Pseudomonas aeruginosa biofilms: role of the alginate exopolysaccharide

Antimicrobial resistance and carbapenemase dissemination in Pseudomonas aeruginosa isolates from Libyan hospitals: a call for surveillance and intervention

Pseudomonas aeruginosa is a multidrug-resistant bacterium capable of forming biofilms. This study aimed to assess resistance of clinical isolates from Libyan hospitals to antipseudomonal antibiotics, the prevalence of selected extended-spectrum β-lactamases and carbapenemase genes among these isolates, and the microorganisms' capacity for alginate and biofilm production. Forty-five isolates were collected from four hospitals in Benghazi and Derna, Libya. Antimicrobial susceptibility was determined using agar disc diffusion. The presence of resistance genes (blaCTXM, blaTEM, blaSHV-1, blaGES-1, blaKPC, and blaNDM) was screened using PCR. Biofilm formation was quantified via the crystal violet assay, while alginate production was measured spectrophotometrically. Resistance to antipseudomonal antibiotics ranged from 48.9% to 75.6%. The most prevalent resistance gene was blaNDM (26.7%), followed by blaGES-1 (17.8%). Moreover, all isolates demonstrated varying degrees of biofilm-forming ability and alginate production. No statistically significant correlation was found between biofilm formation and alginate production. The dissemination of resistant genes in P. aeruginosa, particularly carbapenemases, is of great concern. This issue is compounded by the bacteria's biofilm-forming capability. Urgent intervention and continuous surveillance are imperative to prevent further deterioration and the catastrophic spread of resistance among these formidable bacteria.

Customized Lanthanide Nanobiohybrids for Noninvasive Precise Phototheranostics of Pulmonary Biofilm Infection

A noninvasive strategy for in situ diagnosis and precise treatment of bacterial biofilm infections is highly anticipated but still a great challenge. Currently, no in vivo biofilm-targeted theranostic agent is available. Herein, we fabricated intelligent theranostic alginate lyase (Aly)-NaNdF4 nanohybrids with a 220 nm sunflower-like structure (NaNdF4@DMS-Aly) through an enrichment-encapsulating strategy, which exhibited excellent photothermal conversion efficiency and the second near-infrared (NIR-II) luminescence. Benefiting from the site-specific targeting and biofilm-responsive Aly release from NaNdF4@DMS-Aly, we not only enabled noninvasive diagnosis but also realized Aly-photothermal synergistic therapy and real-time evaluation of therapeutic effect in mice models with Pseudomonas aeruginosa biofilm-induced pulmonary infection. Furthermore, such nanobiohybrids with a sheddable siliceous shell are capable of delaying the NaNdF4 dissolution and biodegradation upon accomplishing the therapy, which is highly beneficial for the biosafety of theranostic agents.

Antimicrobial resistance of Pseudomonas aeruginosa: navigating clinical impacts, current resistance trends, and innovations in breaking therapies

Pseudomonas aeruginosa, a Gram-negative bacterium, is recognized for its adaptability and opportunistic nature. It poses a substantial challenge in clinical settings due to its complicated antibiotic resistance mechanisms, biofilm formation, and capacity for persistent infections in both animal and human hosts. Recent studies revealed a potential zoonotic transmission of P. aeruginosa between animals, the environment, and human populations which highlights awareness of this microbe. Implementation of the One Health approach, which underscores the connection between human, animal, and environmental health, we aim to offer a comprehensive perspective on the current landscape of P. aeruginosa management. This review presents innovative strategies designed to counteract P. aeruginosa infections. Traditional antibiotics, while effective in many cases, are increasingly compromised by the development of multidrug-resistant strains. Non-antibiotic avenues, such as quorum sensing inhibition, phage therapy, and nanoparticle-based treatments, are emerging as promising alternatives. However, their clinical application encounters obstacles like cost, side effects, and safety concerns. Effectively addressing P. aeruginosa infections necessitates persistent research efforts, advancements in clinical development, and a comprehension of host-pathogen interactions to deal with this resilient pathogen.

Evaluating disinfectant efficacy on mixed biofilms comprising Shiga toxigenic Escherichia coli, lactic acid bacteria, and spoilage microorganisms

This study aimed to investigate the impact of temperature and the presence of other microorganisms on the susceptibility of STEC to biocides. Mature biofilms were formed at both 10°C and 25°C. An inoculum of planktonic bacteria comprising 106 CFU/mL of spoilage bacteria and 103 CFU/mL of a single E. coli strain (O157, O111, O103, and O12) was used to form mixed biofilms. The following bacterial combinations were tested: T1: Carnobacterium piscicola + Lactobacillus bulgaricus + STEC, T2: Comamonas koreensis + Raoultella terrigena + STEC, and T3: Pseudomonas aeruginosa + C. koreensis + STEC. Tested biocides included quaternary ammonium compounds (Quats), sodium hypochlorite (Shypo), sodium hydroxide (SHyd), hydrogen peroxide (HyP), and BioDestroy®-organic peroxyacetic acid (PAA). Biocides were applied to 6-day-old biofilms. Minimum Bactericidal Concentrations (MBC) and Biofilm Eradication Concentrations (BEC) were determined. Planktonic cells and single-species biofilms exhibited greater susceptibility to sanitizers (p < 0.0001). Lactobacillus and Carnobacterium were more susceptible than the rest of the tested bacteria (p < 0.0001). Single species biofilms formed by E. coli O111, O121, O157, and O45 showed resistance (100%) to Shypo sanitizer (200 ppm) at 25°C. From the most effective to the least effective, sanitizer performance on single-species biofilms was PAA > Quats > HyP > SHyd > Shypo. In multi-species biofilms, spoilage bacteria within T1, T2, and T3 biofilms showed elevated resistance to SHyd (30%), followed by quats (23.25%), HyP (15.41%), SHypo (9.70%), and BioDestroy® (3.42%; p < 0.0001). Within T1, T2, and T3, the combined STEC strains exhibited superior survival to Quats (23.91%), followed by HyP (19.57%), SHypo (18.12%), SHyd (16.67%), and BioDestroy® (4.35%; p < 0.0001). O157:H7-R508 strains were less tolerant to Quats and Shypo when combined with T2 and T3 (p < 0.0001). O157:H7 and O103:H2 strains in mixed biofilms T1, T2, and T3 exhibited higher biocide resistance than the weak biofilm former, O145:H2 (p < 0.0001). The study shows that STEC within multi-species biofilms' are more tolerant to disinfectants.

Volatile methyl jasmonate from roots triggers host-beneficial soil microbiome biofilms

The rhizosphere is a niche surrounding plant roots, where soluble and volatile molecules mediate signaling between plants and the associated microbiota. The preferred lifestyle of soil microorganisms is in the form of biofilms. However, less is known about whether root volatile organic compounds (rVOCs) can influence soil biofilms beyond the 2-10 mm rhizosphere zone influenced by root exudates. We report that rVOCs shift the microbiome composition and growth dynamics of complex soil biofilms. This signaling is evolutionarily conserved from ferns to higher plants. Methyl jasmonate (MeJA) is a bioactive signal of rVOCs that rapidly triggers both biofilm and microbiome changes. In contrast to the planktonic community, the resulting biofilm community provides ecological benefits to the host from a distance via growth enhancement. Thus, a volatile host defense signal, MeJA, is co-opted for assembling host-beneficial biofilms in the soil microbiota and extending the sphere of host influence in the rhizosphere.

