The formation of biofilms by Pseudomonas aeruginosa: a review of the natural and synthetic compounds interfering with control mechanisms

Motility of Acinetobacter baumannii: regulatory systems and controlling strategies

Acinetobacter baumannii is a Gram-negative opportunistic zoonotic pathogenic bacterium that causes nosocomial infections ranging from minor to life-threatening. The clinical importance of this zoonotic pathogen is rapidly increasing due to the development of multiple resistance mechanisms and the synthesis of numerous virulence factors. Although no flagellum-mediated motility exists, it may move through twitching or surface-associated motility. Twitching motility is a coordinated multicellular movement caused by the extension, attachment, and retraction of type IV pili, which are involved in surface adherence and biofilm formation. Surface-associated motility is a kind of movement that does not need appendages and is most likely driven by the release of extra polymeric molecules. This kind of motility is linked to the production of 1,3-diaminopropane, lipooligosaccharide formation, natural competence, and efflux pump proteins. Since A. baumannii's virulence qualities are directly tied to motility, it is possible that its motility may be used as a specialized preventative or therapeutic measure. The current review detailed the signaling mechanism and involvement of various proteins in controlling A. baumannii motility. As a result, we have thoroughly addressed the role of natural and synthetic compounds that impede A. baumannii motility, as well as the underlying action mechanisms. Understanding the regulatory mechanisms behind A. baumannii's motility features will aid in the development of therapeutic drugs to control its infection. KEY POINTS: • Acinetobacter baumannii exhibits multiple resistance mechanisms. • A. baumannii can move owing to twitching and surface-associated motility. • Natural and synthetic compounds can attenuate A. baumannii motility.

Ser/Thr protein kinase Stk1 phosphorylates the key transcriptional regulator AlgR to modulate virulence and resistance in Pseudomonas aeruginosa

Pseudomonas aeruginosa is one of the leading causes of nosocomial infections worldwide and has emerged as a serious public health threat, due in large part to its multiple virulence factors and remarkable resistance capabilities. Stk1, a eukaryotic-type Ser/Thr protein kinase, has been shown in our previous work to be involved in the regulation of several signalling pathways and biological processes. Here, we demonstrate that deletion of stk1 leads to alterations in several virulence- and resistance-related physiological functions, including reduced pyocyanin and pyoverdine production, attenuated twitching motility, and enhanced biofilm production, extracellular polysaccharide secretion, and antibiotic resistance. Moreover, we identified AlgR, an important transcriptional regulator, as a substrate for Stk1, with its phosphorylation at the Ser143 site catalysed by Stk1. Intriguingly, both the deletion of stk1 and the mutation of Ser143 of AlgR to Ala result in similar changes in the above-mentioned physiological functions. Furthermore, assays of algR expression in these strains suggest that changes in the phosphorylation state of AlgR, rather than its expression level, underlie changes in these physiological functions. These findings uncover Stk1-mediated phosphorylation of AlgR as an important mechanism for regulating virulence and resistance in P. aeruginosa.

Acanthamoeba as a protective reservoir for Pseudomonas aeruginosa in a clinical environment

Pseudomonas aeruginosa is a growing concern in healthcare associated infections and poses significant risk to those with serious underlying health conditions. The antimicrobial resistance traits of the pathogen and ability to form biofilms make effective mitigation and disinfection strategies difficult. Added to this challenge is the role that free-living amoebae such as Acanthamoeba play in the detection, disinfection, and transmission of P. aeruginosa. P. aeruginosa can survive intracellularly within amoebae, which has the potential to limit detectability and permit transmission into high-risk areas. Herein, we have screened for the presence of Acanthamoeba species and P. aeruginosa within a functioning general hospital in Scotland using a culture and molecular approach, noting their presence at several sites over a 4-month period, particularly within floor drains connecting patient rooms. In addition, microbiome analysis revealed amoebae harbour a unique microbial community comprised primarily of Pseudomonas species that were not readily detected using microbiome sequencing techniques on environmental swabs. Having demonstrated that both organisms were consistently present in hospital settings, we investigated the relationship between Acanthamoeba and P. aeruginosa in the laboratory, showing that i) Acanthamoeba growth rate is increased in the presence of Pseudomonas biofilms and viable Pseudomonas persist within the amoebae and ii) hydrogen peroxide-based disinfectants are significantly less effective against an isolate of P. aeruginosa in the presence of Acanthamoeba than when the bacteria are incubated alone. These findings suggest that amoebae, and other protists, can influence the detection and persistence of P. aeruginosa in high-risk areas and should be considered when implementing mitigation strategies.

Dispersal of a dominant competitor can drive multispecies coexistence in biofilms

Despite competition for both space and nutrients, bacterial species often coexist within structured, surface-attached communities termed biofilms. While these communities play important, widespread roles in ecosystems and are agents of human infection, understanding how multiple bacterial species assemble to form these communities and what physical processes underpin the composition of multispecies biofilms remains an active area of research. Using a model three-species community composed of Pseudomonas aeruginosa, Escherichia coli, and Enterococcus faecalis, we show with cellular-scale resolution that biased dispersal of the dominant community member, P. aeruginosa, prevents competitive exclusion from occurring, leading to the coexistence of the three species. A P. aeruginosa bqsS deletion mutant no longer undergoes periodic mass dispersal, leading to the local competitive exclusion of E. coli. Introducing periodic, asymmetric dispersal behavior into minimal models, parameterized by only maximal growth rate and local density, supports the intuition that biased dispersal of an otherwise dominant competitor can permit coexistence generally. Colonization experiments show that WT P. aeruginosa is superior at colonizing new areas, in comparison to ΔbqsS P. aeruginosa, but at the cost of decreased local competitive ability against E. coli and E. faecalis. Overall, our experiments document how one species' modulation of a competition-dispersal-colonization trade-off can go on to influence the stability of multispecies coexistence in spatially structured ecosystems.

Mechanisms of action of berberine hydrochloride in planktonic cells and biofilms of Pseudomonas aeruginosa

The increasing prevalence of extensively drug-and pan-drug-resistant Pseudomonas aeruginosa is a major concern for global public health. Therefore, it is crucial to develop novel antimicrobials that specifically target P. aeruginosa and its biofilms. In the present study, we determined that berberine hydrochloride inhibited the growth of planktonic bacteria as well as prevented the formation of biofilms. Moreover, we observed downregulation in the expression of pslA and pelA biofilm-related genes. Compared with existing antibiotics, berberine hydrochloride exhibits multiple modes of action against P. aeruginosa. Our findings suggest that berberine hydrochloride exerts its antimicrobial effects by damaging bacterial cell membranes, generating reactive oxygen species (ROS), and reducing intracellular adenosine triphosphate (ATP) levels. Furthermore, berberine hydrochloride showed minimal cytotoxicity and reduced susceptibility to drug resistance. In a mouse model of peritonitis, it significantly inhibited the growth of P. aeruginosa and exhibited a strong bacteriostatic action. In conclusion, berberine hydrochloride is a safe and effective antibacterial agent that inhibits the growth of P. aeruginosa.

Isolation and Characterization of Potassium-Solubilizing Rhizobacteria (KSR) Promoting Cotton Growth in Saline-Sodic Regions

Cotton is highly sensitive to potassium, and Xinjiang, China's leading cotton-producing region, faces a severe challenge due to reduced soil potassium availability. Biofertilizers, particularly potassium-solubilizing rhizobacteria (KSR), convert insoluble potassium into plant-usable forms, offering a sustainable solution for evergreen agriculture. This study isolated and characterized KSR from cotton, elucidated their potassium solubilization mechanisms, and evaluated the effects of inoculating KSR strains on cotton seedlings. Twenty-three KSR strains were isolated from cotton rhizosphere soil using modified Aleksandrov medium. Their solubilizing capacities were assessed in a liquid medium. Strain A10 exhibited the highest potassium solubilization capacity (21.8 ppm) by secreting organic acids such as lactic, citric, acetic, and succinic acid, lowering the pH and facilitating potassium release. A growth curve analysis and potassium solubilization tests of A10 under alkali stress showed its vigorous growth and maintained solubilization ability at pH 8-9, with significant inhibition at pH 10. Furthermore, 16S rRNA sequencing identified strain A10 as Pseudomonas aeruginosa. Greenhouse pot experiments showed that inoculating cotton plants with strain A10 significantly increased plant height and promoted root growth. This inoculation also enhanced dry biomass accumulation in both the aerial parts and root systems of the plants, while reducing the root-shoot ratio. These results suggest that Pseudomonas aeruginosa A10 has potential as a biofertilizer, offering a new strategy for sustainable agriculture.

