Pseudomonas aeruginosa or liposome attenuates B. cenocepacia virulence by targeting the LysR-type regulator ShvR, which regulates the production of the QS signals BDSF and AHL in B. cenocepacia. Our results not only suggest the important roles of membrane-enclosed PQS in interspecies and interkingdom communications but also provide a new perspective on the use of functional nanocarriers loaded with QS inhibitors for treating pathogen infections.

Development of Quinazolinone Derivatives as Modulators of Virulence Factors of Pseudomonas aeruginosa Cystic Fibrosis Strains

Pseudomonas aeruginosa (PA), one of the ESKAPE pathogens, is an opportunistic Gram-negative bacterium responsible for nosocomial infections in humans but also for infections in patients affected by AIDS, cancer, or cystic fibrosis (CF). Treatment of PA infections in CF patients is a global healthcare problem due to the ability of PA to gain antibiotic tolerance through biofilm formation. Anti-virulence compounds represent a promising approach as adjuvant therapy, which could reduce or eliminate the pathogenicity of PA without impacting its growth. Pyocyanin is one of the virulence factors whose production is modulated by the Pseudomonas quinolone signal (PQS) through its receptor PqsR. Different PqsR modulators have been synthesized over the years, highlighting this new powerful therapeutic strategy. Based on the promising structure of quinazolin-4(3H)-one, we developed compounds 7a-d, 8a,b, 9, 10, and 11a-f able to reduce biofilm formation and the production of virulence factors (pyocyanin and pyoverdine) at 50 µM in two PA strains responsible for CF acute and chronic infections. The developed compounds did not reduce the cell viability of IB3-1 bronchial CF cells, and computational studies confirmed the potential ability of novel compounds to act as potential Pqs system modulators.

Screening and Identification of a Streptomyces Strain with Quorum-Sensing Inhibitory Activity and Effect of the Crude Extracts on Virulence Factors of Pseudomonas aeruginosa

Quorum-sensing (QS) is involved in numerous physiological processes in bacteria, such as biofilm formation, sporulation, and virulence formation. Therefore, the search for new quorum-sensing inhibitors (QSI) is a promising strategy that opens up a new perspective for controlling QS-mediated bacterial pathogens. To explore new QSIs, a strain named Streptomyces sp. D67 with QS inhibitory activity was isolated from the soil of the arid zone around the Kumutag Desert in Xinjiang. Phylogenetic analyses demonstrated that strain D67 shared the highest similarity with Streptomyces ardesiacus NBRC 15402T (98.39%), which indicated it represented a potential novel species in the Streptomyces genus. The fermentation crude extracts of strain D67 can effectively reduce the violacein production produced by Chromobacterium violaceum CV026 and the swarming and swimming abilities of Pseudomonas aeruginosa. It also has significant inhibitory activity on the production of virulence factors such as biofilm, pyocyanin, and rhamnolipids of P. aeruginosa in a significant concentration-dependent manner, but not on protease activity. A total of 618 compounds were identified from the fermentation crude extracts of strain D67 by LC-MS, and 19 compounds with significant QS inhibitory activity were observed. Overall, the strain with QS inhibitory activity was screened from Kumutag Desert in Xinjiang for the first time, which provided a basis for further research and development of new QSI.

Citrinin Is a Potential Quorum Sensing Inhibitor against Pseudomonas aeruginosa

Pseudomonas aeruginosa is an opportunistic pathogen that infects patients by regulating virulence factors and biofilms through a quorum sensing (QS) system to protect itself from antibiotics and environmental stress. Therefore, the development of quorum sensing inhibitors (QSIs) is expected to become a new strategy for studying drug resistance to P. aeruginosa infections. Marine fungi are valuable resources for screening QSIs. A marine fungus, Penicillium sp. JH1, with anti-QS activity was isolated from the offshore waters of Qingdao (China), and citrinin, a novel QSI, was purified from secondary metabolites of this fungus. Citrinin could significantly inhibit the production of violacein in Chromobacterium violaceum CV12472 and the production of three virulence factors (elastase, rhamnolipid and pyocyanin) in P. aeruginosa PAO1. It could also inhibit the biofilm formation and motility of PAO1. In addition, citrinin downregulated the transcript levels of nine genes (lasI, rhlI, pqsA, lasR, rhlR, pqsR, lasB, rhlA and phzH) associated with QS. Molecular docking results showed that citrinin bound to PqsR and LasR with better affinity than the natural ligands. This study laid a foundation for the further study of the structure optimization and structure-activity relationship of citrinin.