Comprehensive genome analysis of Pseudomonas sp. SWRIQ11, a new plant growth-promoting bacterium that alleviates salinity stress in olive

The study presents the genome analysis of a new Pseudomonas sp. (SWRIQ11), which can alleviate salinity stress effects on growth of olive seedlings in greenhouse study. The strain SWRIQ11 can tolerate salinity up to 6%, produce siderophores, indole acetic acid (IAA), aminocyclopropane-1-carboxylate (ACC) deaminase, and has the phosphate-solubilizing capability. The SWRIQ11 genome contained an assembly size of 6,196,390 bp with a GC content of 60.1%. According to derived indices based on whole-genome sequences for species delineation, including tetra nucleotide usage patterns (TETRA), genome-to-genome distance (GGDC), and average nucleotide identity (ANI), Pseudomonas sp. SWRIQ11 can be considered a novel species candidate. The phylogenetic analysis revealed SWRIQ11 clusters with Pseudomonas tehranensis SWRI196 in the same clade. The SWRIQ11 genome was rich in genes related to stress sensing, signaling, and response, chaperones, motility, attachments, colonization, and enzymes for degrading plant-derived carbohydrates. Furthermore, the genes for production of exopolysaccharides, osmoprotectants, phytohormones, and ACC deaminase, ion homeostasis, nutrient acquisition, and antioxidant defenses were identified in the SWRIQ11 genome. The results of genome analysis (identification of more than 825 CDSs related to plant growth-promoting and stress-alleviating traits in the SWRIQ11 genome which is more than 15% of its total CDSs) are in accordance with laboratory and greenhouse experiments assigning the Pseudomonas sp. SWRIQ11 as a halotolerant plant growth-promoting bacterium (PGPB). This research highlights the potential safe application of this new PGPB species in agriculture as a potent biofertilizer.

Extracellular DNA enhances biofilm integrity and mechanical properties of mucoid Pseudomonas aeruginosa

Pseudomonas aeruginosa is one of the most common biofilm-forming pathogens responsible for lung infections of individuals with cystic fibrosis (CF). P. aeruginosa becomes tolerant to antimicrobials in the biofilm state and is difficult to treat. Production of extracellular polymeric substances (EPS), such as alginate and extracellular DNA (eDNA), can allow adherence to abiotic and biotic surfaces, antimicrobial evasion, and resilience to environmental pressures. Alginate-producing mucoid variants of P. aeruginosa are frequently isolated from CF airway samples and are associated with worsening patient outcomes. While eDNA is a major structural component of nonmucoid P. aeruginosa biofilms, the potential role of eDNA in mucoid biofilms is unclear. Here, we investigate how eDNA contributes to clinical mucoid biofilm physiology and integrity. We predicted that eDNA plays a structural and mechanical role in mucoid biofilms. To test this, we quantified biofilm eDNA in mucoid biofilms and used microscopy and rheology to visualize eDNA and detect changes in biofilm structure and mechanics upon DNaseI treatment. We showed that biofilm eDNA abundance is diverse across clinical mucoid strains and observed a temporal increase in foci of eDNA within intact mucoid biofilms. Increased cell dispersal and reduced biomass were also observed following DNaseI treatment of mucoid biofilms. Degradation of eDNA also impacted the mechanical integrity of mucoid biofilms by increasing the stiffness and decreasing the cohesion of the biofilm. These findings advance our understanding of clinical mucoid P. aeruginosa biofilms and facilitate the development of new approaches to target biofilms by exploiting the functions of EPS components. IMPORTANCE Understanding the role of eDNA in mucoid Pseudomonas aeruginosa biofilms will lead to therapeutic strategies that combat the biophysical and structural function of EPS for the eradication of bacteria in mucoid biofilms during chronic infections. This knowledge can be used to further identify unknown matrix component interactions within pathogenic biofilm-forming clinical isolates.

Pleiotropic hubs drive bacterial surface competition through parallel changes in colony composition and expansion

Bacteria commonly adhere to surfaces where they compete for both space and resources. Despite the importance of surface growth, it remains largely elusive how bacteria evolve on surfaces. We previously performed an evolution experiment where we evolved distinct Bacilli populations under a selective regime that favored colony spreading. In just a few weeks, colonies of Bacillus subtilis showed strongly advanced expansion rates, increasing their radius 2.5-fold relative to that of the ancestor. Here, we investigate what drives their rapid evolution by performing a uniquely detailed analysis of the evolutionary changes in colony development. We find mutations in diverse global regulators, RicT, RNAse Y, and LexA, with strikingly similar pleiotropic effects: They lower the rate of sporulation and simultaneously facilitate colony expansion by either reducing extracellular polysaccharide production or by promoting filamentous growth. Combining both high-throughput flow cytometry and gene expression profiling, we show that regulatory mutations lead to highly reproducible and parallel changes in global gene expression, affecting approximately 45% of all genes. This parallelism results from the coordinated manner by which regulators change activity both during colony development-in the transition from vegetative growth to dormancy-and over evolutionary time. This coordinated activity can however also break down, leading to evolutionary divergence. Altogether, we show how global regulators function as major pleiotropic hubs that drive rapid surface adaptation by mediating parallel changes in both colony composition and expansion, thereby massively reshaping gene expression.

Biological macromolecules-based nanoformulation in improving wound healing and bacterial biofilm-associated infection: A review

A chronic wound is a serious complication associated with diabetes mellitus and is difficult to heal due to high glucose levels, oxidative stress, and biofilm-associated microbial infection. The structural complexity of microbial biofilm makes it impossible for antibiotics to penetrate the matrix, hence conventional antibiotic therapies became ineffective in clinical settings. This demonstrates an urgent need to find safer alternatives to reduce the prevalence of chronic wound infection associated with microbial biofilm. A novel approach to address these concerns is to inhibit biofilm formation using biological-macromolecule based nano-delivery system. Higher drug loading efficiency, sustained drug release, enhanced drug stability, and improved bioavailability are advantages of employing nano-drug delivery systems to prevent microbial colonization and biofilm formation in chronic wounds. This review covers the pathogenesis, microbial biofilm formation, and immune response to chronic wounds. Furthermore, we also focus on macromolecule-based nanoparticles as wound healing therapies to reduce the increased mortality associated with chronic wound infections.

A Mildly Acidic Environment Alters Pseudomonas aeruginosa Virulence and Causes Remodeling of the Bacterial Surface

Pseudomonas aeruginosa is a versatile pathogen that resists environmental stress, such as suboptimal pH. As a result of exposure to environmental stress, P. aeruginosa shows an altered virulence-related phenotype. This study investigated the modifications that P. aeruginosa undertakes at a mildly low pH (pH 5.0) compared with the bacteria grown in a neutral medium (pH 7.2). Results indicated that in a mildly acidic environment, expression of two-component system genes (phoP/phoQ and pmrA/pmrB), lipid A remodeling genes such as arnT and pagP and virulence genes, i.e., pqsE and rhlA, were induced. Moreover, lipid A of the bacteria grown at a mildly low pH is modified by adding 4-amino-arabinose (l-Ara4N). Additionally, the production of virulence factors such as rhamnolipid, alginate, and membrane vesicles is significantly higher in a mildly low-pH environment than in a neutral medium. Interestingly, at a mildly low pH, P. aeruginosa produces a thicker biofilm with higher biofilm biomass. Furthermore, studies on inner membrane viscosity and permeability showed that a mildly low pH causes a decrease in the inner membrane permeability and increases its viscosity. Besides, despite the importance of PhoP, PhoQ, PmrA, and PmrB in Gram-negative bacteria for responding to low pH stress, we observed that the absence of each of these two-component systems does not meaningfully impact the remodeling of the P. aeruginosa envelope. Given that P. aeruginosa is likely to encounter mildly acidic environments during infection in its host, the alterations that the bacterium undertakes under such conditions must be considered in designing antibacterial strategies against P. aeruginosa. IMPORTANCE P. aeruginosa encounters environments with acidic pH when establishing infections in hosts. The bacterium develops an altered phenotype to tolerate a moderate decrease in the environmental pH. At the level of the bacterial envelope, modified lipid A composition and a reduction of the bacterial inner membrane permeability and fluidity are among the changes P. aeruginosa undergoes at a mildly low pH. Also, the bacterium is more likely to form biofilm in a mildly acidic environment. Overall, these alterations in the P. aeruginosa phenotype put obstacles in the way of antibacterial activities. Thus, considering physiological changes in the bacterium at low pH helps design and implement antimicrobial approaches against this hostile microorganism.