Cold Atmospheric Pressure Plasma Solutions for Sustainable Food Packaging

Increasing the number of resistant bacteria resistant to treatment is one of the leading causes of death worldwide. These bacteria are created in wounds and injuries and can be transferred through hospital equipment. Various attempts have been made to treat these bacteria in recent years, such as using different drugs and new sterilization methods. However, some bacteria resist drugs, and other traditional methods cannot destroy them. In the meantime, various studies have shown that cold atmospheric plasma can kill these bacteria through different mechanisms, making cold plasma a promising tool to deactivate bacteria. This new technology can be effectively used in the food industry because it has the potential to inactivate microorganisms such as spores and microbial toxins and increase the wettability and printability of polymers to pack fresh and dried food. It can also increase the shelf life of food without leaving any residue or chemical effluent. This paper investigates cold plasma's potential, advantages, and disadvantages in the food industry and sterilization.

Synergistic effects of inhaled aztreonam plus tobramycin on hypermutable cystic fibrosis Pseudomonas aeruginosa isolates in a dynamic biofilm model evaluated by mechanism-based modelling and whole genome sequencing

OBJECTIVE

Hypermutable Pseudomonas aeruginosa strains are highly prevalent in chronic lung infections of patients with cystic fibrosis (CF). Acute exacerbations of these infections have limited treatment options. This study aimed to investigate inhaled aztreonam and tobramycin against clinical hypermutable P. aeruginosa strains using the CDC dynamic in vitro biofilm reactor (CBR), mechanism-based mathematical modelling (MBM) and genomic studies.

METHODS

Two CF multidrug-resistant strains were investigated in a 168 h CBR (n = 2 biological replicates). Regimens were inhaled aztreonam (75 mg 8-hourly) and tobramycin (300 mg 12-hourly) in monotherapies and combination. The simulated pharmacokinetic profiles of aztreonam and tobramycin (t1/2 = 3 h) were based on published lung fluid concentrations in patients with CF. Total viable and resistant counts were determined for planktonic and biofilm bacteria. MBM of total and resistant bacterial counts and whole genome sequencing were completed.

RESULTS

Both isolates showed reproducible bacterial regrowth and resistance amplification for the monotherapies by 168 h. The combination performed synergistically, with minimal resistant subpopulations compared to the respective monotherapies at 168 h. Mechanistic synergy appropriately described the antibacterial effects of the combination regimen in the MBM. Genomic analysis of colonies recovered from monotherapy regimens indicated noncanonical resistance mechanisms were likely responsible for treatment failure.

CONCLUSION

The combination of aztreonam and tobramycin was required to suppress the regrowth and resistance of planktonic and biofilm bacteria in all biological replicates of both hypermutable multidrug-resistant P. aeruginosa CF isolates. The developed MBM could be utilised for future investigations of this promising inhaled combination.

Assessment of the catalytic and biological potential of yttrium and samarium-modified copper ferrite nanomaterials

The present study reports the preparation of crystalline and nanosized copper ferrite (CuFe2O4), Y3+ substituted CuFe2O4 (CuFe1.95Y0.05O4), and Sm3+ substituted CuFe2O4 (CuFe1.95Sm0.05O4) using a simple co-precipitation method. The XRD analysis confirmed the formation of the cubic spinel phase, while XPS studies validated the presence of Cu and Fe in 2+ and 3+ oxidation states respectively. Transmission electron microscopy (TEM) analysis revealed the nanoparticles with a diameter in the range of 10-60 nm. The introduction of fractional amounts of Y3+ and Sm3+ ions in the CuFe2O4 lattice enhanced the reduction of 4-nitrophenol, attributed to decreased particle size facilitating the reduction process. In the case of antimicrobial activity, Candida albican was found to be maximally sensitive to CuFe2O4 and CuFe1.95Y0.05O4, while Pseudomonas aeruginosa was inhibited by CuFe1.95Sm0.05O4. Moreover, a maximum of 61.9 ± 1.91 % anti-Pseudomonas biofilm activity and 75.7 ± 1.28 % DPPH radical scavenging activity was observed for CuFe1.95Y0.05O4 at 200 μg/ml concentration. The improvement in biological activities was attributed to the reduced particle size, crystal structure modification, and increased stability of the CuFe2O4 lattice with substitution. The enhancement in catalytic and biological performance highlighted the effectiveness of minimal Y3+ and Sm3+ concentrations in modulating the properties of CuFe2O4 nanomaterials.

Prevalence of Infections and Antimicrobial Resistance of ESKAPE Group Bacteria Isolated from Patients Admitted to the Intensive Care Unit of a County Emergency Hospital in Romania

The ESKAPE group (Enterococcus faecium, Staphylococcus aureus, Klebsiella Pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, Enterobacter spp.) is a group of bacteria very difficult to treat due to their high ability to acquire resistance to antibiotics and are the main cause of nosocomial infections worldwide, posing a threat to global public health. Nosocomial infections with MDR bacteria are found mainly in Intensive Care Units, due to the multitude of maneuvers and invasive medical devices used, the prolonged antibiotic treatments, the serious general condition of these critical patients, and the prolonged duration of hospitalization.

MATERIALS AND METHODS

During a period of one year, from January 2023 to December 2023, this cross-sectional study was conducted on patients diagnosed with sepsis admitted to the Intensive Care Unit of the Sibiu County Emergency Clinical Hospital. Samples taken were tracheal aspirate, catheter tip, pharyngeal exudate, wound secretion, urine culture, blood culture, and peritoneal fluid.

RESULTS

The most common bacteria isolated from patients admitted to our Intensive Care Unit was Klebsiella pneumoniae, followed by Acinetobacter baumanii and Pseudomonas aeruginosa. Gram-positive cocci (Enterococcus faecium and Staphilococcus aureus) were rarely isolated. Most of the bacteria isolated were MDR bacteria.

CONCLUSIONS

The rise of antibiotic and antimicrobial resistance among strains in the nosocomial environment and especially in Intensive Care Units raises serious concerns about limited treatment options.

Edible Medicinal Guava Fruit (Psidium guajava L.) Are a Source of Anti-Biofilm Compounds against Pseudomonas aeruginosa

Psidium guajava is one of the most common edible medicinal plants frequently used in Malagasy traditional medicine to treat gastrointestinal infections. In order to evaluate their probable antibacterial activities, three organic extracts (successive extractions by hexane, dichloromethane, and ethanol) of ripe guava fruits were assessed for their bactericidal and anti-virulence properties against P. aeruginosa PAO1. Although these three extracts have shown no direct antibacterial activity (MIC of 1000 µg/mL) and, at the non-bactericidal concentration of 100 µg/mL, no impact on the production of major P. aeruginosa PAO1 virulence factors (pyocyanin and rhamnolipids), the hexane and dichloromethane extracts showed significant anti-biofilm properties and the dichloromethane extract disrupted the P. aeruginosa PAO1 swarming motility. Bioguided fractionation of the dichloromethane extract led to the isolation and identification of lycopene and β-sitosterol-β-D-glucoside as major anti-biofilm compounds. Interestingly, both compounds disrupt P. aeruginosa PAO1 biofilm formation and maintenance with IC50 of 1383 µM and 131 µM, respectively. More interestingly, both compounds displayed a synergistic effect with tobramycin with a two-fold increase in its effectiveness in killing biofilm-encapsulated P. aeruginosa PAO1. The present study validates the traditional uses of this edible medicinal plant, indicating the therapeutic effectiveness of guava fruits plausibly through the presence of these tri- and tetraterpenoids, which deserve to be tested against pathogens generally implicated in diarrhea.

Eye infection risks from Pseudomonas aeruginosa via hand soap and eye drops

Eye infections from bacterial contamination of bulk-refillable liquid soap dispensers and artificial tear eye drops continue to occur, resulting in adverse health outcomes that include impaired vision or eye enucleation. Pseudomonas aeruginosa (P. aeruginosa), a common cause of eye infections, can grow in eye drop containers and refillable soap dispensers to high numbers. To assess the risk of eye infection, a quantitative microbial risk assessment for P. aeruginosa was conducted to predict the probability of an eye infection for two potential exposure scenarios: (i) individuals using bacteria-contaminated eye drops and (ii) contact lens wearers washing their hands with bacteria-contaminated liquid soap prior to placing the lens. The median risk of an eye infection using contaminated eye drops and hand soap for both single and multiple exposure events (per day) ranged from 10-1 to 10-4, with contaminated eye drops having the greater risk. The concentration of P. aeruginosa was identified as the parameter contributing the greatest variance on eye infection risk; therefore, the prevalence and level of bacterial contamination of the product would have the greatest influence on health risk. Using eye drops in a single-use container or with preservatives can mitigate bacterial growth, and using non-refillable soap dispensers is recommended to reduce contamination of hand soap. Given the opportunistic nature of P. aeruginosa and its ability to thrive in unique environments, additional safeguards to mitigate bacterial growth and exposure are warranted.IMPORTANCEPseudomonas aeruginosa (P. aeruginosa) is a pathogen that can persist in a variety of unusual environments and continues to pose a significant risk for public health. This quantitative microbial risk assessment (QMRA) estimates the potential human health risks, specifically for eye infections, associated with exposure to P. aeruginosa in bacteria-contaminated artificial tear eye drops and hand soap. This study applies the risk assessment framework of QMRA to evaluate eye infection risks through both consumer products. The study examines the prevalence of this pathogen in eye drops and soap, as well as the critical need to implement measures that will mitigate bacterial exposure (e.g., single-use soap dispensers and eye drops with preservatives). Additionally, limitations and challenges are discussed, including the need to incorporate data regarding consumer practices, which may improve exposure assessments and health risk estimates.

