Quorum-sensing genes in Pseudomonas aeruginosa biofilms: their role and expression patterns

Bacillus Strains as Effective Biocontrol Agents Against Phytopathogenic Bacteria and Promoters of Plant Growth

Modern crop production relies on the application of chemical pesticides and fertilizers causing environmental and economic challenges. In response, less environmentally impactful alternatives have emerged such as the use of beneficial microorganisms. These microorganisms, particularly plant growth-promoting bacteria (PGPB), have demonstrated their ability to enhance plant growth, protect against various stresses, and reduce the need for chemical inputs. Among the PGPB, Bacillus species have garnered attention due to their adaptability and commercial potential. Recent reports have highlighted Bacillus strains as biocontrol agents against phytopathogenic bacteria while concurrently promoting plant growth. We also examined Bacillus plant growth-promoting abilities in Arabidopsis thaliana seedlings. In this study, we assessed the potential of various Bacillus strains to control diverse phytopathogenic bacteria and inhibit quorum sensing using Chromobacterium violaceum as a model system. In conclusion, our results suggest that bacteria of the genus Bacillus hold significant potential for biotechnological applications. This includes developments aimed at reducing agrochemical use, promoting sustainable agriculture, and enhancing crop yield and protection.

Development of an analytical method to quantify N-acyl-homoserine lactones in bacterial cultures, river water, and treated wastewater

N-Acyl-homoserine lactones (AHL) play a major role in the communication of Gram-negative bacteria. They influence processes such as biofilm formation, swarming motility, and bioluminescence in the aquatic environment. A comprehensive analytical method was developed to elucidate the "chemical communication" in pure bacterial cultures as well as in the aquatic environment and engineered environments with biofilms. Due to the high diversity of AHLs and their low concentrations in water, a sensitive and selective LC-ESI-MS/MS method combined with solid-phase extraction was developed for 34 AHLs, optimized and validated to quantify AHLs in bacterial conditioned medium, river water, and treated wastewater. Furthermore, the developed method was optimized in terms of enrichment volume, internal standards, limits of detection, and limits of quantification in several matrices. An unanticipated variety of AHLs was detected in the culture media of Pseudomonas aeruginosa (in total 8 AHLs), Phaeobacter gallaeciensis (in total 6 AHLs), and Methylobacterium mesophilicum (in total 15 AHLs), which to our knowledge have not been described for these bacterial cultures so far. Furthermore, AHLs were detected in river water (in total 5 AHLs) and treated wastewater (in total 3 AHLs). Several detected AHLs were quantified (in total 24) using a standard addition method up to 7.3±1.0 µg/L 3-Oxo-C12-AHL (culture media of P. aeruginosa).

Long-duration environmental biosensing by recording analyte detection in DNA using recombinase memory

Microbial biosensors that convert environmental information into real-time visual outputs are limited in their sensing abilities in complex environments, such as soil and wastewater, due to optical inaccessibility. Biosensors that could record transient exposure to analytes within a large time window for later retrieval represent a promising approach to solve the accessibility problem. Here, we test the performance of recombinase-memory biosensors that sense a sugar (arabinose) and a microbial communication molecule (3-oxo-C12-L-homoserine lactone) over 8 days (~70 generations) following analyte exposure. These biosensors sense the analyte and trigger the expression of a recombinase enzyme which flips a segment of DNA, creating a genetic memory, and initiates fluorescent protein expression. The initial designs failed over time due to unintended DNA flipping in the absence of the analyte and loss of the flipped state after exposure to the analyte. Biosensor performance was improved by decreasing recombinase expression, removing the fluorescent protein output, and using quantitative PCR to read out stored information. Application of memory biosensors in wastewater isolates achieved memory of analyte exposure in an uncharacterized Pseudomonas isolate. By returning these engineered isolates to their native environments, recombinase-memory systems are expected to enable longer duration and in situ investigation of microbial signaling, cross-feeding, community shifts, and gene transfer beyond the reach of traditional environmental biosensors.IMPORTANCEMicrobes mediate ecological processes over timescales that can far exceed the half-lives of transient metabolites and signals that drive their collective behaviors. We investigated strategies for engineering microbes to stably record their transient exposure to a chemical over many generations through DNA rearrangements. We identify genetic architectures that improve memory biosensor performance and characterize these in wastewater isolates. Memory biosensors are expected to be useful for monitoring cell-cell signals in biofilms, detecting transient exposure to chemical pollutants, and observing microbial cross-feeding through short-lived metabolites within cryptic methane, nitrogen, and sulfur cycling processes. They will also enable in situ studies of microbial responses to ephemeral environmental changes, or other ecological processes that are currently challenging to monitor non-destructively using real-time biosensors and analytical instruments.