Sonophotodynamic inactivation of Pseudomonas aeruginosa biofilm mediated by curcumin

The inactivation of Pseudomonas aeruginosa biofilm is a major challenge, as biofilms are less responsive to conventional treatments and responsible for persistent infections. This has led to the investigation of alternative approaches for biofilm control such as photodynamic (PDI) and sonodynamic (SDI) inactivation. The combination of them, known as Sonophotodynamic Inactivation (SPDI), has improved the effectiveness of the process. Curcumin, a well-established photosensitizer, has been identified as a potential sonosensitizer. This study evaluated the most effective combination for SPDI against P. aeruginosa biofilms in vitro, varying curcumin concentrations and ultrasound intensities. The results indicated that the inactivation was directly proportional to the curcumin concentration. Using curcumin 120 µM and 3.0 W.cm-2 of ultrasound intensity, SPDI demonstrated the highest and the best synergistic results, equivalent to 6.9 ± 2.1 logs of reduction. PDI reduced 0.7 ± 0.9 log and SDI had no effect. In conclusion, SPDI with curcumin is a promising approach for biofilm inactivation.

Antimicrobial Activity and Cytotoxicity of Prepolymer Allyl 2-cyanoacrylate and 2-Octyl Cyanoacrylate Mixture Adhesives for Topical Wound Closure

The development of a new skin adhesive that can be used inside and outside the body, which prevents infection and has fewer scars and less side effects, is currently attracting attention from the scientific community. To improve biocompatibility, prepolymer allyl 2-cyanoacrylate (PAC) and 2-octyl cyanoacrylate (OC) were mixed in various proportions and tested for their therapeutic potential as skin adhesives. A series of skin adhesive samples prepared by mixing PAC, OC, and additives with % (w/w) ratios of 100:0:0, 0:100:0, 70:0:30, 40:30:30, and 30:40:30 were tested to determine their antimicrobial activity, cell cytotoxicity, and formaldehyde release. The additives include myristic acid and dibutyl sebacate as plasticizers and butylated hydroxyanisole as an antioxidant. It was observed that the samples containing 70% PAC (PAC7) or 40% PAC (PAC4) with 30% additives had the highest antimicrobial activities against various microbial cells and no cytotoxicity regarding in vitro fibroblast cell growth. In addition, these formulations of adhesive samples released formaldehyde within the levels permitted for medical devices. Taken together, the mixture of PAC and OC as a topical skin adhesive for wound closure was found to be biocompatible, mechanically stable and safe, as well as effective for wound healing.

Snapshot of Phenotypic and Molecular Virulence and Resistance Profiles in Multidrug-Resistant Strains Isolated in a Tertiary Hospital in Romania

A current major healthcare problem is represented by antibiotic resistance, mainly due to multidrug resistant (MDR) Gram negative bacilli (GNB), because of their extended spread both in hospital facilities and in the community's environment. The aim of this study was to investigate the virulence traits of Klebsiella pneumoniae, Acinetobacter baumannii, and Pseudomonas aeruginosa MDR, XDR, and PDR strains isolated from various hospitalized patients. These GNB strains were investigated for the presence of soluble virulence factors (VF), such as hemolysins, lecithinase, amylase, lipase, caseinase, gelatinase, and esculin hydrolysis, as well as for the presence of virulence genes encoding for VF involved in adherence (TC, fimH, and fimA), biofilm formation (algD, ecpRAB, mrkA, mrkD, ompA, and epsA), tissue destruction (plcH and plcN), and in toxin production (cnfI, hlyA, hlyD, and exo complex). All P. aeruginosa strains produced hemolysins; 90% produced lecithinase; and 80% harbored algD, plcH, and plcN genes. The esculin hydrolysis was detected in 96.1% of the K. pneumoniae strains, whereas 86% of them were positive for the mrkA gene. All of the A. baumannii strains produced lecithinase and 80% presented the ompA gene. A significant association was found between the number of VF and the XDR strains, regardless of the isolation sources. This study opens new research perspectives related to bacterial fitness and pathogenicity, and it provides new insights regarding the connection between biofilm formation, other virulence factors, and antibiotic resistance.

The Antimicrobial Peptide Octopromycin Suppresses Biofilm Formation and Quorum Sensing in Acinetobacter baumannii

Acinetobacter baumannii is an opportunistic bacterial pathogen that causes severe infections in immunocompromised individuals. A. baumannii forms biofilm and produces extracellular matrix, which supports bacteria to survive under harsh conditions and be resistant to antibacterial treatments. In the present study, we investigated the biofilm and quorum-sensing inhibitory effects of antimicrobial peptide, octopromycin in A. baumannii. Field emission-scanning electron microscopy results clearly showed significantly reduced biofilm mass and caused a collapse in biofilm architecture at the minimum inhibitory concentration (50 µg/mL) and minimum bactericidal concentration (200 µg/mL) of octopromycin. Antibiotic-resistant persister cells of A. baumannii were successfully killed by octopromycin treatment, and it inhibited violacein production in Chromobacterium violaceum in a concentration-dependent manner. Octopromycin also inhibited alginate production, surface movements (swarming and swimming), and twitching motility of A. baumannnii, confirming its anti-quorum-sensing activity. Multiple metabolic pathways, two-component regulation systems, quorum-sensing, and antibiotic synthesis-related pathways in A. baumannii biofilms were strongly affected by octopromycin treatment. The collective findings indicate that the antibacterial peptide octopromycin may control A. baumannii biofilms through multi-target interactions. Octopromycin could be a desirable therapeutic option for the prevention and control of A. baumannii infections.

Mucus increases cell iron uptake to impact the release of pro-inflammatory mediators after particle exposure

We tested the hypothesis that (1) mucus production can be included in the cell response to iron deficiency; (2) mucus binds iron and increases cell metal uptake; and subsequently (3) mucus impacts the inflammatory response to particle exposure. Using quantitative PCR, RNA for both MUC5B and MUC5AC in normal human bronchial epithelial (NHBE) cells decreased following exposures to ferric ammonium citrate (FAC). Incubation of mucus-containing material collected from the apical surface of NHBE cells grown at air-liquid interface (NHBE-MUC) and a commercially available mucin from porcine stomach (PORC-MUC) with iron demonstrated an in vitro capacity to bind metal. Inclusion of either NHBE-MUC or PORC-MUC in incubations of both BEAS-2B cells and THP1 cells increased iron uptake. Exposure to sugar acids (N-acetyl neuraminic acid, sodium alginate, sodium guluronate, and sodium hyaluronate) similarly increased cell iron uptake. Finally, increased metal transport associated with mucus was associated with a decreased release of interleukin-6 and -8, an anti-inflammatory effect, following silica exposure. We conclude that mucus production can be involved in the response to a functional iron deficiency following particle exposure and mucus can bind metal, increase cell uptake to subsequently diminish or reverse a functional iron deficiency and inflammatory response following particle exposure.

The Bio-Patina on a Hypogeum Wall of the Matera-Sassi Rupestrian Church "San Pietro Barisano" before and after Treatment with Glycoalkaloids

The investigation focused on the deterioration of the walls in the hypogeum of "San Pietro Barisano" rupestrian church, located in the Matera-Sassi (Southern Italy), one of the UNESCO World Heritage sites. The study evaluated the biocide activity of a mixture of natural glycoalkaloids (GAs) extracted from the unripe fruit of Solanum nigrum and applied to clean a hypogeum wall surface in the church affected by bio-patinas. The analyzed bio-patina, collected before treatment and, at pre-established times, after treatment, showed changes in chemical composition detected by XPS, accompanied by visible discoloration and biological activity variation. The biocidal action of the glycoalkaloids mixture, directly employed on the wall surface, was effective after about four weeks for most bio-patina colonizers but not for the fungal species that can migrate and survive in the porosities of the calcarenite. Consequently, the cleaning procedure requires the integration of fungicidal actions, combined with the consolidation of the surfaces, to obtain complete bioremediation and avoid subsequent biological recolonization. SEM images and associated microanalysis of pretreated bio-patina have revealed the biocalcogenity of some autochthonous microorganisms, thus preluding to their eventual isolation and reintroduction on the wall surface to act as consolidants once the bio-cleaning phase has been completed.