Synthesis and characterization of marine seagrass (Cymodocea serrulata) mediated titanium dioxide nanoparticles for antibacterial, antibiofilm and antioxidant properties

Cymodocea serrulata mediated titanium dioxide nanoparticles (TiO2 NPs) were successfully synthesized. The XRD pattern and FTIR spectra demonstrated the crystalline structure of TiO2 NPs and the presence of phenols, flavonoids and alkaloids in the extract. Further SEM revealed that TiO2 NPs has uniform structure and spherical in shape with their size ranged from 58 to 117 nm. Antibacterial activity of TiO2 NPs against methicillin-resistant Staphylococcus aureus (MRSA) and Vibrio cholerae (V. cholerae), provided the zone of inhibition of 33.9 ± 1.7 and 36.3 ± 1.9 mm, respectively at 100 μg/mL concentration. MIC of TiO2 NPs against MRSA and V. cholerae showed 84% and 87% inhibition at 180 μg/mL and 160 μg/mL respectively. Subsequently, the sub-MIC of V. cholerae demonstrated minimal or no impact on bacterial growth at concentration of 42.5 μg/mL concentration. In addition, TiO2 NPs exhibited their ability to inhibit the biofilm forming V. cholerae which caused distinct morphological and intercellular damages analysed using CLSM and TEM. The antioxidant properties of TiO2 NPs were demonstrated through TAA and DPPH assays and exposed its scavenging activity with IC50 value of 36.42 and 68.85 μg/mL which denotes its valuable antioxidant properties with potential health benefits. Importantly, the brine shrimp based lethality experiment yielded a low cytotoxic effect with 13% mortality at 100 μg/mL. In conclusion, the multifaceted attributes of C. serrulata mediated TiO2 NPs encompassed the antibacterial, antioxidant and anti-biofilm inhibition effects with low cytotoxicity in nature were highlighted in this study and proved the bioderived TiO2 NPs could be used as a promising agent for biomedical applications.

Unraveling the signaling roles of indole in an opportunistic pathogen Pseudomonas aeruginosa strain Jade-X

Pseudomonas aeruginosa, which can produce several toxins and form biofilm, is listed among the priority pathogens. Indole is a ubiquitous aromatic pollutant and signaling molecule produced by tryptophanase in bacteria. Herein, the impacts of indole on a newly isolated P. aeruginosa strain Jade-X were systematically investigated. Indole (0.5-2.0 mM) enhanced the biofilm production by 1.33-2.31-fold after 24 h incubation at 30 °C. However, the effects indole on biofilm formation were intricate and closely intertwined with factors such as incubation temperature, bacterial growth stage, and indole concentration. The twitching motility was enhanced by 1.15-1.99-fold by indole, potentially facilitating surface exploration and biofilm development. Indole reduced the production of virulence factors (pyocyanin and pyoverdine) as well as altered the surface properties (zeta potential and hydrophobicity). Transcriptional analysis revealed that indole (1.0 mM) significantly downregulated mexGHI-opmD efflux genes (4.73-6.91-fold) and virulence-related genes (pqs, pch, and pvd clusters, and flagella-related genes), while upregulating pili-related genes in strain Jade-X. The quorum sensing related signal regulators, including RhlR, LasR, and MvfR (PqsR), were not altered by indole, while other six transcriptional regulators (AmrZ, BfmR, PchR, QscR, SoxR, and SphR) were significantly affected, implying that indole effects might be regulated in a complex and delicate manner. This study should provide new insights into our understanding of indole signaling roles.

Anti-biofilm, drug delivery and cytotoxicity properties of dendrimers

Background and purpose

Treatments using antimicrobial agents have faced many difficulties as a result of biofilm formation by pathogenic microorganisms. The biofilm matrix formed by these microorganisms prevents antimicrobial agents from penetrating the interior where they can exact their activity effectively. Additionally, extracellular polymeric molecules associated with biofilm surfaces can absorb antimicrobial compounds, lowering their bioavailability. This problem has resulted in the quest for alternative treatment protocols, and the development of nanomaterials and devices through nanotechnology has recently been on the rise.

Research approach

The literature on dendrimers was searched for in databases such as Google Scholar, PubMed, and ScienceDirect.

Key results

As a nanomaterial, dendrimers have found useful applications as a drug delivery vehicle for antimicrobial agents against biofilm-mediated infections to circumvent these defense mechanisms. The distinctive properties of dendrimers, such as multi-valency, biocompatibility, high water solubility, non-immunogenicity, and biofilm matrix-/cell membrane fusogenicity (ability to merge with intracellular membrane or other proteins), significantly increase the efficacy of antimicrobial agents and reduce the likelihood of recurring infections.

Conclusion

This review outlines the current state of dendrimer carriers for biofilm treatments, provides examples of their real-world uses, and examines potential drawbacks.

Biofilm-Inhibitory Activity of Wild Mushroom Extracts against Pathogenic Bacteria

Objective

This study aims to investigate the bacterial biofilm-inhibitory effect of mushroom extracts.

Methods

Mushrooms were collected from Arabuko-Sokoke and Kakamega forests and identified using morphological and molecular approaches. Auricularia auricula-judae, Microporus xanthopus, Termitomyces umkowaani, Trametes elegans, and Trametes versicolor were extracted by chloroform, 70% ethanol, and hot water. Extracts were tested against Escherichia coli, Pseudomonas aeruginosa, and Staphylococcus aureus (ATCC25923). Data were analyzed using SPSS ver. 20.0.

Results

Chloroform, 70% ethanol, and hot water extracts of A. auricula-judae (50 μg/mL) showed statistically significant antibiofilm activities against P. aeruginosa, E. coli, and S. aureus (p ≤ 0.05). M. xanthopus extracts (250 μg/mL) revealed significantly significant antibiofilm activities against each test bacterium (p ≤ 0.05). All extracts of T. umkowaani (250 μg/mL) exhibited statistically significant antibiofilm activities against S. aureus only (p ≤ 0.05). Chloroform extract of T. elegans (250 μg/mL) showed the best antibiofilm activity (69.75 ± 0.01%) against S. aureus. All T. versicolor extracts (250 μg/mL) indicated the best antibiofilm activities against S. aureus.

Conclusions

Being the first study of its kind to be conducted in Kenya, it added a novel concept to the body of knowledge already known about medical biotechnology research. It offers a fresh understanding of the various varieties of mushrooms found in Kenya, their potential biological function in the production of drugs, particularly those that combat drug resistance, and perhaps even a peek at their bioactive elements. Wild mushrooms, a hidden gem, might help to reopen the pipeline of new antibiotics that have been on the decline. However, further research is required to determine the potential mechanism(s) of action of the extracts that are in charge of the apparent antibiofilm activity.

Ketoprofen attenuates Las/Rhl quorum-sensing (QS) systems of Pseudomonas aeruginosa: molecular and docking studies

BACKGROUND

Quorum sensing (QS) is the leading cause of persistent infections and recalcitrance to antibiotic treatment of Pseudomonas aeruginosa. Hence, QS inhibitors are promising agents for the potential treatment of P. aeruginosa infections.

METHODS AND RESULTS

Herein, the reducing effect of ketoprofen on virulence factors production including protease, hemolysin, pyocyanin, hydrogen cyanide, biofilm, and motility of P. aeruginosa strains was investigated. Furthermore, the quorum quenching activity of ketoprofen at the molecular level was examined by real-time PCR assessment. Our results showed that ketoprofen significantly attenuates virulence factors and biofilm formation in P. aeruginosa strains. Moreover, ketoprofen down-regulated the expression of lasI, lasR, rhlI, and rhlR genes, by 35-47, 22-48, 34-67, and 43-56%, respectively. As well, molecular docking simulation showed a high binding affinity of ketoprofen with QS regulatory proteins.

CONCLUSIONS

Consequently, this study confirmed the quorum quenching activity of ketoprofen, which could be employed as a useful agent for the treatment of P. aeruginosa infections.

Effect of conA-unbound proteins from Melipona beecheii honey on the formation of Pseudomonas aeruginosa ATCC 27853 biofilm

Pseudomonas aeruginosa is an opportunistic bacterium that can form a biofilm with the ability to colonize different surfaces and for increasing resistance to antibiotics. An alternative to solve this problem may be the use of non-glucose/mannose glycosylated proteins from Melipona beecheii honey, which are capable of inhibiting the growth of this pathogen. In this work, the antibiofilm activity of the conA-unbound protein fraction (F1) from M. beecheii was evaluated. The crude protein extract (CPE) and the F1 fraction inhibited the P. aeruginosa biofilm growth above 80% at 4 and 1.3 µg/mL, respectively. These proteins affected the structure of the biofilm, as well as fleQ and fleR gene expressions involved in the formation and regulation of the P. aeruginosa biofilm. The results demonstrated that the F1 fraction proteins of M. beecheii honey inhibit and affect the formation of the P. aeruginosa biofilm.