Cultural techniques capture diverse phosphate-solubilizing bacteria in rock phosphate-enriched habitats

Phosphorus (P) deficiency is a common problem in croplands where phosphate-based fertilizers are regularly used to maintain bioavailable P for plants. However, due to their limited mobility in the soil, there has been an increased interest in microorganisms that can convert insoluble P into a bioavailable form, and their use to develop phosphate-solubilizing bioinoculants as an alternative to the conventional use of P fertilizers. In this study, we proposed two independent experiments and explored two entirely different habitats to trap phosphate-solubilizing bacteria (PSBs). In the first experiment, PSBs were isolated from the rhizoplane of native plant species grown in a rock-phosphate (RP) mining area. A subset of 24 bacterial isolates from 210 rhizoplane morphotypes was selected for the inorganic phosphate solubilizing activities using tricalcium phosphate (TCP) as the sole P source. In the second experiment, we proposed an innovative experimental setup to select mycohyphospheric bacteria associated to arbuscular mycorrhizal fungal hyphae, indigenous of soils where agronomic plant have been grown and trapped in membrane bag filled with RP. A subset of 25 bacterial isolates from 44 mycohyphospheric morphotypes was tested for P solubilizing activities. These two bacterial subsets were then screened for additional plant growth-promoting (PGP) traits, and 16S rDNA sequencing was performed for their identification. Overall, the two isolation experiments resulted in diverse phylogenetic affiliations of the PSB collection, showing only 4 genera (24%) and 5 species (17%) shared between the two communities, thus underlining the value of the two protocols, including the innovative mycohyphospheric isolate selection method, for selecting a greater biodiversity of cultivable PSB. All the rhizoplane and mycohyphospheric PSB were positive for ammonia production. Indol-3-acetic acid (IAA) production was observed for 13 and 20 isolates, respectively among rhizoplane and mycohyphospheric PSB, ranging, respectively, from 32.52 to 330.27 μg mL-1 and from 41.4 to 963.9 μg mL-1. Only five rhizoplane and 12 mycohyphospheric isolates were positively screened for N2 fixation. Four rhizoplane PSB were identified as siderophore producers, while none of the mycohyphospheric isolates were. The phenotype of one PSB rhizoplane isolate, assigned to Pseudomonas, showed four additive PGP activities. Some bacterial strains belonging to the dominant genera Bacillus and Pseudomonas could be considered potential candidates for further formulation of biofertilizer in order to develop bioinoculant consortia that promote plant P nutrition and growth in RP-enriched soils.

Isolation of a quorum quenching bacterium effective to various acyl-homoserine lactones: Its quorum quenching mechanism and application to a membrane bioreactor

Biofouling, caused by microbial biofilm formation on the membrane surface and in pores, is a major operational problem in membrane bioreactors (MBR). Many quorum quenching (QQ) bacteria have been isolated and applied to MBR to reduce biofouling. However, for more effective MBR biofouling control, novel approaches for isolating QQ bacteria and applying them in MBR are needed. Therefore, Listeria grayi (HEMM-2) was isolated using a mixture of different N-acyl homoserine lactones (AHLs). HEMM-2 degraded various AHLs, regardless of the length and oxo group in the carbon chain, with quorum sensing (QS) inhibition ratios of 47-61%. This QQ activity was attributed to extracellular substances in HEMM-2 cell-free supernatant (CFS). Furthermore, the HEMM-2 CFS negatively regulated QS-related gene expression, inhibiting Pseudomonas aeruginosa and activated sludge-biofilm formation by 53-75%. Surprisingly, when the HEMM-2 CFS was directly injected into a laboratory-scale MBR system, biofouling was not significantly affected. Biofouling was only controlled by cell suspension (CS) of HEMM-2, indicating the importance of QQ bacteria in MBR. The HEMM-2 CS increased operation time to reach 0.4 bar, a threshold transmembrane pressure for complete biofouling, from 315 h to 371 h. Taken together, HEMM-2, which is effective in the degradation of various AHLs, and its applicable method to MBR may be considered a potent approach for controlling biofouling and understanding the behavior of QQ bacteria in MBR systems.