The In Vivo and In Vitro Assessment of Pyocins in Treating Pseudomonas aeruginosa Infections

Pseudomonas aeruginosa can cause several life-threatening infections among immunocompromised patients (e.g., cystic fibrosis) due to its ability to adapt and develop resistance to several antibiotics. In recent years, P. aeruginosa infections has become difficult to treat using conventional antibiotics due to the increase multidrug-resistant P. aeruginosa strains. Therefore, there is a growing interest to develop novel treatments against antibiotic-resistance P. aeruginosa strains. One novel method includes the application of antimicrobial peptides secreted by P. aeruginosa strains, known as pyocins. In this review, we will discuss the structure, function, and use of pyocins in the pathogenesis and treatment of P. aeruginosa infection.

ESKAPE Pathogens: Looking at Clp ATPases as Potential Drug Targets

Bacterial antibiotic resistance is rapidly growing globally and poses a severe health threat as the number of multidrug resistant (MDR) and extensively drug-resistant (XDR) bacteria increases. The observed resistance is partially due to natural evolution and to a large extent is attributed to antibiotic misuse and overuse. As the rate of antibiotic resistance increases, it is crucial to develop new drugs to address the emergence of MDR and XDR pathogens. A variety of strategies are employed to address issues pertaining to bacterial antibiotic resistance and these strategies include: (1) the anti-virulence approach, which ultimately targets virulence factors instead of killing the bacterium, (2) employing antimicrobial peptides that target key proteins for bacterial survival and, (3) phage therapy, which uses bacteriophages to treat infectious diseases. In this review, we take a renewed look at a group of ESKAPE pathogens which are known to cause nosocomial infections and are able to escape the bactericidal actions of antibiotics by reducing the efficacy of several known antibiotics. We discuss previously observed escape mechanisms and new possible therapeutic measures to combat these pathogens and further suggest caseinolytic proteins (Clp) as possible therapeutic targets to combat ESKAPE pathogens. These proteins have displayed unmatched significance in bacterial growth, viability and virulence upon chronic infection and under stressful conditions. Furthermore, several studies have showed promising results with targeting Clp proteins in bacterial species, such as Mycobacterium tuberculosis, Staphylococcus aureus and Bacillus subtilis.

Guaiacol augments quorum quenching potential of Ciprofloxacin against Pseudomonas aeruginosa

AIM

The present study aims to investigate the antimicrobial as well as antivirulence potential and the principle mechanism of action of guaiacol against Pseudomonas aeruginosa.

METHODS AND RESULTS

Quorum sensing inhibition and membrane disruption studies were performed to check effect of guaiacol on the virulence of P. aeruginosa. Production of various virulence factors and biofilm formation were studied at sub-MIC concentration of guaiacol alone (1/8 MIC) and in combination with ciprofloxacin (1/2 FIC). Guaiacol exhibited synergistic interactions with ciprofloxacin and further reduced production of all virulence factors and biofilm formation. Using crystal violet (CV) assay and quantification of exopolysaccharide we observed weak biofilm formation, together with reduced motilities at sub MIC which was further visualized by confocal laser microscopy and Field Emission Scanning Electron Microscopy (FESEM).The antibacterial activity of guaiacol against P. aeruginosa upon 2×MIC exposure coincided with enhanced membrane permeability leading to disruption and release of cellular material as quantified by CV uptake assay and Sodium dodecyl suphate-polyacrylamide gel electrophoresis (SDS-PAGE). The results demonstrated that sub MICs of guaiacol in combination with ciprofloxacin can act as a potent alternate compound for attenuation of quorum sensing in P. aeruginosa.

CONCLUSION

Study reports that guaiacol in combination with ciprofloxacin at 1/2 FIC significantly compromised the bacterial growth and motilities alongside inducing quorum quenching potential. This was accompanied by inhibition of biofilm which subsequently decreased EPS production at sub MIC concentration. Furthermore, guaiacol in combination displayed a severe detrimental effect on bacterial membrane disruption, thereby enhancing cellular material release.

SIGNIFICANCE AND IMPACT OF STUDY

For the first time, the potential of guaiacol in combination with ciprofloxacin in attenuation of virulence factors and biofilm formation in P. aeruginosa were described. Results corroborate on how plant bioactive in synergism with antibiotics can act as alternate treatment regime to tackle the menace of drug resistance.

Virulence Factors of Pseudomonas Aeruginosa and Antivirulence Strategies to Combat Its Drug Resistance

Pseudomonas aeruginosa is an opportunistic pathogen causing nosocomial infections in severely ill and immunocompromised patients. Ubiquitously disseminated in the environment, especially in hospitals, it has become a major threat to human health due to the constant emergence of drug-resistant strains. Multiple resistance mechanisms are exploited by P. aeruginosa, which usually result in chronic infections difficult to eradicate. Diverse virulence factors responsible for bacterial adhesion and colonization, host immune suppression, and immune escape, play important roles in the pathogenic process of P. aeruginosa. As such, antivirulence treatment that aims at reducing virulence while sparing the bacterium for its eventual elimination by the immune system, or combination therapies, has significant advantages over traditional antibiotic therapy, as the former imposes minimal selective pressure on P. aeruginosa, thus less likely to induce drug resistance. In this review, we will discuss the virulence factors of P. aeruginosa, their pathogenic roles, and recent advances in antivirulence drug discovery for the treatment of P. aeruginosa infections.

Four decades of experience of prosthetic valve endocarditis reflect a high variety of diverse pathogens

Prosthetic valve endocarditis (PVE) remains a serious condition with a high mortality rate. Precise identification of the PVE-associated pathogen/s and their virulence is essential for successful therapy, and patient survival. The commonly described PVE-associated pathogens are staphylococci, streptococci and enterococci, with Staphylococcus aureus being the most frequently diagnosed species. Furthermore, multi-drug resistance pathogens are increasing in prevalence, and continue to pose new challenges mandating a personalized approach. Blood cultures in combination with echocardiography are the most common methods to diagnose PVE, often being the only indication, it exists. In many cases, the diagnostic strategy recommended in the clinical guidelines does not identify the precise microbial agent and to frequently, false negative blood cultures are reported. Despite the fact that blood culture findings are not always a good indicator of the actual PVE agent in the valve tissue, only a minority of re-operated prostheses are subjected to microbiological diagnostic evaluation. In this review, we focus on the diversity and the complete spectrum of PVE-associated bacterial, fungal and viral pathogens in blood, and prosthetic heart valve, their possible virulence potential, and their challenges in making a microbial diagnosis. We are curious to understand if the unacceptable high mortality of PVE is associated with the high number of negative microbial findings in connection with a possible PVE. Herein, we discuss the possibilities and limits of the diagnostic methods conventionally used and make recommendations for enhanced pathogen identification. We also show possible virulence factors of the most common PVE-associated pathogens and their clinical effects. Based on blood culture, molecular biological diagnostics, and specific valve examination, better derivations for the antibiotic therapy as well as possible preventive intervention can be established in the future.

Efficacy and safety of biofilm dispersal by glycoside hydrolases in wounds

Novel anti-biofilm and dispersal agents are currently being investigated in an attempt to combat biofilm-associated wound infections. Glycoside hydrolases (GHs) are enzymes that hydrolyze the glycosidic bonds between sugars, such as those found within the exopolysaccharides of the biofilm matrix. Previous studies have shown that GHs can weaken the matrix, inducing bacterial dispersal, and improving antibiotic clearance. Yet, the number of GH enzymes that have been examined for potential therapeutic effects is limited. In this study, we screened sixteen GHs for their ability to disperse mono-microbial and polymicrobial biofilms grown in different environments. Six GHs, α-amylase (source: A. oryzae), alginate lyase (source: various algae), pectinase (source: Rhizopus sp.), amyloglucosidase (source: A. niger), inulinase (source: A. niger), and xylanase (source: A. oryzae), exhibited the highest dispersal efficacy in vitro. Two GHs, α-amylase (source: Bacillus sp.) and cellulase (source: A. niger), used in conjunction with meropenem demonstrated infection clearing ability in a mouse wound model. GHs were also effective in improving antibiotic clearance in diabetic mice. To examine their safety, we screened the GHs for toxicity in cell culture. Overall, there was an inverse relationship between enzyme exposure time and cellular toxicity, with twelve out of sixteen GHs demonstrating some level of toxicity in cell culture. However, only one GH exhibited harmful effects in mice. These results further support the ability of GHs to improve antibiotic clearance of biofilm-associated infections and help lay a foundation for establishing GHs as therapeutic agents for chronic wound infections.