A review of chemical signaling pathways in the quorum sensing circuit of Pseudomonas aeruginosa

Pseudomonas aeruginosa, an increasingly common competitive and biofilm organism in healthcare infection with sophisticated, interlinked and hierarchic quorum systems (Las, Rhl, PQS, and IQS), creates the greatest threats to the medical industry and has rendered prevailing chemotherapy medications ineffective. The rise of multidrug resistance has evolved into a concerning and potentially fatal occurrence for human life. P. aeruginosa biofilm development is assisted by exopolysaccharides, extracellular DNA, proteins, macromolecules, cellular signaling and interaction. Quorum sensing is a communication process between cells that involves autonomous inducers and regulators. Quorum-induced infectious agent biofilms and the synthesis of virulence factors have increased disease transmission, medication resistance, infection episodes, hospitalizations and mortality. Hence, quorum sensing may be a potential therapeutical target for bacterial illness, and developing quorum inhibitors as an anti-virulent tool could be a promising treatment strategy for existing antibiotics. Quorum quenching is a prevalent technique for treating infections caused by microbes because it diminishes microbial pathogenesis and increases microbe biofilm sensitivity to antibiotics, making it a potential candidate for drug development. This paper examines P. aeruginosa quorum sensing, the hierarchy of quorum sensing mechanism, quorum sensing inhibition and quorum sensing inhibitory agents as a drug development strategy to supplement traditional antibiotic strategies.

Exploring Pseudomonas syringae pv. tomato biofilm-like aggregate formation in susceptible and PTI-responding Arabidopsis thaliana

Bacterial biofilm-like aggregates have been observed in plants, but their role in pathogenicity is underinvestigated. In the present study, we observed that extracellular DNA and polysaccharides colocalized with green fluorescent protein (GFP)-expressing Pseudomonas syringae pv. tomato (Pst) aggregates in Arabidopsis leaves, suggesting that Pst aggregates are biofilms. GFP-expressing Pst, Pst ΔalgU ΔmucAB (Pst algU mutant), and Pst ΔalgD ΔalgU ΔmucAB (Pst algU algD mutant) were examined to explore the roles of (1) alginate, a potential biofilm component; (2) Pst AlgU, thought to regulate alginate biosynthesis and some type III secretion system effector genes; and (3) intercellular salicylic acid (SA) accumulation during pathogen-associated molecular pattern-triggered immunity (PTI). Pst formed extensive aggregates in susceptible plants, whereas aggregate numbers and size were reduced in Pst algU and Pst algD algU mutants, and both multiplied poorly in planta, suggesting that aggregate formation contributes to Pst success in planta. However, in SA-deficient sid2-2 plants, Pst algD algU mutant multiplication and aggregate formation were partially restored, suggesting plant-produced SA contributes to suppression of Pst aggregate formation. Pst algD algU mutants formed fewer and smaller aggregates than Pst algU mutants, suggesting both AlgU and AlgD contribute to Pst aggregate formation. Col-0 plants accumulated low levels of SA in response to Pst and both mutants (Pst algU and Pst algD algU), suggesting the regulatory functions of AlgU are not involved in suppressing SA-mediated plant defence. Plant PTI was associated with highly reduced Pst aggregate formation and accumulation of intercellular SA in flg22-induced PTI-responding wild-type Col-0, but not in PTI-incompetent fls2, suggesting intercellular SA accumulation by Arabidopsis contributes to suppression of Pst biofilm-like aggregate formation during PTI.

Development and Regulation of the Extreme Biofilm Formation of Deinococcus radiodurans R1 under Extreme Environmental Conditions

To grow in various harsh environments, extremophiles have developed extraordinary strategies such as biofilm formation, which is an extremely complex and progressive process. However, the genetic elements and exact mechanisms underlying extreme biofilm formation remain enigmatic. Here, we characterized the biofilm-forming ability of Deinococcus radiodurans in vitro under extreme environmental conditions and found that extremely high concentrations of NaCl or sorbitol could induce biofilm formation. Meantime, the survival ability of biofilm cells was superior to that of planktonic cells in different extreme conditions, such as hydrogen peroxide stress, sorbitol stress, and high UV radiation. Transcriptome profiles of D. radiodurans in four different biofilm development stages further revealed that only 13 matched genes, which are involved in environmental information processing, carbohydrate metabolism, or stress responses, share sequence homology with genes related to the biofilm formation of Escherichia coli, Pseudomonas aeruginosa, and Staphylococcus aureus. Overall, 64% of the differentially expressed genes are functionally unknown, indicating the specificity of the regulatory network of D. radiodurans. The mutation of the drRRA gene encoding a response regulator strongly impaired biofilm formation ability, implying that DrRRA is an essential component of the biofilm formation of D. radiodurans. Furthermore, transcripts from both the wild type and the drRRA mutant were compared, showing that the expression of drBON1 (Deinococcus radioduransBON domain-containing protein 1) significantly decreased in the drRRA mutant during biofilm development. Further analysis revealed that the drBON1 mutant lacked the ability to form biofilm and DrRRA, and as a facilitator of biofilm formation, could directly stimulate the transcription of the biofilm-related gene drBON1. Overall, our work highlights a molecular mechanism mediated by the response regulator DrRRA for controlling extreme biofilm formation and thus provides guidance for future studies to investigate novel mechanisms that are used by D. radiodurans to adapt to extreme environments.

Identification and analysis of pathogenic bacteria causing outbreaks in Indian major carp aquaculture of Tripura

OBJECTIVE

The objective of this study was to investigate bacterial disease outbreaks in Indian major carp from aquaculture systems in Tripura, India, and identify the bacterial species associated with those outbreaks.

METHODS

A 3-year surveillance was conducted in eight districts of Tripura, during which nine bacterial disease outbreaks were recorded. Fourteen bacterial strains isolated from diseased Indian major carp were selected and identified using phenotypic, molecular (16S ribosomal RNA gene), and phylogenetic analyses. In vitro pathogenicity studies were performed to assess the potential pathogenicity of the isolated bacteria.

RESULT

The selected isolated strains were preliminarily identified under the genera Aeromonas (9 isolates), Acinetobacter (1 isolate), Citrobacter (3 isolates), and Pseudomonas (1 isolate). Molecular and phylogenetic analyses confirmed the species of the isolated bacteria, including Aeromonas jandaei (strains COF_AHE09 and COF_AHE61), Aeromonas veronii (strains COF_AHE13, COF_AHE52, COF_AHE55, COF_AHE56, and COF_AHE62), Aeromonas hydrophila (strains COF_AHE51 and COF_AHE58), Acinetobacter pittii (strain COF_AHE14), Citrobacter freundii (strains COF_AHE20, COF_AHE57, and COF_AHE59), and Pseudomonas aeruginosa (strain COF_AHE54). Behavioral and clinical signs observed in the diseased fish, such as lethargy, skin hemorrhaging, ulcers, fin and tail rot, exophthalmia, distended abdomen, scale loss, and skin discoloration, indicated the presence of bacterial septicemia. The in vitro pathogenicity studies highlighted the potential role of these bacteria in disease development, especially under environmental stress.

CONCLUSION

This study provides valuable insights into the diversity of bacterial species associated with bacterial disease outbreaks in Indian major carp from aquaculture systems in Tripura. It serves as the first comprehensive investigation of its kind, contributing to our understanding of bacterial infections in Indian major carp.

Furanone loaded aerogels are effective antibiofilm therapeutics in a model of chronic Pseudomonas aeruginosa wound infection

Almost 80% of chronic wounds have a bacterial biofilm present. These wound biofilms are caused by a range of organisms and are often polymicrobial. Pseudomonas aeruginosa is one of the most common causative organisms in wound infections and readily forms biofilms in wounds. To coordinate this, P. aeruginosa uses a process known as quorum sensing. Structural homologues of the quorum sensing signalling molecules have been used to disrupt this communication and prevent biofilm formation by Pseudomonas. However, these compounds have not yet reached clinical use. Here, we report the production and characterisation of a lyophilised PVA aerogel for use in delivering furanones to wound biofilms. PVA aerogels successfully release a model antimicrobial and two naturally occurring furanones in an aqueous environment. Furanone loaded aerogels inhibited biofilm formation in P. aeruginosa by up to 98.80%. Further, furanone loaded aerogels successfully reduced total biomass of preformed biofilms. Treatment with a sotolon loaded aerogel yielded a 5.16 log reduction in viable biofilm bound cells in a novel model of chronic wound biofilm, equivalent to the current wound therapy Aquacel AG. These results highlight the potential utility of aerogels in drug delivery to infected wounds and supports the use of biofilm inhibitory compounds as wound therapeutics.