Investigating the Role of Metabolism for Antibiotic Combination Therapies in Pseudomonas aeruginosa

Antibacterial resistance poses a severe threat to public health; an anticipated 14-fold increase in multidrug-resistant (MDR) bacterial infections is expected to occur by 2050. Contrary to antibiotics, combination therapies are the standard of care for antiviral and anticancer treatments, as synergistic drug-drug interactions can decrease dosage and resistance development. In this study, we investigated combination treatments of a novel succinate dehydrogenase inhibitor (promysalin) with specific inhibitors of metabolism and efflux alongside a panel of clinically approved antibiotics in synergy studies. Through these investigations, we determined that promysalin can work synergistically with vancomycin and antagonistically with aminoglycosides and a glyoxylate shunt pathway inhibitor at subinhibitory concentrations; however, these cooperative effects do not reduce minimum inhibitory concentrations. The variability of these results underscores the complexity of targeting metabolism for combination therapies in antibiotic development.

Bile effects on the Pseudomonas aeruginosa pathogenesis in cystic fibrosis patients with gastroesophageal reflux

Gastroesophageal reflux (GER) occurs in most cystic fibrosis (CF) patients and is the primary source of bile aspiration in the airway tract of CF individuals. Aspirated bile is associated with the severity of lung diseases and chronic inflammation caused by Pseudomonas aeruginosa as the most common pathogen of CF respiratory tract infections. P. aeruginosa is equipped with several mechanisms to facilitate the infection process, including but not limited to the expression of virulence factors, biofilm formation, and antimicrobial resistance, all of which are under the strong regulation of quorum sensing (QS) mechanism. By increasing the expression of lasI, rhlI, and pqsA-E, bile exposure directly impacts the QS network. An increase in psl expression and pyocyanin production can promote biofilm formation. Along with the loss of flagella and reduced swarming motility, GER-derived bile can repress the expression of genes involved in creating an acute infection, such as expression of Type Three Secretion (T3SS), hydrogen cyanide (hcnABC), amidase (amiR), and phenazine (phzA-E). Inversely, to cause persistent infection, bile exposure can increase the Type Six Secretion System (T6SS) and efflux pump expression, which can trigger resistance to antibiotics such as colistin, polymyxin B, and erythromycin. This review will discuss the influence of aspirated bile on the pathogenesis, resistance, and persistence of P. aeruginosa in CF patients.

The Anti-Oxidant Curcumin Solubilized as Oil-in-Water Nanoemulsions or Chitosan Nanocapsules Effectively Reduces Helicobacter pylori Growth, Bacterial Biofilm Formation, Gastric Cell Adhesion and Internalization

The bacterium Helicobacter pylori (H. pylori) represents a major risk factor associated with the development of gastric cancer. The anti-oxidant curcumin has been ascribed many benefits to human health, including bactericidal effects. However, these effects are poorly reproducible because the molecule is extremely unstable and water insoluble. Here we solubilized curcumin as either nanoemulsions or chitosan nanocapsules and tested the effects on H. pylori. The nanoemulsions were on average 200 nm in diameter with a PdI ≤ 0.16 and a negative zeta potential (-54 mV), while the nanocapsules were 305 nm in diameter with a PdI ≤ 0.29 and a positive zeta potential (+68 mV). Nanocapsules were safer than nanoemulsions when testing effects on the viability of GES-1 gastric cells. Also, nanocapsules were more efficient than nanoemulsions at inhibiting H. pylori growth (minimal inhibitory concentration: 50 and 75 μM, respectively), whereby chitosan contributed to this activity. Importantly, both formulations effectively diminished H. pylori's adherence to and internalization by GES-1 cells, as well as biofilm formation. In summary, the demonstrated activity of the curcumin nanoformulations described here against H. pylori posit them as having great potential to treat or complement other therapies currently in use against H. pylori infection.