Dynamic Constitutional Frameworks as Antibacterial and Antibiofilm Agents

Dynamic constitutional frameworks (DCFs) were synthesized and screened for biofilm inhibition or disruption. They are composed of a trialdehyde core reversibly linked to a diamine PEG connector and to a variety of neutral, anionic, or cationic heads, to generate a library of DCFs to generate multivalent dendritic architectures in the presence of Pseudomonas aeruginosa and Staphylococcus aureus. The best DCFs were always polycationic and the nature of the cationic heads significantly impact the antibiofilm activity. The best antibiofilm activity was observed for DCF3B, displaying a polyethyleneimine head. A simple inactive guanidinium functional head strongly inhibited biofilm growth when assayed as a multivalent DCF3C. Using a more advanced in vitro biofilm model of chronic wound infection, DCF3C was found significantly superior than all other DCFs. These results demonstrate the versatility and effectiveness of DCFs as low cost and efficient systems for antibiofilm disruption.

A fixed-film bioscrubber of Microbacterium esteraromaticum SBS1-7 for toluene/styrene biodegradation

In the present study, a fixed-film bioscrubber (FFBS) of BTEX-degrading bacterium Microbacterium esteraromaticum SBS1-7 with 'AQUAPOROUSGEL® or APG' supporting material was continuously fed with toluene- or styrene-contaminated gas stream for 172 days. Response Surface Methodology (RSM) was used to optimize the biofilm formation on APG as well as the toluene biodegradation in mineral salt medium (MM). The results suggested that 1000 ppm of yeast extract (YE) was necessary for biofilm formation of SBS1-7. The optimized combination of YE and toluene concentration exhibiting the highest biofilm formation and toluene removal was further employed in an up-scale FFBS operation. The maximum Elimination Capacity (EC_max) of 203 g·m^-3·h^-1 was obtained at the toluene Inlet Loading Rate (ILR) of 295 g·m^-3·h^-1. FFBS of SBS1-7 was able to withstand a 5-day shutdown and required only 24 h to recover. Moreover, when the inlet Volatile Organic Compound was shifted to styrene, FFBS required only 24 h for adaptation and the system was able to efficiently remove ~95% of styrene after that. Finally, the performance of the bioscrubber when operated in 2 different modes of operation (FFBS vs Biotricking Filter or BTF) were compared. This study evidently demonstrated the robustness and stability of FFBS with M. esteraromaticum SBS1-7.

Functional Nanomaterials and 3D-Printable Nanocomposite Hydrogels for Enhanced Cell Proliferation and for the Reduction of Bacterial Biofilm Formation

Biomaterial-associated infections are a major cause of biomaterial implant failure. To prevent the initial attachment of bacteria to the implant surface, researchers have investigated various surface modification methods. However, most of these approaches also prevent the attachment, spread, and growth of mammalian cells, resulting in tissue integration failure. Therefore, the success of biomaterial implants requires an optimal balance between tissue integration (cell adhesion to biomaterial implants) and inhibition of bacterial colonization. In this regard, we synthesize bifunctional nanomaterials by functionalizing the pores and outer surfaces of periodic mesoporous organosilica (PMO) with antibacterial tetracycline (Tet) and antibacterial and cell-adhesive bipolymer poly-d-lysine (PDL), respectively. Then, the fabricated ^TetPMO-PDL nanomaterials are incorporated into alginate-based hydrogels to create injectable and 3D-printable nanocomposite (NC) hydrogels (AlgL-^TetPMO-PDL). These bifunctional nanomaterial and 3D-printable NC hydrogel show pH-dependent release of Tet over 7 days. They also enhance the proliferation of eukaryotic cells (fibroblasts). ^TetPMO-PDL is inactive in reducing Pseudomonas aeruginosa, Staphylococcus aureus, and Enterococcus faecalis biofilms. However, AlgL-^TetPMO-PDL shows significant antibiofilm activity against P. aeruginosa. These results suggest that the incorporation of ^TetPMO-PDL into AlgL may have a synergistic effect on the inhibition of the Gram-negative bacterial (P. aeruginosa) biofilm, while this has no effect on the reduction of the Gram-positive bacterial (S. aureus and E. faecalis) biofilm.

Vaccines for multidrug resistant Gram negative bacteria: lessons from the past for guiding future success

Antimicrobial resistance is a major threat to global public health. Vaccination is an effective approach for preventing bacterial infections, however it has not been successfully applied to infections caused by some of the most problematic multidrug resistant pathogens. In this review, the potential for vaccines to contribute to reducing the burden of disease of infections caused by multidrug resistant Gram negative bacteria is presented. Technical, logistical and societal hurdles that have limited successful vaccine development for these infections in the past are identified, and recent advances that can contribute to overcoming these challenges are assessed. A synthesis of vaccine technologies that have been employed in the development of vaccines for key multidrug resistant Gram negative bacteria is included, and emerging technologies that may contribute to future successes are discussed. Finally, a comprehensive review of vaccine development efforts over the last 40 years for three of the most worrisome multidrug resistant Gram negative pathogens, Acinetobacter baumannii, Klebsiella pneumoniae and Pseudomonas aeruginosa is presented, with a focus on recent and ongoing studies. Finally, future directions for the vaccine development field are highlighted.

Cryptic surface-associated multicellularity emerges through cell adhesion and its regulation

The repeated evolution of multicellularity led to a wide diversity of organisms, many of which are sessile, including land plants, many fungi, and colonial animals. Sessile organisms adhere to a surface for most of their lives, where they grow and compete for space. Despite the prevalence of surface-associated multicellularity, little is known about its evolutionary origin. Here, we introduce a novel theoretical approach, based on spatial lineage tracking of cells, to study this origin. We show that multicellularity can rapidly evolve from two widespread cellular properties: cell adhesion and the regulatory control of adhesion. By evolving adhesion, cells attach to a surface, where they spontaneously give rise to primitive cell collectives that differ in size, life span, and mode of propagation. Selection in favor of large collectives increases the fraction of adhesive cells until a surface becomes fully occupied. Through kin recognition, collectives then evolve a central-peripheral polarity in cell adhesion that supports a division of labor between cells and profoundly impacts growth. Despite this spatial organization, nascent collectives remain cryptic, lack well-defined boundaries, and would require experimental lineage tracking technologies for their identification. Our results suggest that cryptic multicellularity could readily evolve and originate well before multicellular individuals become morphologically evident.

AlgU, a Conserved Sigma Factor Regulating Abiotic Stress Tolerance and Promoting Virulence in Pseudomonas syringae

Pseudomonas syringae can rapidly deploy specialized functions to deal with abiotic and biotic stresses. Host niches pose specific sets of environmental challenges driven, in part, by immune defenses. Bacteria use a "just-in-time" strategy of gene regulation, meaning that they only produce the functions necessary for survival as needed. Extracytoplasmic function (ECF) sigma factors transduce a specific set of environmental signals and change gene expression patterns by altering RNA polymerase promoter specificity, to adjust bacterial physiology, structure, or behavior, singly or in combination, to improve chances of survival. The broadly conserved ECF sigma factor AlgU affects virulence in both animal and plant pathogens. Pseudomonas syringae AlgU controls expression of more than 800 genes, some of which contribute to suppression of plant immunity and bacterial fitness in plants. This review discusses AlgU activation mechanisms, functions controlled by AlgU, and how these functions contribute to P. syringae survival in plants.[Formula: see text] The author(s) have dedicated the work to the public domain under the Creative Commons CC0 "No Rights Reserved" license by waiving all of his or her rights to the work worldwide under copyright law, including all related and neighboring rights, to the extent allowed by law. 2021.