Inhibition of biofilm formation, quorum sensing and virulence factor production in Pseudomonas aeruginosa PAO1 by selected LasR inhibitors

The quorum sensing network of Pseudomonas aeruginosa mediates the regulation of genes controlling biofilm formation and virulence factors. The rise of drug resistance to Pseudomonas aeruginosa infections has made quorum sensing-regulated biofilm formation in clinical settings a major issue. In the present study, LasR inhibitors identified in our previous study were evaluated for their antibiofilm and antiquorum sensing activities against P. aeruginosa PAO1. The compounds selected were (3-[2-(3,4-dimethoxyphenyl)-2-(1H-indol-3-yl)ethyl]-1-(2-fluorophenyl)urea) (C1), (3-(4-fluorophenyl)-2-[(3-methylquinoxalin-2-yl)methylsulfanyl]quinazolin-4-one) (C2) and (2-({4-[4-(2-methoxyphenyl)piperazin-1-yl]pyrimidin-2-yl}sulfanyl)-N-(2,4,6-trimethylphenyl)acetamide) (C3). The minimum inhibitory concentrations of C1 and C2 were 1000 μM, whereas that of C3 was 500 μM. At sub-MICs, the compounds showed potent antibiofilm activity without affecting the growth of P. aeruginosa PAO1. Electron microscopy confirmed the disruption of biofilm by the selected compounds. The antiquorum sensing activity of the compounds was revealed by the inhibition of violacein in Chromobacterium violaceum and the inhibition of swimming and swarming motilities in P. aeruginosa PAO1. Furthermore, the compounds also attenuated the production of quorum sensing-mediated virulence factors. The qRT-PCR revealed the downregulation of quorum sensing regulatory genes, namely lasI, lasR, rhlI, rhlR, lasB, pqsA and pqsR. The selected compounds also exhibited lower cytotoxicity against peripheral blood lymphocytes. Thus, this study could pave a way to explore these compounds for the development of therapeutic agent against Pseudomonas aeruginosa biofilm-related infections.

Relocating Glyceryl Trinitrate as an Anti-Virulence Agent against Pseudomonas aeruginosa and Serratia marcescens: Insights from Molecular and In Vivo Investigations

The problem of antibiotic resistance is a global critical public health concern. In light of the threat of returning to the pre-antibiotic era, new alternative approaches are required such as quorum-sensing (QS) disruption and virulence inhibition, both of which apply no discernible selective pressure on bacteria, therefore mitigating the potential for the development of resistant strains. Bearing in mind the significant role of QS in orchestrating bacterial virulence, disrupting QS becomes essential for effectively diminishing bacterial virulence. This study aimed to assess the potential use of sub-inhibitory concentration (0.25 mg/mL) of glyceryl trinitrate (GTN) to inhibit virulence in Serratia marcescens and Pseudomonas aeruginosa. GTN could decrease the expression of virulence genes in both tested bacteria in a significant manner. Histopathological study revealed the ability of GTN to alleviate the congestion in hepatic and renal tissues of infected mice and to reduce bacterial and leukocyte infiltration. This study recommends the use of topical GTN to treat topical infection caused by P. aeruginosa and S. marcescens in combination with antibiotics.

Design of β-Keto Esters with Antibacterial Activity: Synthesis, In Vitro Evaluation, and Theoretical Assessment of Their Reactivity and Quorum-Sensing Inhibition Capacity

This work proposes the design of β-keto esters as antibacterial compounds. The design was based on the structure of the autoinducer of bacterial quorum sensing, N-(3-oxo-hexanoyl)-l-homoserine lactone (3-oxo-C6-HSL). Eight β-keto ester analogues were synthesised with good yields and were spectroscopically characterised, showing that the compounds were only present in their β-keto ester tautomer form. We carried out a computational analysis of the reactivity and ADME (absorption, distribution, metabolism, and excretion) properties of the compounds as well as molecular docking and molecular dynamics calculations with the LasR and LuxS quorum-sensing (QS) proteins, which are involved in bacterial resistance to antibiotics. The results show that all the compounds exhibit reliable ADME properties and that only compound 7 can present electrophile toxicity. The theoretical reactivity study shows that compounds 6 and 8 present a differential local reactivity regarding the rest of the series. Compound 8 presents the most promising potential in terms of its ability to interact with the LasR and LuxS QS proteins efficiently according to its molecular docking and molecular dynamics calculations. An initial in vitro antimicrobial screening was performed against the human pathogenic bacteria Pseudomonas aeruginosa and Staphylococcus aureus as well as the phytopathogenic bacteria Pseudomonas syringae and Agrobacterium tumefaciens. Compounds 6 and 8 exhibit the most promising results in the in vitro antimicrobial screening against the panel of bacteria studied.

Age of Antibiotic Resistance in MDR/XDR Clinical Pathogen of Pseudomonas aeruginosa

Antibiotic resistance in Pseudomonas aeruginosa remains one of the most challenging phenomena of everyday medical science. The universal spread of high-risk clones of multidrug-resistant/extensively drug-resistant (MDR/XDR) clinical P. aeruginosa has become a public health threat. The P. aeruginosa bacteria exhibits remarkable genome plasticity that utilizes highly acquired and intrinsic resistance mechanisms to counter most antibiotic challenges. In addition, the adaptive antibiotic resistance of P. aeruginosa, including biofilm-mediated resistance and the formation of multidrug-tolerant persisted cells, are accountable for recalcitrance and relapse of infections. We highlighted the AMR mechanism considering the most common pathogen P. aeruginosa, its clinical impact, epidemiology, and save our souls (SOS)-mediated resistance. We further discussed the current therapeutic options against MDR/XDR P. aeruginosa infections, and described those treatment options in clinical practice. Finally, other therapeutic strategies, such as bacteriophage-based therapy and antimicrobial peptides, were described with clinical relevance.

Tetrandrine Derivatives as Promising Antibacterial Agents

This work reports on the antibacterial activity of two tetrandrine derivatives, with acridine (MAcT) and anthracene (MAnT) units, against Gram-positive and Gram-negative bacteria of clinical importance by the broth microdilution method as well as their antioxidant activity against ABTS•+ and DPPH•+ radicals. Unlike natural tetrandrine, its derivatives inhibited bacterial growth, showing selectivity against Staphylococcus aureus with notable activity of MAnT (MIC = 0.035 μg/mL); this compound also has good activity against the ABTS•+ radical (IC50 = 4.59 μg/mL). Cell membrane integrity studies and reactive oxygen species (ROS) detection by fluorescent stains helped to understand possible mechanisms related to antibacterial activity, while electrophoretic mobility assays showed that the derivatives can bind to bacterial DNA plasmid. The results indicate that MAnT can induce a general state of oxidative stress in S. aureus and Escherichia coli, while MAcT induces an oxidative response in S. aureus. Complementary electrochemical studies were included.

Imipenem and meropenem influence the Las/Rhl quorum-sensing systems in clinical isolates of Pseudomonas aeruginosa

The present study was conducted to study the influence of imipenem and meropenem at subinhibitory concentration on the transcriptional response of Las/Rhl quorum-sensing systems in isolates of Pseudomonas aeruginosa. In the present study, six representative carbapenem nonsusceptible clinical isolates of P. aeruginosa were obtained. The agar dilution method was used to determine the minimum inhibitory concentration against imipenem and meropenem. The bacterial isolates were then cultured up to the early log phase in fresh Luria Bertani (LB) broths at 37°C with and without 2 µg mL-1 imipenem and meropenem, respectively. mRNA was then isolated from the bacterial isolates and was immediately reverse-transcribed to cDNA. The relative quantity of the expression of the lasI, lasR, rhlI, and rhlR genes was assessed by quantitative real-time Polymerase Chain Reaction (PCR) using the ΔΔCt method. The transcriptional response of the lasI and lasR genes was upregulated at subinhibitory concentration of meropenem. In contrast, the transcriptional response of the lasI, lasR, and rhlR genes was downregulated at subinhibitory concentration of imipenem as compared to the expression in untreated isolates. The data obtained in the current study showcased the ability of imipenem and meropenem to influence the response of the quorum-sensing genes at subinhibitory concentration.

Biofilm modifiers: The disparity in paradigm of oral biofilm ecosystem

A biofilm is a population of sessile microorganisms that has a distinct organized structure and characteristics like channels and projections. Good oral hygiene and reduction in the prevalence of periodontal diseases arise from minimal biofilm accumulation in the mouth, however, studies focusing on modifying the ecology of oral biofilms have not yet been consistently effective. The self-produced matrix of extracellular polymeric substances and greater antibiotic resistance make it difficult to target and eliminate biofilm infections, which lead to serious clinical consequences that are often lethal. Therefore, a better understanding is required to target and modify the ecology of biofilms in order to eradicate the infection, not only in instances of oral disorders but also in terms of nosocomial infections. The review focuses on several biofilm ecology modifiers to prevent biofilm infections, as well as the involvement of biofilm in antibiotic resistance, implants or in-dwelling device contamination, dental caries, and other periodontal disorders. It also discusses recent advances in nanotechnology that may lead to novel strategies for preventing and treating infections caused by biofilms as well as a novel outlook to infection control.