Pseudomonas aeruginosa behaviour in polymicrobial communities: The competitive and cooperative interactions conducting to the exacerbation of infections

Pseudomonas aeruginosa is mostly associated with persistent infections and antibiotic resistance as a result of several factors, biofilms one of them. Microorganisms within the polymicrobial biofilm (PMB) reveal various transcriptional profiles and affect each other which might influence their pathogenicity and antibiotic tolerance and subsequent worsening of the biofilm infection. P. aeruginosa within PMB exhibits various behaviours toward other microorganisms, which may enhance or repress the virulence of these microbes. Microbial neighbours, in turn, may affect P. aeruginosa's virulence either positively or negatively. Such interactions among microorganisms lead to emerging persistent and antibiotic-resistant infections. This review highlights the relationship between P. aeruginosa and its microbial neighbours within the PMB in an attempt to better understand the mechanisms of polymicrobial interaction and the correlation between increased exacerbations of infection and the P. aeruginosa-microbe interaction. Researching in the literature that was carried out in vitro either in co-cultures or in the models to simulate the environment at the site of infection suggested that the interplay between P. aeruginosa and other microorganisms is one main reason for the worsening of the infection and which in turn requires a treatment approach different from that followed with P. aeruginosa mono-infection.

Structural modification of the Pseudomonas aeruginosa alkylquinoline cell-cell communication signal, HHQ, leads to benzofuranoquinolines with anti-virulence behaviour in ESKAPE pathogens

Microbial populations have evolved intricate networks of negotiation and communication through which they can coexist in natural and host ecosystems. The nature of these systems can be complex and they are, for the most part, poorly understood at the polymicrobial level. The Pseudomonas Quinolone Signal (PQS) and its precursor 4-hydroxy-2-heptylquinoline (HHQ) are signal molecules produced by the important nosocomial pathogen Pseudomonas aeruginosa . They are known to modulate the behaviour of co-colonizing bacterial and fungal pathogens such as Bacillus atropheaus, Candida albicans and Aspergillus fumigatus. While the structural basis for alkyl-quinolone signalling within P. aeruginosa has been studied extensively, less is known about how structural derivatives of these molecules can influence multicellular behaviour and population-level decision-making in other co-colonizing organisms. In this study, we investigated a suite of small molecules derived initially from the HHQ framework, for anti-virulence activity against ESKAPE pathogens, at the species and strain levels. Somewhat surprisingly, with appropriate substitution, loss of the alkyl chain (present in HHQ and PQS) did not result in a loss of activity, presenting a more easily accessible synthetic framework for investigation. Virulence profiling uncovered significant levels of inter-strain variation among the responses of clinical and environmental isolates to small-molecule challenge. While several lead compounds were identified in this study, further work is needed to appreciate the extent of strain-level tolerance to small-molecule anti-infectives among pathogenic organisms.

Community composition shapes microbial-specific phenotypes in a cystic fibrosis polymicrobial model system

Interspecies interactions can drive the emergence of unexpected microbial phenotypes that are not observed when studying monocultures. The cystic fibrosis (CF) lung consists of a complex environment where microbes, living as polymicrobial biofilm-like communities, are associated with negative clinical outcomes for persons with CF (pwCF). However, the current lack of in vitro models integrating the microbial diversity observed in the CF airway hampers our understanding of why polymicrobial communities are recalcitrant to therapy in this disease. Here, integrating computational approaches informed by clinical data, we built a mixed community of clinical relevance to the CF lung composed of Pseudomonas aeruginosa, Staphylococcus aureus, Streptococcus sanguinis, and Prevotella melaninogenica. We developed and validated this model biofilm community with multiple isolates of these four genera. When challenged with tobramycin, a front-line antimicrobial used to treat pwCF, the microorganisms in the polymicrobial community show altered sensitivity to this antibiotic compared to monospecies biofilms. We observed that wild-type P. aeruginosa is sensitized to tobramycin in a mixed community versus monoculture, and this observation holds across a range of community relative abundances. We also report that LasR loss-of-function, a variant frequently detected in the CF airway, drives tolerance of P. aeruginosa to tobramycin specifically in the mixed community. Our data suggest that the molecular basis of this community-specific recalcitrance to tobramycin for the P. aeruginosa lasR mutant is increased production of phenazines. Our work supports the importance of studying a clinically relevant model of polymicrobial biofilms to understand community-specific traits relevant to infections.