The role of extracellular DNA in the formation, architecture, stability, and treatment of bacterial biofilms

Advances in biotechnology to treat and cure human disease have markedly improved human health and the development of modern societies. However, substantial challenges remain to overcome innate biological factors that thwart the activity and efficacy of pharmaceutical therapeutics. Until recently, the importance of extracellular DNA (eDNA) in biofilms was overlooked. New data reveal its extensive role in biofilm formation, adhesion, and structural integrity. Different approaches to target eDNA as anti-biofilm therapies have been proposed, but eDNA and the corresponding biofilm barriers are still difficult to disrupt. Therefore, more creative approaches to eradicate biofilms are needed. The production of eDNA often originates with the genetic material of bacterial cells through cell lysis. However, genomic DNA and eDNA are not necessarily structurally or compositionally identical. Variations are noteworthy because they dictate important interactions within the biofilm. Interactions between eDNA and biofilm components may as well be exploited as alternative anti-biofilm strategies. In this review, we discuss recent developments in eDNA research, emphasizing potential ways to disrupt biofilms. This review also highlights proteins, exopolysaccharides, and other molecules interacting with eDNA that can serve as anti-biofilm therapeutic targets. Overall, the array of diverse interactions with eDNA is important in biofilm structure, architecture, and stability.

Anti-quorum sensing and antibiofilm potential of 1,8-cineole derived from Musa paradisiaca against Pseudomonas aeruginosa strain PAO1

Pseudomonas aeruginosa is one of the vulnerable opportunistic pathogens associated with nosocomial infections, cystic fibrosis, burn wounds and surgical site infections. Several studies have reported that quorum sensing (QS) systems are controlled the P. aeruginosa pathogenicity. Hence, the targeting of QS considered as an alternative approach to control P. aeruginosa infections. This study aimed to evaluate the anti-quorum sensing and antibiofilm inhibitory potential of Musa paradisiaca against Chromobacterium violaceum (ATCC 12472) and Pseudomonas aeruginosa. The methanol extract of M. paradisiacsa exhibits that better antibiofilm potential against P. aeruginosa. Then, the crude methanol extract was subjected to purify by column chromatography and collected the fractions. The mass-spectrometric analysis of a methanol extract of M. paradisiaca revealed that 1,8-cineole is the major compounds. 1, 8-cineole significantly inhibited the QS regulated violacein production in C. violaceum. Moreover, 1,8-cineole significantly inhibited the QS mediated virulence production and biofilm formation of P. aeruginosa without affecting their growth. The real-time PCR analysis showed the downregulation of autoinducer synthase and transcriptional regulator genes upon 1,8-cineole treatment. The findings of the present study strongly suggested that metabolite of M. paradisiaca impedes P. aeruginosa QS system and associated virulence productions.

Naringin inhibits the biofilms of metallo-β-lactamases (MβLs) producing Pseudomonas species isolated from camel meat

Food producing animals harbouring bacteria carrying drug resistance genes especially the metallo-beta-lactamase (MBL) pose high risk for the human population. In addition, formation of biofilm by these drug resistant pathogens represents major threat to food safety and public health. In this study, metallo-β-lactamases (MβLs) producing Pseudomonas spp. from camel meat were isolated and assessed for their biofilm formation. Further, in vitro and in silico studies were performed to study the effect of flavone naringin on biofilm formation against isolated Pseudomonas spp. A total of 55% isolates were found to produce metallo-β-lactamase enzyme. Naringin mitigated biofilm formation of Pseudomonas isolates up to 57%. Disturbed biofilm architecture and reduced the colonization of bacteria on glass was observed under scanning electron microscope (SEM) and confocal laser scanning microscope (CLSM). The biofilm related traits such as exopolysaccharides (EPS) and alginate production was also reduced remarkably in the presence of naringin. Eradication of preformed biofilms (32–60%) was also observed at the respective 0.50 × MICs. Molecular docking revealed that naringin showed strong affinity towards docked proteins with binding energy ranging from −8.6 to −8.8 kcal mol⁻¹. Presence of metallo-β-lactamase producers indicates that camel meat could be possible reservoir of drug-resistant Pseudomonas species of clinical importance. Naringin was successful in inhibiting biofilm formation as well as eradicating the preformed biofilms and demonstrated strong binding affinity towards biofilm associated protein. Thus, it is envisaged that naringin could be exploited as food preservative especially against the biofilm forming food-borne Pseudomonas species and is a promising prospect for the treatment of biofilm based infections.

Structural changes in model compounds of sludge extracellular polymeric substances caused by exposure to free nitrous acid

Previous studies demonstrate that free nitrous acid (FNA i.e. HNO₂) detaches sewer biofilms, breaks down flocs of waste activated sludge (WAS) and enhances biogas production from WAS. This suggests possible interactions of FNA with organic extracellular polymeric substances (EPS) that bind the cells into biofilms or sludge flocs. This study evaluates the chemical interactions and reaction mechanisms between FNA and molecules representative of key EPS in biofilm and sludge flocs. Molecules chosen to represent components found in the extracellular polymeric matrix were treated with FNA at 6.09 mgN/L (NO₂^- = 250 mgN/L, pH = 5.0 ± 0.2, T = 22 °C) for 24 hours (conditions typically used in applications) so as to consider the hypothesized chemical interactions and the consequent reaction pathways. A number of analytical techniques were employed to measure the molecular changes in the EPS molecules including; proton (¹H) nuclear magnetic resonance spectroscopy (NMR), electrospray ionisation mass spectrometry (ESI-MS) and gel permeation chromatography (GPC). The results demonstrated that FNA broke down a range of large EPS molecules including carbohydrates, protein and lipids to smaller molecules. Two mechanistic pathways have been proposed including electrophilic substitution, whereby the nitrosium ion (NO⁺) was the reactive electrophile, and oxidative radical reactions, through which the nitrogen radicals (^.NO₂, ^.NO) and reactive nitrogen intermediates (RNIs) (e.g. N₂O₃ and N₂O₄) formed from the decomposition of FNA became part of the reaction products. Larger, more complex organic molecules such as humic acid, required higher concentrations of FNA (6.09 mgN/L or greater) to cause molecular breakdown, whereas smaller molecules, such as calcium alginate, was broken down at lower concentrations (3.04 mgN/L). The study contributes to the understanding of the fundamental mechanisms behind the application of FNA for biofilm control and flocular sludge disintegration.

Nitrite production by ammonia-oxidizing bacteria mediates chloramine decay and resistance in a mixed-species community

As water distribution centres increasingly switch to using chloramine to disinfect drinking water, it is of paramount importance to determine the interactions of chloramine with potential biological contaminants, such as bacterial biofilms, that are found in these systems. For example, ammonia-oxidizing bacteria (AOB) are known to accelerate the decay of chloramine in drinking water systems, but it is also known that organic compounds can increase the chloramine demand. This study expanded upon our previously published model to compare the decay of chloramine in response to alginate, Pseudomonas aeruginosa, Nitrosomonas europaea and a mixed-species nitrifying culture, exploring the contributions of microbial by-products, heterotrophic bacteria and AOBs to chloramine decay. Furthermore, the contribution of AOBs to biofilm stability during chloramination was investigated. The results demonstrate that the biofilm matrix or extracellular polymeric substances (EPS), represented by alginate in these experiments, as well as high concentrations of dead or inactive cells, can drive chloramine decay rather than any specific biochemical activity of P. aeruginosa cells. Alginate was shown to reduce chloramine concentrations in a dose-dependent manner at an average rate of 0.003 mg l-1  h-1 per mg l-1 of alginate. Additionally, metabolically active AOBs mediated the decay of chloramine, which protected members of mixed-species biofilms from chloramine-mediated disinfection. Under these conditions, nitrite produced by AOBs directly reacted with chloramine to drive its decay. In contrast, biofilms of mixed-species communities that were dominated by heterotrophic bacteria due to either the absence of ammonia, or the addition of nitrification inhibitors and glucose, were highly sensitive to chloramine. These results suggest that mixed-species biofilms are protected by a combination of biofilm matrix-mediated inactivation of chloramine as well as the conversion of ammonia to nitrite through the activity of AOBs present in the community.