Shift of human pathogen community composition and their potential human health risk after supply suspension in tap water

Water supply suspension-restoration can occur frequently due to the overhauling of civil infrastructure in developing countries and the shutdown of commercial buildings during the pandemic. For comprehensive insights into the effects of water supply suspension-restoration, this study characterized the variations of the pathogen community composition of the tap water and their infection risk under different water supply scenarios. Metagenomic sequencing revealed a significant change of the human pathogen profiles, among which the most dominant pathogen changed from Pseudomonas aeruginosa (4.91%) to Acinetobacter johnsonii (0.59%). Furthermore, absolute quantification of pathogens by propidium-monoazide-qPCR revealed that the abundance of the three typical pathogens (Pseudomonas aeruginosa, Mycobacterium avium and Salmonella sp.) showed an increase of 2.44 log to 3.60 log immediately after water supply suspension-restoration and did not return to the normal level even after 2-h supply restoration, except for Pseudomonas aeruginosa. Quantitative microbial risk assessment suggested the infection risks of the three pathogens arising from direct utilization of tap water under stable water supply, including dermal exposure and oral intake, were all above the threshold of 10^-4, and evidently increased after water supply suspension-restoration. This study warns us against the risk induced by the pathogens in tap water, especially after water supply suspension-restoration.

In vitro and in silico assessment of anti-quorum sensing activity of Naproxen against Pseudomonas aeruginosa

Serious infections caused by Pseudomonas aeruginosa are usually related to quorum sensing (QS)-dependent virulence factors. Hence, QS inhibition is a promising approach to overcoming P. aeruginosa infections. This study aimed to investigate the effect of naproxen on biofilm formation and QS-related virulence traits of P. aeruginosa. Furthermore, the anti-QS potential of naproxen was evaluated using real-time PCR and molecular docking analysis. Our findings supported the anti-QS activity of naproxen, as evidenced by down-regulation of the lasI and rhlI genes expression as well as the attenuation of bacterial protease, hemolysin, pyocyanin, biofilm, and motility. Additionally, the high binding affinity of naproxen with QS regulatory proteins was determined in the molecular docking simulation. Altogether, these findings suggest that naproxen has a promising potential in inhibiting QS-associated traits of P. aeruginosa.

A CcdB toxin-derived peptide acts as a broad-spectrum antibacterial therapeutic in infected mice

The bacterial toxin CcdB (Controller of Cell death or division B) targets DNA Gyrase, an essential bacterial topoisomerase, which is also the molecular target for fluoroquinolones. Here, we present a short cell-penetrating 24-mer peptide, CP1-WT, derived from the Gyrase-binding region of CcdB and examine its effect on growth of Escherichia coli, Salmonella Typhimurium, Staphylococcus aureus and a carbapenem- and tigecycline-resistant strain of Acinetobacter baumannii in both axenic cultures and mouse models of infection. The CP1-WT peptide shows significant improvement over ciprofloxacin in terms of its in vivo therapeutic efficacy in treating established infections of S. Typhimurium, S. aureus and A. baumannii. The molecular mechanism likely involves inhibition of Gyrase or Topoisomerase IV, depending on the strain used. The study validates the CcdB binding site on bacterial DNA Gyrase as a viable and alternative target to the fluoroquinolone binding site.

Selected rhizobacteria facilitated phytoremediation of barren and heavy metal contaminated gold mine tailings by Festuca arundinacea

Gold mine tailings pose a significant challenge for phytoremediation due to their poor nutrition and heavy metal pollution. Rhizobacteria-assisted phytoremediation is a promising method, yet limited research has been conducted on its application in gold mine tailings. In this study, rhizobacteria R1 (Bacillus paramycoides) and R2 (Klebsiella michiganensisW14T) were isolated from the rhizosphere of Festuca arundinacea (F. arundinacea) to enhance the phytoremediation of gold mine tailings. Our results showed that inoculation of R1 and R2 led to a significant increase in the average germination rates of F. arundinacea by 36.9% and 16.5%, respectively. Furthermore, the average plant height increased by 68.3% and 53.4%, respectively. Importantly, after inoculation with rhizobacteria, the contents of Mn, Pb, and As in F. arundinacea increased by 13.2-33.9%, 40.1-41.0%, and 98.1%-124.5%, respectively, indicating that the rhizobacteria enhanced the plant uptake of heavy metals. The improved nutrient content and enzyme activity in the tailings after inoculation with rhizobacteria were positively correlated with the heavy metal content in F. arundinacea. In addition, inoculation of rhizobacteria significantly altered the microbial community structure of the tailings, with Bacillus becoming the dominant genus in the rhizosphere tailings of F. arundinacea after R1 inoculation. Overall, our findings demonstrated that rhizobacteria R1 was better to enhance the phytoremediation of gold mine tailings. These results offer valuable insights into the mechanism of rhizobacteria-assisted phytoremediation and provide a practical method to enhance remediation of gold mine tailings.

The role of RNA regulators, quorum sensing and c-di-GMP in bacterial biofilm formation

Biofilms provide an ecological advantage against many environmental stressors, such as pH and temperature, making it the most common life-cycle stage for many bacteria. These protective characteristics make eradication of bacterial biofilms challenging. This is especially true in the health sector where biofilm formation on hospital or patient equipment, such as respirators, or catheters, can quickly become a source of anti-microbial resistant strains. Biofilms are complex structures encased in a self-produced polymeric matrix containing numerous components such as polysaccharides, proteins, signalling molecules, extracellular DNA and extracellular RNA. Biofilm formation is tightly controlled by several regulators, including quorum sensing (QS), cyclic diguanylate (c-di-GMP) and small non-coding RNAs (sRNAs). These three regulators in particular are fundamental in all stages of biofilm formation; in addition, their pathways overlap, and the significance of their role is strain-dependent. Currently, ribonucleases are also of interest for their potential role as biofilm regulators, and their relationships with QS, c-di-GMP and sRNAs have been investigated. This review article will focus on these four biofilm regulators (ribonucleases, QS, c-di-GMP and sRNAs) and the relationships between them.

Characterization of a soluble library of the Pseudomonas aeruginosa PAO1 membrane proteome with emphasis on c-di-GMP turnover enzymes

Studies of protein-protein interactions in membranes are very important to fully understand the biological function of a cell. The extraction of proteins from the native membrane environment is a critical step in the preparation of membrane proteins that might affect the stability of protein complexes. In this work, we used the amphiphilic diisobutylene/maleic acid copolymer to extract the membrane proteome of the opportunistic pathogen Pseudomonas aeruginosa, thereby creating a soluble membrane-protein library within a native-like lipid-bilayer environment. Size fractionation of nanodisc-embedded proteins and subsequent mass spectrometry enabled the identification of 3358 proteins. The native membrane-protein library showed a very good overall coverage compared to previous proteome data. The pattern of size fractionation indicated that protein complexes were preserved in the library. More than 20 previously described complexes, e.g. the SecYEG and Pili complexes, were identified and analyzed for coelution. Although the mass-spectrometric dataset alone did not reveal new protein complexes, combining pulldown assays with mass spectrometry was successful in identifying new protein interactions in the native membrane-protein library. Thus, we identified several candidate proteins for interactions with the membrane phosphodiesterase NbdA, a member of the c-di-GMP network. We confirmed the candidate proteins CzcR, PA4200, SadC, and PilB as novel interaction partners of NbdA using the bacterial adenylate cyclase two-hybrid assay. Taken together, this work demonstrates the usefulness of the native membrane-protein library of P. aeruginosa for the investigation of protein interactions and membrane-protein complexes. Data are available via ProteomeXchange with identifiers PXD039702 and PXD039700.

Antimicrobial Resistance: Two-Component Regulatory Systems and Multidrug Efflux Pumps

The number of multidrug-resistant bacteria is rapidly spreading worldwide. Among the various mechanisms determining resistance to antimicrobial agents, multidrug efflux pumps play a noteworthy role because they export extraneous and noxious substrates from the inside to the outside environment of the bacterial cell contributing to multidrug resistance (MDR) and, consequently, to the failure of anti-infective therapies. The expression of multidrug efflux pumps can be under the control of transcriptional regulators and two-component systems (TCS). TCS are a major mechanism by which microorganisms sense and reply to external and/or intramembrane stimuli by coordinating the expression of genes involved not only in pathogenic pathways but also in antibiotic resistance. In this review, we describe the influence of TCS on multidrug efflux pump expression and activity in some Gram-negative and Gram-positive bacteria. Taking into account the strict correlation between TCS and multidrug efflux pumps, the development of drugs targeting TCS, alone or together with already discovered efflux pump inhibitors, may represent a beneficial strategy to contribute to the fight against growing antibiotic resistance.