Effect of Micro-Patterned Mucin on Quinolone and Rhamnolipid Profiles of Mucoid Pseudomonas aeruginosa under Antibiotic Stress

Pseudomonas aeruginosa (P. aeruginosa) is commonly implicated in hospital-acquired infections where its capacity to form biofilms on a variety of surfaces and the resulting enhanced antibiotic resistance seriously limit treatment choices. Because surface attachment sensitizes P. aeruginosa to quorum sensing (QS) and induces virulence through both chemical and mechanical cues, we investigate the effect of surface properties through spatially patterned mucin, combined with sub-inhibitory concentrations of tobramycin on QS and virulence factors in both mucoid and non-mucoid P. aeruginosa strains using multi-modal chemical imaging combining confocal Raman microscopy and matrix-assisted laser desorption/ionization-mass spectrometry. Samples comprise surface-adherent static biofilms at a solid-water interface, supernatant liquid, and pellicle biofilms at an air-water interface at various time points. Although the presence of a sub-inhibitory concentration of tobramycin in the supernatant retards growth and development of static biofilms independent of strain and surface mucin patterning, we observe clear differences in the behavior of mucoid and non-mucoid strains. Quinolone signals in a non-mucoid strain are induced earlier and are influenced by mucin surface patterning to a degree not exhibited in the mucoid strain. Additionally, phenazine virulence factors, such as pyocyanin, are observed in the pellicle biofilms of both mucoid and non-mucoid strains but are not detected in the static biofilms from either strain, highlighting the differences in stress response between pellicle and static biofilms. Differences between mucoid and non-mucoid strains are consistent with their strain-specific phenology, in which the mucoid strain develops highly protected biofilms.

Geraniol attenuates virulence factors by inhibiting quorum sensing of Pseudomonas aeruginosa

Pseudomonas aeruginosa is a ubiquitous opportunistic pathogen that can cause severe respiratory tract infections. Geraniol, a chemical component of essential oils, has antimicrobial and anti-inflammatory activities, along with low toxicity. However, the effect and mechanism of geraniol against P. aeruginosa virulence factors are rarely studied. In this study, we investigated the quorum sensing (QS) inhibitory effects and mechanisms of geraniol against P. aeruginosa PAO1, using physiological and biochemical techniques, quantitative reverse transcription polymerase chain reaction, and transcriptomics. Geraniol slightly affected P. aeruginosa PAO1 growth, prolonged the lag phase, and delayed growth periods in a concentration-dependent manner. Geraniol inhibited three QS systems of P. aeruginosa, las, rhl, and pqs by suppressing the expression level of their key genes, including the three signal synthetase encoding genes of lasI, rhlI, and pqsABCDEH, and the corresponding signal receptor encoding genes of lasR, rhlR, and pqsR. Geraniol also suppressed certain virulence genes regulated by these three QS systems, including rhlABC, lasAB, lecAB, phzABMS, and pelABG, resulting in the attenuation of the related virulence factors, rhamnolipids, exoprotease LasA, elastase, lectin, pyocyanin, and biofilm. In conclusion, geraniol can suppress the virulence factors of P. aeruginosa PAO1 by inhibiting the three QS systems of las, rhl, and pqs. This study is significant for improving the treatment of bacterial infections caused by P. aeruginosa.

Polymicrobial Infections and Biofilms: Clinical Significance and Eradication Strategies

Biofilms are population of cells growing in a coordinated manner and exhibiting resistance towards hostile environments. The infections associated with biofilms are difficult to control owing to the chronicity of infections and the emergence of antibiotic resistance. Most microbial infections are contributed by polymicrobial or mixed species interactions, such as those observed in chronic wound infections, otitis media, dental caries, and cystic fibrosis. This review focuses on the polymicrobial interactions among bacterial-bacterial, bacterial-fungal, and fungal-fungal aggregations based on in vitro and in vivo models and different therapeutic interventions available for polymicrobial biofilms. Deciphering the mechanisms of polymicrobial interactions and microbial diversity in chronic infections is very helpful in anti-microbial research. Together, we have discussed the role of metagenomic approaches in studying polymicrobial biofilms. The outstanding progress made in polymicrobial research, especially the model systems and application of metagenomics for detecting, preventing, and controlling infections, are reviewed.

The Molecular Architecture of Pseudomonas aeruginosa Quorum-Sensing Inhibitors

The survival selection pressure caused by antibiotic-mediated bactericidal and bacteriostatic activity is one of the important inducements for bacteria to develop drug resistance. Bacteria gain drug resistance through spontaneous mutation so as to achieve the goals of survival and reproduction. Quorum sensing (QS) is an intercellular communication system based on cell density that can regulate bacterial virulence and biofilm formation. The secretion of more than 30 virulence factors of P. aeruginosa is controlled by QS, and the formation and diffusion of biofilm is an important mechanism causing the multidrug resistance of P. aeruginosa, which is also closely related to the QS system. There are three main QS systems in P. aeruginosa: las system, rhl system, and pqs system. Quorum-sensing inhibitors (QSIs) can reduce the toxicity of bacteria without affecting the growth and enhance the sensitivity of bacterial biofilms to antibiotic treatment. These characteristics make QSIs a popular topic for research and development in the field of anti-infection. This paper reviews the research progress of the P. aeruginosa quorum-sensing system and QSIs, targeting three QS systems, which will provide help for the future research and development of novel quorum-sensing inhibitors.