Secondary Effects of Antibiotics on Microbial Biofilms

Biofilms are assemblages of microorganisms attached to each other, or to a surface, and encased in a protective, self-produced matrix. Such associations are now recognized as the predominant microbial growth mode. The physiology of cells in biofilms differs from that of the planktonic cells on which most research has been conducted. Consequently, there are significant gaps in our knowledge of the biofilm lifestyle. Filling this gap is particularly important, given that biofilm cells may respond differently to antibiotics than do planktonic cells of the same species. Understanding the effects of antibiotics on biofilms is of paramount importance for clinical practice due to the increased levels of antibiotic resistance and resistance dissemination in biofilms. From a wider environmental perspective antibiotic exposure can alter the ecology of biofilms in nature, and hence disrupt ecosystems. Biofilm cells display increased resilience toward antibiotics. This resilience is often explained by mechanisms and traits such as decreased antibiotic penetration, metabolically inactive persister cells, and intrinsic resistance by members of the biofilm community. Together, these factors suggest that cells in biofilms are often exposed to subinhibitory concentrations of antimicrobial agents. Here we discuss how cells in biofilms are affected by the presence of antibiotics at subinhibitory concentrations, and the possible ramifications of such secondary effects for healthcare and the environment.

2,4-Di-Tert-Butylphenol Isolated From an Endophytic Fungus, Daldinia eschscholtzii, Reduces Virulence and Quorum Sensing in Pseudomonas aeruginosa

Pseudomonas aeruginosa is among the top three gram-negative bacteria according to the WHO’s critical priority list of pathogens against which newer antibiotics are urgently needed and considered a global threat due to multiple drug resistance. This situation demands unconventional antimicrobial strategies such as the inhibition of quorum sensing to alleviate the manifestation of classical resistance mechanisms. Here, we report that 2,4-di-tert-butylphenol (2,4-DBP), isolated from an endophytic fungus, Daldinia eschscholtzii, inhibits the quorum-sensing properties of P. aeruginosa. We have found that treating P. aeruginosa with 2,4-DBP substantially reduced the secretion of virulence factors as well as biofilm, and its associated factors that are controlled by quorum sensing, in a dose-dependent manner. Concomitantly, 2,4-DBP also significantly reduced the expression of quorum sensing-related genes, i.e., lasI, lasR, rhlI, and rhlR significantly. Importantly, 2,4-DBP restricted the adhesion and invasion of P. aeruginosa to the A549 lung alveolar carcinoma cells. In addition, bactericidal assay with 2,4-DBP exhibited synergism with ampicillin to kill P. aeruginosa. Furthermore, our computational studies predicted that 2,4-DBP could bind to the P. aeruginosa quorum-sensing receptors LasR and RhlR. Collectively, these data suggest that 2,4-DBP can be exploited as a standalone drug or in combination with antibiotic(s) as an anti-virulence and anti-biofilm agent to combat the multidrug resistant P. aeruginosa infection.

Alginate Affects Bioactivity of Chimeric Collagen-Binding LL37 Antimicrobial Peptides Adsorbed to Collagen-Alginate Wound Dressings

Chronic infected wounds cause more than 23,000 deaths annually. Antibiotics and antiseptics are conventionally used to treat infected wounds; however, they can be toxic to mammalian cells, and their use can contribute to antimicrobial resistance. Antimicrobial peptides (AMPs) have been utilized to address the limitations of antiseptics and antibiotics. In previous work, we modified the human AMP LL37 with collagen-binding domains from collagenase (cCBD) or fibronectin (fCBD) to facilitate peptide tethering and delivery from collagen-based wound dressings. We found that cCBD-LL37 and fCBD-LL37 were retained and active when bound to 100% collagen scaffolds. Collagen wound dressings are commonly made as composites with other materials, such as alginate. The goal of this study was to investigate how the presence of alginate affects the tethering, release, and antimicrobial activity of LL37 and CBD-LL37 peptides adsorbed to commercially available collagen-alginate wound dressings (FIBRACOL Plus-a 90% collagen and 10% alginate wound dressing). We found that over 85% of the LL37, cCBD-LL37, and fCBD-LL37 was retained on FIBRACOL Plus over a 14-day release study (90.3, 85.8, and 98.6%, respectively). Additionally, FIBRACOL Plus samples loaded with peptides were bactericidal toward Pseudomonas aeruginosa, even after 14 days in release buffer but demonstrated no antimicrobial activity against Escherichia coli, Staphylococcus aureus, and Staphylococcus epidermidis. The presence of alginate in solution induced conformational changes in the cCBD-LL37 and LL37 peptides, resulting in increased peptide helicity, and reduced antimicrobial activity against P. aeruginosa. Peptide-loaded FIBRACOL Plus scaffolds were not cytotoxic to human dermal fibroblasts. This study demonstrates that CBD-mediated LL37 tethering is a viable strategy to reduce LL37 toxicity, and how substrate composition plays a crucial role in modulating the antimicrobial activity of tethered AMPs.

Virulence attenuating combination therapy: a potential multi-target synergy approach to treat Pseudomonas aeruginosa infections in cystic fibrosis patients

The World Health Organization considers the discovery of new treatments for P. aeruginosa a top priority. Virulence attenuating combination therapy (VACT) is a pragmatic strategy to improve bacterial clearance, repurpose outmoded antibiotics, improve drug efficacy at lower doses, and reduce the evolution of resistance. In vitro and in vivo studies have shown that adding a quorum sensing inhibitor or an extracellular polymeric substance repressor to classical antibiotics synergistically improves antipseudomonal activity. This review highlights why VACT could specifically benefit cystic fibrosis patients harboring chronic P. aeruginosa infections, outlines the current landscape of synergistic combinations between virulence-targeting small-molecules and anti-pseudomonal drugs, and suggests future directions for VACT research.

Flexible Hierarchical Wraps Repel Drug-Resistant Gram-Negative and Positive Bacteria

Healthcare acquired infections are a major human health problem, and are becoming increasingly troublesome with the emergence of drug resistant bacteria. Engineered surfaces that reduce the adhesion, proliferation, and spread of bacteria have promise as a mean of preventing infections and reducing the use of antibiotics. To address this need, we created a flexible plastic wrap that combines a hierarchical wrinkled structure with chemical functionalization to reduce bacterial adhesion, biofilm formation, and the transfer of bacteria through an intermediate surface. These hierarchical wraps were effective for reducing biofilm formation of World Health Organization-designated priority pathogens Gram positive methicillin-resistant Staphylococcus aureus (MRSA) and Gram negative Pseudomonas aeruginosa by 87 and 84%, respectively. In addition, these surfaces remain free of bacteria after being touched by a contaminated surface with Gram negative E. coli. We showed that these properties are the result of broad liquid repellency of the engineered surfaces and the presence of reduced anchor points for bacterial adhesion on the hierarchical structure. Such wraps are fabricated using scalable bottom-up techniques and form an effective cover on a variety of complex objects, making them superior to top-down and substrate-specific surface modification methods.

2,4-Di-Tert-Butylphenol Isolated From an Endophytic Fungus, Daldinia eschscholtzii, Reduces Virulence and Quorum Sensing in Pseudomonas aeruginosa

Pseudomonas aeruginosa is among the top three gram-negative bacteria according to the WHO's critical priority list of pathogens against which newer antibiotics are urgently needed and considered a global threat due to multiple drug resistance. This situation demands unconventional antimicrobial strategies such as the inhibition of quorum sensing to alleviate the manifestation of classical resistance mechanisms. Here, we report that 2,4-di-tert-butylphenol (2,4-DBP), isolated from an endophytic fungus, Daldinia eschscholtzii, inhibits the quorum-sensing properties of P. aeruginosa. We have found that treating P. aeruginosa with 2,4-DBP substantially reduced the secretion of virulence factors as well as biofilm, and its associated factors that are controlled by quorum sensing, in a dose-dependent manner. Concomitantly, 2,4-DBP also significantly reduced the expression of quorum sensing-related genes, i.e., lasI, lasR, rhlI, and rhlR significantly. Importantly, 2,4-DBP restricted the adhesion and invasion of P. aeruginosa to the A549 lung alveolar carcinoma cells. In addition, bactericidal assay with 2,4-DBP exhibited synergism with ampicillin to kill P. aeruginosa. Furthermore, our computational studies predicted that 2,4-DBP could bind to the P. aeruginosa quorum-sensing receptors LasR and RhlR. Collectively, these data suggest that 2,4-DBP can be exploited as a standalone drug or in combination with antibiotic(s) as an anti-virulence and anti-biofilm agent to combat the multidrug resistant P. aeruginosa infection.