Review: The Chemistry, Toxicity and Antibacterial Activity of Curcumin and Its Analogues

Antimicrobial resistance is a global challenge that is already exacting a heavy price both in terms of human health and financial cost. Novel ways of approaching this crisis include the investigation of natural products. Curcumin is the major constituent in turmeric, and it is commonly used in the preparation of Asian cuisine. In addition, it possesses a wide range of pharmacological properties. This review provides a detailed account of curcumin and its analogues' antibacterial activity against both gram-positive and gram-negative isolates, including its potential mechanism(s) of action and the safety and toxicity in human and animal models. We also highlight the key challenges in terms of solubility/bioavailability associated with the use of curcumin and include research on how these challenges have been overcome.

Biofilm formation of Pseudomonas aeruginosa in spaceflight is minimized on lubricant impregnated surfaces

The undesirable, yet inevitable, presence of bacterial biofilms in spacecraft poses a risk to the proper functioning of systems and to astronauts' health. To mitigate the risks that arise from them, it is important to understand biofilms' behavior in microgravity. As part of the Space Biofilms project, biofilms of Pseudomonas aeruginosa were grown in spaceflight over material surfaces. Stainless Steel 316 (SS316) and passivated SS316 were tested for their relevance as spaceflight hardware components, while a lubricant impregnated surface (LIS) was tested as potential biofilm control strategy. The morphology and gene expression of biofilms were characterized. Biofilms in microgravity are less robust than on Earth. LIS strongly inhibits biofilm formation compared to SS. Furthermore, this effect is even greater in spaceflight than on Earth, making LIS a promising option for spacecraft use. Transcriptomic profiles for the different conditions are presented, and potential mechanisms of biofilm reduction on LIS are discussed.

Biofilm stimulating activity of solanidine and Solasodine in Pseudomonas aeruginosa

BACKGROUND

Biofilm formation has reported as an important virulence associated properties of Pseudomonas aeruginosa that is regulated by quorum-sensing associated genes. Biofilm and quorum-sensing interfering properties of steroidal alkaloids, Solanidine and Solasodine were investigated in the present study.

RESULTS

Biofilm formation capacity and relative expression level of five studied genes(lasI, lasR, rhlI, rhlR and algD) were significantly increased dose-dependently after treatment with sub-inhibitory concentrations (32 and 512 µg/ml) of the both Solanidine and Solasodine. Biofilm formation capacity was more stimulated in weak biofilm formers(9 iaolates) in comparison to the strong biofilm producers(11 isolates). The lasI gene was the most induced QS-associated gene among five investigated genes.

CONCLUSION

Biofilm inducing properties of the plants alkaloids and probably medicines derived from them has to be considered for revision of therapeutic guidelines. Investigating the biofilm stimulating properties of corticosteroids and other medicines that comes from plant alkaloids also strongly proposed.

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.

Genetic and environmental determinants of surface adaptations in Pseudomonas aeruginosa

Pseudomonas aeruginosa is a well-studied Gram-negative opportunistic bacterium that thrives in markedly varied environments. It is a nutritionally versatile microbe that can colonize a host as well as exist in the environment. Unicellular, planktonic cells of P. aeruginosa can come together to perform a coordinated swarming movement or turn into a sessile, surface-adhered population called biofilm. These collective behaviours produce strikingly different outcomes. While swarming motility rapidly disseminates the bacterial population, biofilm collectively protects the population from environmental stresses such as heat, drought, toxic chemicals, grazing by predators, and attack by host immune cells and antibiotics. The ubiquitous nature of P. aeruginosa is likely to be supported by the timely transition between planktonic, swarming and biofilm lifestyles. The social behaviours of this bacteria viz biofilm and swarm modes are controlled by signals from quorum-sensing networks, LasI-LasR, RhlI-RhlR and PQS-MvfR, and several other sensory kinases and response regulators. A combination of environmental and genetic cues regulates the transition of the P. aeruginosa population to specific states. The current review is aimed at discussing key factors that promote physiologically distinct transitioning of the P. aeruginosa population.

In vitro and in vivo antibiofilm activity of the synthetic antimicrobial peptide WLBU2 against multiple drug resistant Pseudomonas aeruginosa strains

BACKGROUND

The global crisis of antibiotic resistance increases the demand for the novel promising alternative drugs such as antimicrobial peptides (AMPs). Here, the antibiofilm activity of the WLBU2 peptide against Pseudomonas aeruginosa (P. aeruginosa) isolates was investigated in this study.