Genomic variability correlates with biofilm phenotypes in multidrug resistant clinical isolates of Pseudomonas aeruginosa

The multifactorial nature of Pseudomonas aeruginosa biofilm development and genomic variabilities implicates its resistance to conventional antimicrobials and virulence. Therefore, genetic determinants need to be extensively studied to block the early steps of biofilm or already formed biofilms. In this study, a total of 20 multidrug resistant (MDR) clinical P. aeruginosa isolates were evaluated for their biofilm forming abilities and related genes. Of the isolates tested, all of them showed surface attachment tendencies in nutrient limiting conditions, and classified as strong (SBF = 45%), moderate (MBF = 30%) and weak (WBF = 25%) biofilm formers. Complete genome sequencing of representative strong (DMC-27b), moderate (DMC-20c) and weak biofilm former (DMC-30b) isolates was performed. Analysis of biofilm related genes in the sequenced genomes revealed that, 80 of the 88 biofilm related genes possess 98-100% sequence identity to the reference PAO1 strain. Complete and partial sequence data of LecB proteins from tested isolates indicate that isolates containing PA14-like LecB sequences produced strong biofilms. All of the 7 pel operon protein coding genes in weak biofilm former isolate 30b showed significant nucleotide sequence variation with other tested isolates, and their corresponding proteins are 99% identical with the pel operon proteins of PA7. Bioinformatics analyses identified divergent sequence and structural features that separate PA7 like pel operon proteins from reference PAO1-like pel operon. Congo red and pellicle forming assays revealed that the sequence and structure variations may have interfered with the Pel production pathway and resulted in impaired Pel production in isolate 30b that has a PA7 like pel operon. Expression analysis also showed that both pelB and lecB genes were about 5 to 6 folds upregulated after 24 h in SBF 27b in comparison with WBF 30b. Our findings indicate significant genomic divergence in biofilm related genes of P. aeruginosa strains that affect their biofilm phenotypes.

Using staining as reference for spectral imaging: Its application for the development of an analytical method to predict the presence of bacterial biofilms

At present, although spectral imaging is known to have a great potential to provide a massive amount of valuable information, the lack of reference methods remains as one of the bottlenecks to access the full capacity of this technique. This work aims to present a staining-based reference method with digital image treatment for spectral imaging, in order to propose a fast, efficient, contactless and non-invasive analytical method to predict the presence of biofilms. Spectral images of Pseudomonasaeruginosa biofilms formed on high density polyethylene coupons were acquired in visible and near infrared (vis-NIR) range between 400 and 1000 nm. Crystal violet staining served as a biofilm indicator, allowing the bacterial cells and the extracellular matrix to be marked on the coupon. Treated digital images of the stained biofilms were used as a reference. The size and pixels of the hyperspectral and digital images were scaled and matched to each other. Intensity color thresholds were used to differentiate the pixels associate to areas containing biofilms from those ones placed in biofilm-free areas. The model facultative Gram-negative bacterium, P. aeruginosa, which can form highly irregularly shaped and heterogeneous biofilm structures, was used to enhance the strength of the method, due to its inherent difficulties. The results showed that the areas with high and low intensities were modeled with good performance, but the moderate intensity areas (with potentially weak or nascent biofilms) were quite challenging. Image processing and artificial neural networks (ANN) methods were performed to overcome the issues resulted from biofilm heterogeneity, as well as to train the spectral data for biofilm predictions.

Cellulose-Based Laser-Induced Graphene Devices for Electrochemical Monitoring of Bacterial Phenazine Production and Viability

As an easily disposable substrate with a microporous texture, paper is a well-suited, generic substrate to build analytical devices for studying bacteria. Using a multi-pass lasing process, cellulose-based laser-induced graphene (cLIG) with a sheet resistance of 43.7 ± 2.3 Ωsq-1 is developed and utilized in the fabrication of low-cost and environmentally-friendly paper sensor arrays. Two case studies with Pseudomonas aeruginosa and Escherichia coli demonstrate the practicality of the cLIG sensors for the electrochemical analysis of bacteria. The first study measures the time-dependent profile of phenazines released from both planktonic (up to 60 h) and on-chip-grown (up to 22 h) Pseudomonas aeruginosa cultures. While similarities do exist, marked differences in phenazine production are seen with cells grown directly on cLIG compared to the planktonic culture. Moreover, in planktonic cultures, pyocyanin levels increase early on and plateau around 20 h, while optical density measurements increase monotonically over the duration of testing. The second study monitors the viability and metabolic activity of Escherichia coli using a resazurin-based electrochemical assay. These results demonstrate the utility of cLIG paper sensors as an inexpensive and versatile platform for monitoring bacteria and could enable new opportunities in high-throughput antibiotic susceptibility testing, ecological studies, and biofilm studies.

Analysis of antiquorum-sensing and antibiofilm activity by pomelo peel extract (Citrus maxima) on multidrug-resistance Pseudomonas aeruginosa

Pseudomonas aeruginosa is gram-negative bacteria with high adaptability by forming biofilms and quorum-sensing mechanisms to avoid immune responses and antimicrobial agents which tend to develop into Multidrug Resistance (MDR) related to Healthcare-Associated Infection (HAI) with a prevalence of 3,8% in Indonesia and a mortality of up to 69%. Polyphenol compounds found in pomelo peels (Citrus maxima) have been shown to have antibiofilm and antiquorum-sensing effects but are less investigated. Therefore, this study aimed to investigate those effects on MDR P. aeruginosa. In vitro study design is performed to evaluate the inhibition effect of ethanolic extract on bacterial growth (Kirby-Bauer test), biofilm formation (biofilm assay), and quorum-sensing activity (pyocyanin and pyoverdine assay) on clinical isolates of MDR and ATCC strain as comparator. Furthermore, we employed computational methods using docking protein analysis. Biofilm formation was significantly inhibited by 71.1% ± 4.4% in MDR (pLasR and LasI) by active compounds of Citrus maxima. Molecular docking was used to further strengthen this hypothesis, showing no significant differences in bonding energy of polyphenol compounds found in pomelo peel with LasR and LasI compared to the native ligand and inhibitors. Pomelo peel extract can be considered as a potential therapy for MDR P. aeruginosa infection mediated based on its antibiofilm and antiquorum-sensing effects.

Micafungin effect on Pseudomonas aeruginosa metabolome, virulence and biofilm: potential quorum sensing inhibitor

The prevalence of antibiotic resistance in Pseudomonas aeruginosa places a heavy burden on the health care sectors urging the need to find alternative, non-antibiotic strategies. The interference with the P. aeruginosa quorum sensing (QS) system represents a promising alternative strategy to attenuate the bacterial virulency and its ability to form biofilms. Micafungin has been reported to impede the pseudomonal biofilm formation. However, the influences of micafungin on the biochemical composition and metabolites levels of P. aeruginosa have not been explored. In this study, the effect of micafungin (100 µg/mL) on the virulence factors, QS signal molecules and the metabolome of P. aeruginosa was studied using exofactor assay and mass spectrometry-based metabolomics approaches. Furthermore, confocal laser scanning microscopy (CLSM) using the fluorescent dyes ConA-FITC and SYPRO® Ruby was used to visualize micafungin disturbing effects on the pseudomonal glycocalyx and protein biofilm-constituents, respectively. Our findings showed that micafungin significantly decreased the production of various QS-controlled virulence factors (pyocyanin, pyoverdine, pyochelin and rhamnolipid), along with a dysregulation in the level of various metabolites involved in QS system, lysine degradation, tryptophan biosynthesis, TCA cycle, and biotin metabolism. In addition, the CLSM examination showed an altered matrix distribution. The presented findings highlight the promising role of micafungin as a potential quorum sensing inhibitor (QSI) and anti-biofilm agent to attenuate P. aeruginosa pathogenicity. In addition, they point to the promising role of metabolomics study in investigating the altered biochemical pathways in P. aeruginosa.

Evidence-Based Treatment of Pseudomonas aeruginosa Infections: A Critical Reappraisal

Multidrug-resistant (MDR)/extensively drug-resistant (XDR) Pseudomonas aeruginosa is emerging as a major threat related to adverse patient outcomes. The goal of this review is to describe evidence-based empiric and targeted treatment regimens that can be exploited when dealing with suspected or confirmed infections due to MDR/XDR P. aeruginosa. P. aeruginosa has inherent resistance to many drug classes, the capacity to form biofilms, and most importantly, the ability to quickly acquire resistance to ongoing treatments. Based on the presence of risk factors for MDR/XDR infections and local epidemiology, where large proportions of strains are resistant to classic beta-lactams, the recommended empirical treatment for suspected P. aeruginosa infections is based on ceftolozane-tazobactam or ceftazidime-avibactam. Where local epidemiology indicates low rates of MDR/XDR and there are no risk factors, a third or fourth generation cephalosporin can be used in the context of a "carbapenem-sparing" strategy. Whenever feasible, antibiotic de-escalation is recommended after antimicrobial susceptibility tests suggest that it is appropriate, and de-escalation is based on different resistance mechanisms. Cefiderocol and imipenem-cilastatin-relebactam withstand most resistance mechanisms and may remain active in cases with resistance to other new antibiotics. Confronting the growing threat of MDR/XDR P. aeruginosa, treatment choices should be wise, sparing newer antibiotics when dealing with a suspected/confirmed susceptible P. aeruginosa strain and choosing the right option for MDR/XDR P. aeruginosa based on specific types and resistance mechanisms.