Structure of the active GGEEF domain of a diguanylate cyclase from Vibrio cholerae

Cyclic-di-GMP (c-di-GMP) synthesized by diguanylate cyclases has been an important and ubiquitous secondary messenger in almost all bacterial systems. In Vibrio cholerae, c-di-GMP plays an intricate role in the production of the exopolysaccharide matrix, and thereby, in biofilm formation. The formation of the surface biofilm enables the bacteria to survive in aquatic bodies, when not infecting a human host. Diguanylate cyclases are the class of enzymes which synthesize c-di-GMP from two molecules of GTP and are endowed with a GGDEF or, a GGEEF signature domain. The VC0395_0300 protein from V. cholerae, has been established as a diguanylate cyclase with a necessary role in biofilm formation. Here we present the structure of an N-terminally truncated form of VC0395_0300, which retains the active GGEEF domain for diguanylate cyclase activity but lacks 160 residues from the poorly organized N-terminal domain. X-ray diffraction data was collected from a crystal of VC0395_0300_(161-321) to a resolution of 1.9 Å. The structure displays remarkable topological similarity with diguanylate cyclases from other bacterial systems, but lacks the binding site for c-di-GMP present in its homologues. Finally, we demonstrate the ability of the truncated diguanylate cyclase VC0395_0300_(161-321) to produce c-di-GMP, and its role in biofilm formation for the bacteria.

The feasibility of using Saffron to reduce the photosensitivity reaction of selected photosensitizers using red blood cells and staphylococcusAureus bacteria as targets

BACKGROUND

The photosensitivity reaction which appears after a Photodynamic therapy treatment session is a challenge that needs further investigation. The goal of this research is to evaluate the possibility of using saffron to reduce or control this photosensitivity reaction and to present mathematical modeling of the cell survival curves and their dependency on saffron concentration.

METHODS

Red blood cells (RBC) and Staphylococcus aureus Bacteria (STB) were used as targets in this study. The Photosensitivity of Rose Bengali, Methylene Blue, and Photofrin independently and incorporated with saffron was investigated for continued irradiation at different Saffron concentrations. Gompertz's function was used to fit the survival curve parameters. The 50% cell survival rate was fit to an empirical formula based on Saffron concentrations.

RESULTS

Saffron inhibits the photosensitivity reaction of the three photosensitizers and causes a significant increase in the 50% survival rate time (t₅₀) for RBC`s and STB. Saffron didn't show phototoxicity when incubated alone with RBC`s and STB. The survival curve parameters of the RBCs and STB showed a good fit to the Gompertz function. Saffron concentration is related to the RBC`s t₅₀ based on power dependency of 0.56, 0.38 and 0.31 for Photofrin, Methylene Blue and Rose Bengali respectively and 0.1 on STB for Rose Bengali.

CONCLUSION

Saffron can efficiently be used to reduce the photosensitivity reaction of Photosensitizers after a PDT treatment session. Gompertz function was found to be an appropriate mathematical model for survival rate curves. The t₅₀ and the saffron concentration are well related through a power dependence empirical formula.

In situ surface modification on dental composite resin using 2-methacryloyloxyethyl phosphorylcholine polymer for controlling plaque formation

Composite resins (CRs) are widely used as dental restorative materials for caries treatment. They cause problems of secondary caries since Streptococcus mutans stays in the dental plaque, which the surface exists and produces acidic compounds during metabolism. The dental plaque depositions are induced by the protein adsorption on the surface. Therefore, suppression of protein adsorption on the surface of the CRs is important for inhibiting the formation of plaque and secondary caries. In this study we developed a surface treatment to provide an antibiofouling nature to the CRs by chemical reaction with 2-methacryloyloxyethyl phosphorylcholine (MPC) polymers in the oral cavity during dental treatment. To carry out the photochemical reaction on the remaining polymerizable groups of CRs, we synthesized the MPC polymer with a polymerizable group in the side chain. The MPC polymer could bind on the surfaces of the CRs chemically under dental treatment procedures. The treated surface showed significant resistance to oral protein adsorption and bacterial adhesion even when the surface was brushed with a toothbrush. Thus, we concluded that the photochemical reaction of the MPC polymer with the CRs in the oral cavity was good for making an antibiofouling surface and preventing secondary caries.

Structural studies on bacterial system used in the recognition and uptake of the macromolecule alginate

Alginate is an acidic heteropolysaccharide produced by brown seaweed and certain kinds of bacteria. The cells of Sphingomonas sp. strain A1, a gram-negative bacterium, have several alginate-degrading enzymes in their cytoplasm and efficiently utilize this polymer for their growth. Sphingomonas sp. strain A1 cells can directly incorporate alginate into their cytoplasm through a transport system consisting of a "pit" on their cell surface, substrate-binding proteins in their periplasm, and an ATP-binding cassette transporter in their inner membrane. This review deals with the structural and functional aspects of bacterial systems necessary for the recognition and uptake of alginate.

On the sensitivity of alginate rheology to composition

The linear response of alginate-phenyl boronic acid (Alg-PBA) esters shows a universal, composition-independent viscoelastic fluid-like behaviour. Reversible association of alginates governs their rheology at all compositions (viz. at all alginate concentrations and solution pH). However, their high strain behaviour is very sensitive to composition. Tuning composition affords liquids that neck to form filaments capable of being drawn to large elongations without failure. We interpret our data by invoking strain-dependent association and dissociation rates for the alginates. High association rates at high strain result in materials with viscoelastic liquid like behaviour.

Exposure to low doses of UVA increases biofilm formation in Pseudomonas aeruginosa

The establishment of bacterial biofilms on abiotic surfaces is a complex process regulated by multiple genetic regulators and environmental factors which are able to modulate the passage of planktonic cells to a sessile state. Solar ultraviolet-A radiation (UVA, 315-400) is one of the main environmental stress factors that bacteria must face at the Earth´s surface. The deleterious effects of UVA are mainly due to oxidative damage. This paper reports that exposure to low UVA doses promotes biofilm formation in three prototypical strains of Pseudomonas aeruginosa, a relevant opportunistic human pathogen. It demonstrates that exposure of planktonic cells to sublethal doses of UVA can increase cell surface hydrophobicity and swimming motility, two parameters known to favor cell adhesion. These results suggest that UVA radiation acts, at least in part, by promoting the first stages of biofilm development.

Viscoelastic properties of Pseudomonas aeruginosa variant biofilms

Pseudomonas aeruginosa evolves during chronic pulmonary infections of cystic fibrosis (CF) patients, forming pathoadapted variants that are persistent. Mucoid and rugose small-colony variants (RSCVs) are typically isolated from sputum of CF patients. These variants overproduce exopolysaccharides in the biofilm extracellular polymeric substance (EPS). Currently, changes to the biophysical properties of RSCV and mucoid biofilms due to variations in EPS are not well understood. This knowledge may reveal how lung infections resist host clearance mechanisms. Here, we used mechanical indentation and shear rheometry to analyse the viscoelasticity of RSCV and mucoid colony-biofilms compared to their isogenic parent at 2-, 4-, and 6-d. While the viscoelasticity of parental colony-biofilms underwent fluctuating temporal changes, in contrast, RSCV and mucoid colony-biofilms showed a gradual progression to more elastic-solid behaviour. Theoretical indices of mucociliary and cough clearance predict that mature 6-d parental and RSCV biofilms may show reduced cough clearance from the lung, while early mucoid biofilms may show reduced clearance by both mechanisms. We propose that viscoelasticity be considered a virulence property of biofilms.