METHODS

Two clinical MDR and carbapenem resistant P. aeruginosa (CRPA) isolates, and standard P. aeruginosa ATCC 27,853 were investigated. The MIC and MBC of WLBU2 were determined. The MBIC was determined to evaluate inhibitory activity of WLBU2 on biofilm formation and MBEC to dispersal activity on preformed biofilm. The relative expression levels of biofilm-associated genes including rhlI, rhlR, lasI and lasR were analyzed using RT-qPCR. In vivo evaluation of inhibitory effect of WLBU2 on biofilm formation was performed in the murine models of P. aeruginosa biofilm-associated subcutaneous catheter infection.

RESULTS

MIC and MBC of WLBU2 for both MDR and ATCC 27,853 P. aeruginosa strains were 8 and 16 µg/mL, respectively, while both the MIC and MBC against the CR strain were 4 µg/mL. MBIC was estimated to be 64 µg/ml for all strains. MBEC against MDR and ATCC 27,853- P. aeruginosa strains was 128 µg/ml and against CRPA was 64 µg/ml. The bacterial adhesion to a static abiotic solid surface (the surface in the polypropylene microtiter wells) was significantly inhibited at 1/4× MIC in all P. aeruginosa strains and at 1/8× MIC in CRPA strain (P < 0.05). Following treatment with WLBU2 at 1/8× MIC, significant inhibition in biofilm formation was observed in all isolates (P < 0.05). Results of the colorimetric assay showed that WLBU2 at 4× MIC was able to disperse 69.7% and 81.3% of pre-formed biofilms on abiotic surface produced by MDR and standard (ATCC 27,853) P. aeruginosa, respectively (P < 0.03), while a 92.2% reduction in the CRPA biofilm was observed after treatment with 4× MIC WLBU2 (P < 0.03). The expression levels of all genes in isolates treated with 1/2 MIC of WLBU2 were down-regulated by more than four-fold compared to the untreated isolates (P < 0.05). WLBU2 significantly inhibited biofilm formation in murine catheter-associated CRPA infection model at 1/4×MIC, 1/2×MIC, and 1×MIC by 33%, 52%, and 67%, respectively.

CONCLUSION

Considering relatively strong inhibitory and eradication potency of WLBU2 on the P. aeruginosa biofilms in in vitro and in vivo conditions, the peptide can be considered as a promising candidate for designing an antibiofilm drug.

Immune escape strategies of Pseudomonas aeruginosa to establish chronic infection

The infection caused by P. aeruginosa still is dangerous throughout the world. This is partly due to its immune escape mechanisms considerably increasing the bacterial survival in the host. By escape from recognition by TLRs, interference with complement system activation, phagocytosis inhibition, production of ROS, inhibition of NET production, interference with the generation of cytokines, inflammasome inhibition, reduced antigen presentation, interference with cellular and humoral immunity, and induction of apoptotic cell death and MDSc, P. aeruginosa breaks down the barriers of the immune system and causes lethal infections in the host. Recognition of other immune escape mechanisms of P. aeruginosa may provide a basis for the future treatment of the infection. This manuscript may provide new insights and information for the development of new strategies to combat P. aeruginosa infection. In the present manuscript, the escape mechanisms of P. aeruginosa against immune response would be reviewed.

Pseudomonas Aeruginosa Theft Biofilm Require Host Lipids of Cutaneous Wound

OBJECTIVE

This work addressing complexities in wound infection, seeks to test the reliance of bacterial pathogen Pseudomonas aeruginosa (PA) on host skin lipids to form biofilm with pathological consequences.

BACKGROUND

PA biofilm causes wound chronicity. Both CDC as well as NIH recognizes biofilm infection as a threat leading to wound chronicity. Chronic wounds on lower extremities often lead to surgical limb amputation.

METHODS

An established preclinical porcine chronic wound biofilm model, infected with PA or Pseudomonas aeruginosa ceramidase mutant (PA ∆Cer ), was used.