Structurally diverse G-quadruplexes as the noncanonical nucleic acid drug target for live cell imaging and antibacterial study

The formation of G-quadruplex structures (G4s) in vitro from guanine (G)-rich nucleic acid sequences of DNA and RNA stabilized with monovalent cations, typically K⁺ and Na⁺, under physiological conditions, has been verified experimentally and some of them have high-resolution NMR or X-ray crystal structures; however, the biofunction of these special noncanonical secondary structures of nucleic acids has not been fully understood and their existence in vivo is still controversial at present. It is generally believed that the folding and unfolding of G4s in vivo is a transient process. Accumulating evidence has shown that G4s may play a role in the regulation of certain important cellular functions including telomere maintenance, replication, transcription and translation. Therefore, both DNA and RNA G4s of human cancer hallmark genes are recognized as the potential anticancer drug target for the investigation in cancer biology, chemical biology and drug discovery. The relationship between the sequence, structure and stability of G4s, the interaction of G4s with small molecules, and insights into the rational design of G4-selective binding ligands have been intensively studied over the decade. At present, some G4-ligands have achieved a new milestone and successfully entered the human clinical trials for anticancer therapy. Over the past few decades, numerous efforts have been devoted to anticancer therapy; however, G4s for molecular recognition and live cell imaging and for application as antibacterial agents and antibiofilms against antibiotic resistance have been obviously underexplored. The recent advances in G4-ligands in these areas are thus selected and discussed concentratedly in this article in order to shed light on the emerging role of G4s in chemical biology and therapeutic prospects against bacterial infections. In addition, the recently published molecular scaffolds for designing small ligands selectively targeting G4s in live cell imaging, bacterial biofilm imaging, and antibacterial studies are discussed. Furthermore, a number of underexplored G4-targets from the cytoplasmic membrane-associated DNA, the conserved promoter region of K. pneumoniae genomes, the RNA G4-sites in the transcriptome of E. coli and P. aeruginosa, and the mRNA G4-sites in the sequence for coding the vital bacterial FtsZ protein are highlighted to further explore in G4-drug development against human diseases.

Carbon/nitrogen ratios determine biofilm formation and characteristics in model microbial cultures

The influence of growth medium water chemistry, specifically carbon/nitrogen (C/N) molar ratios, on the characteristics and development of biofilms of the model microorganism Pseudomonas aeruginosa was investigated. C/N = 9 had a unique effect on biofilm composition as well as quorum sensing (QS) pathways, with higher concentrations of carbohydrates and proteins in the biofilm and a significant upregulation of the QS gene lasI in planktonic cells. The effect of C/N ratio on total attached biomass was negligible. Principal component analysis revealed a different behavior of most outputs such as carbohydrates and QS chemicals at C/N = 9, and pointed to correlations between parameters of biofilm formation and steady state distribution of cells and extracellular components. C/N ratio was also shown to influence organic compound utilization by both planktonic and sessile organisms, with a maximum chemical oxygen demand (COD) removal of 83% achieved by biofilms at C/N = 21. Planktonic cells achieved higher COD removal rates, but greater overall rates after six days occurred in biofilms. The development of a dual-species biofilm of P. aeruginosa and Nitrobacter winogradskyi was also influenced by C/N, with increase in the relative abundance of the slower-growing N. winogradskyi above C/N = 9. These results indicate that altering operational parameters related to C/N would be relevant for mitigating or promoting biofilm formation and function depending on the desired industrial application or treatment configuration.

Anti-Inflammatory, Anti-Bacterial, and Anti-Fungal Activity of Oligomeric Proanthocyanidins and Extracts Obtained from Lignocellulosic Agricultural Waste

It has now been proven that many pathogens that cause infections and inflammation gradually mutate and become resistant to antibiotics. Chemically synthesized drugs treating inflammation most often only affect symptoms, but side effects could lead to the failure of human organs' functionality. On the other hand, plant-derived natural compounds have a long-term healing effect. It was shown that sea buckthorn (SBT) twigs are a rich source of biologically active compounds, including oligomeric proanthocyanidins (PACs). This study aimed to assess the anti-pathogenic and anti-inflammatory activity of water/ethanol extracts and PACs obtained from the lignocellulosic biomass of eight SBT cultivars. The anti-pathogenic activity of extracts and PACs was studied against pathogenic bacteria Pseudomonas aeruginosa, Staphylococcus aureus, Escherichia coli, Bacillus cereus and fungus Candida albicans in 96-well plates by the two-fold serial broth microdilution method. The anti-bacterial activity of purified PACs was 4 and 10 times higher than for water and water/ethanol extracts, respectively, but the extracts had higher anti-fungal activity. Purified PACs showed the ability to reduce IL-8 and IL-6 secretion from poly-I:C-stimulated peripheral blood mononuclear cells. For the extracts and PACs of SBT cultivar 'Maria Bruvele' in the concentration range 0.0313-4.0 mg/mL, no toxic effect was observed.

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

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

Antimicrobial activity of water-soluble tetra-cationic porphyrins on Pseudomonas aeruginosa

This manuscript presents the cytotoxicity, antimicrobial activity, antibiofilm preliminary properties, and associated therapy with commercial drugs using water-soluble tetra-cationic porphyrins against Pseudomonas aeruginosa. Two commercial tetra-cationic porphyrins were tested against a standard strain of P. aeruginosa 01 (PA01) in antibacterial activity assays under dark conditions and irradiated with white light for 120 min. Porphyrin 4-H₂TMePor showed better antimicrobial activity and was chosen for further tests. Increased minimum inhibitory concentration was observed in the presence of reactive oxygen species, suggesting that photooxidation was mediated by the singlet oxygen production. In the time-kill curve assay, 4-H₂TMePor inhibited bacterial growth in 90 min of irradiation. The checkerboard assay revealed synergistic interactions. Biofilms of the standard PA01 strain and three clinical isolates were formed. The biofilm destruction assay was more efficient for PA01, significantly reducing the biofilm biomass formed compared to the positive control. The associated treatment to destroy the biofilm potentiated a significant decrease in the biofilm biomass compared to the positive control. The photosensitizer did not damage human keratinocytes or mouse fibroblasts in the cytotoxicity assays, demonstrating the safety of using 4-H₂TMePor. Atomic force microscopy indicated lower adhesion force, higher cell wall deformation, and higher dissipation energy in the treated control compared to untreated PA01. Given our findings, it is evident that water-soluble tetra-cationic porphyrins have excellent antimicrobial and a preliminary antibiofilm activity against Gram-negative bacteria, proving to be a potential photosensitizer for clinical use.

N-alkylimidazole derivatives as potential inhibitors of quorum sensing in Pseudomonas aeruginosa

Antimicrobial resistance is a threat to global public health. Microbial resistance is mediated by biofilm formation and virulence behavior during infection. Quorum sensing (QS), a cell-to-cell communication is frequently used by microbes to evade host immune systems. Inhibiting QS channels is a potential route to halt microbial activities and eliminate them. Imidazole has been shown to be a potent warhead in various antimicrobial agents. This study aims to evaluate alkyl-imidazole derivatives as potential inhibitors of QS and to explore the interactions of the compounds with LasR, a key protein in the QS machinery of Pseudomonas aeruginosa. The study revealed that imidazole derivatives with longer alkyl chains possessed better antimicrobial activities. Octylimidazole and decylimidazole emerged as compounds with better anti-virulence and biofilm inhibition properties while hexylimidazole showed the best inhibitory activity against Pseudomonas aeruginosa PAO1. The binding affinity of the compounds with LasR followed a similar trend as that observed in the QS inhibitory assays, suggesting that interaction with LasR may be important for QS inhibition.

A Review of Biofilm Formation of Staphylococcus aureus and Its Regulation Mechanism

Bacteria can form biofilms in natural and clinical environments on both biotic and abiotic surfaces. The bacterial aggregates embedded in biofilms are formed by their own produced extracellular matrix. Staphylococcus aureus (S. aureus) is one of the most common pathogens of biofilm infections. The formation of biofilm can protect bacteria from being attacked by the host immune system and antibiotics and thus bacteria can be persistent against external challenges. Therefore, clinical treatments for biofilm infections are currently encountering difficulty. To address this critical challenge, a new and effective treatment method needs to be developed. A comprehensive understanding of bacterial biofilm formation and regulation mechanisms may provide meaningful insights against antibiotic resistance due to bacterial biofilms. In this review, we discuss an overview of S. aureus biofilms including the formation process, structural and functional properties of biofilm matrix, and the mechanism regulating biofilm formation.