RESULTS

We observed that bacteria drew resource from host lipids to induce PA ceramidase expression by three orders of magnitude. PA utilized product of host ceramide catabolism to augment transcription of PA ceramidase. Biofilm formation was more robust in PA compared to PA ∆Cer . Downstream products of such metabolism such as sphingosine and sphingosine-1-phosphate were both directly implicated in the induction of ceramidase and inhibition of peroxisome proliferator-activated receptor (PPAR)δ, respectively. PA biofilm, in a ceram-idastin-sensitive manner, also silenced PPARδ via induction of miR-106b. Low PPARδ limited ABCA12 expression resulting in disruption of skin lipid homeostasis. Barrier function of the wound-site was thus compromised.

CONCLUSIONS

This work demonstrates that microbial pathogens must co-opt host skin lipids to unleash biofilm pathogenicity. Anti-biofilm strategies must not necessarily always target the microbe and targeting host lipids at risk of infection could be productive. This work may be viewed as a first step, laying fundamental mechanistic groundwork, toward a paradigm change in biofilm management.

Vibrio parahaemolyticus and Vibrio vulnificus in vitro colonization on plastics influenced by temperature and strain variability

Marine bacteria often exist in biofilms as communities attached to surfaces, like plastic. Growing concerns exist regarding marine plastics acting as potential vectors of pathogenic Vibrio, especially in a changing climate. It has been generalized that Vibrio vulnificus and Vibrio parahaemolyticus often attach to plastic surfaces. Different strains of these Vibrios exist having different growth and biofilm-forming properties. This study evaluated how temperature and strain variability affect V. parahaemolyticus and V. vulnificus biofilm formation and characteristics on glass (GL), low-density polyethylene (LDPE), polypropylene (PP), and polystyrene (PS). All strains of both species attached to GL and all plastics at 25, 30, and 35°C. As a species, V. vulnificus produced more biofilm on PS (p ≤ 0.05) compared to GL, and biofilm biomass was enhanced at 25°C compared to 30° (p ≤ 0.01) and 35°C (p ≤ 0.01). However, all individual strains' biofilm biomass and cell densities varied greatly at all temperatures tested. Comparisons of biofilm-forming strains for each species revealed a positive correlation (r = 0.58) between their dry biomass weight and OD₅₇₀ values from crystal violet staining, and total dry biofilm biomass for both species was greater (p ≤ 0.01) on plastics compared to GL. It was also found that extracellular polymeric substance (EPS) chemical characteristics were similar on all plastics of both species, with extracellular proteins mainly contributing to the composition of EPS. All strains were hydrophobic at 25, 30, and 35°C, further illustrating both species' affinity for potential attachment to plastics. Taken together, this study suggests that different strains of V. parahaemolyticus and V. vulnificus can rapidly form biofilms with high cell densities on different plastic types in vitro. However, the biofilm process is highly variable and is species-, strain-specific, and dependent on plastic type, especially under different temperatures.

The Anti-Biofilm Activity and Mechanism of Apigenin-7-O-Glucoside Against Staphylococcus aureus and Escherichia coli

Introduction

This study aimed to examine the anti-biofilm activity and mechanism of gallic acid (GA), kaempferol-7-O-glucoside (K7G) and apigenin-7-O-glucoside (A7G) against Staphylococcus aureus and Escherichia coli.

Methods

The antibacterial activity of the natural compounds was determined by serial dilution method. The inhibitory activity of natural compounds on biofilms was determined by crystal violet staining method. The effects and mechanisms of natural compounds on bacterial biofilms were analyzed by atomic force microscopy.

Results

In our study, compared with GA and K7G, A7G was found to exhibit the strongest anti-biofilm and antibacterial activities. The minimum biofilm inhibitory concentration (MBIC) of A7G against S. aureus and E. coli was 0.20 mg/mL and 0.10 mg/mL, respectively. The inhibition rates of 1/2 MIC of A7G on biofilms of S. aureus and E. coli were 88.9%, and 83.2% respectively. Moreover, atomic force microscope (AFM) images showed the three-dimensional biofilm morphology of S. aureus and E. coli, and the results indicated that A7G was highly effective in biofilm inhibition.

Discussion

It was found that the inhibition of A7G on biofilm was achieved through inhibiting on exopolysaccharides (EPS), quorum sensing (QS), and cell surface hydrophobicity (CSH). A7G exerted strong anti-biofilm activities by inhibiting EPS production, QS, and CSH. Hence, A7G, as a natural substance, could be a promising novel antibacterial and anti-biofilm agent for control of biofilm in food industry.

Pseudomonas virulence factor controls expression of virulence genes in Pseudomonas entomophila

Quorum sensing is a communication strategy that bacteria use to collectively alter gene expression in response to cell density. Pathogens use quorum sensing systems to control activities vital to infection, such as the production of virulence factors and biofilm formation. The Pseudomonas virulence factor (pvf) gene cluster encodes a signaling system (Pvf) that is present in over 500 strains of proteobacteria, including strains that infect a variety of plant and human hosts. We have shown that Pvf regulates the production of secreted proteins and small molecules in the insect pathogen Pseudomonas entomophila L48. Here, we identified genes that are likely regulated by Pvf using the model strain P. entomophila L48 which does not contain other known quorum sensing systems. Pvf regulated genes were identified through comparing the transcriptomes of wildtype P. entomophila and a pvf deletion mutant (ΔpvfA-D). We found that deletion of pvfA-D affected the expression of approximately 300 genes involved in virulence, the type VI secretion system, siderophore transport, and branched chain amino acid biosynthesis. Additionally, we identified seven putative biosynthetic gene clusters with reduced expression in ΔpvfA-D. Our results indicate that Pvf controls multiple virulence mechanisms in P. entomophila L48. Characterizing genes regulated by Pvf will aid understanding of host-pathogen interactions and development of anti-virulence strategies against P. entomophila and other pvf-containing strains.

Anti-Quorum-Sensing Potential of Ethanolic Extracts of Aromatic Plants from the Flora of Cyprus

Quorum sensing (QS) is a form of intra- and inter-species communication system employed by bacteria to regulate their collective behavior in a cell population-dependent manner. QS has been implicated in the virulence of several pathogenic bacteria. This work aimed to investigate the anti-QS potential of ethanolic extracts of eight aromatic plants of Cyprus, namely, Origanum vulgare subsp. hirtum, Rosmarinus officinalis, Salvia officinalis, Lavendula spp., Calendula officinalis, Melissa officinalis, Sideritis cypria, and Aloysia citriodora. We initially assessed the effects of the extracts on autoinducer 2 (AI-2) signaling activity, using Vibrio harveyi BB170 as a reported strain. We subsequently assessed the effect of the ethanolic extracts on QS-related processes, including biofilm formation and the swarming and swimming motilities of Escherichia coli MG1655. Of the tested ethanolic extracts, those of Origanum vulgare subsp. hirtum, Rosmarinus officinalis, and Salvia officinalis were the most potent AI-2 signaling inhibitors, while the extracts from the other plants exhibited low to moderate inhibitory activity. These three ethanolic extracts also inhibited the biofilm formation (>60%) of E. coli MG1655, as well as its swimming and swarming motilities, in a concentration-dependent manner. These extracts may be considered true anti-QS inhibitors because they disrupt QS-related activities of E. coli MG1655 without affecting bacterial growth. The results suggest that plants from the unexplored flora of Cyprus could serve as a source for identifying novel anti-QS inhibitors to treat infectious diseases caused by pathogens that are resistant to antibiotics.

Targeting the Holy Triangle of Quorum Sensing, Biofilm Formation, and Antibiotic Resistance in Pathogenic Bacteria

Chronic and recurrent bacterial infections are frequently associated with the formation of biofilms on biotic or abiotic materials that are composed of mono- or multi-species cultures of bacteria/fungi embedded in an extracellular matrix produced by the microorganisms. Biofilm formation is, among others, regulated by quorum sensing (QS) which is an interbacterial communication system usually composed of two-component systems (TCSs) of secreted autoinducer compounds that activate signal transduction pathways through interaction with their respective receptors. Embedded in the biofilms, the bacteria are protected from environmental stress stimuli, and they often show reduced responses to antibiotics, making it difficult to eradicate the bacterial infection. Besides reduced penetration of antibiotics through the intricate structure of the biofilms, the sessile biofilm-embedded bacteria show reduced metabolic activity making them intrinsically less sensitive to antibiotics. Moreover, they frequently express elevated levels of efflux pumps that extrude antibiotics, thereby reducing their intracellular levels. Some efflux pumps are involved in the secretion of QS compounds and biofilm-related materials, besides being important for removing toxic substances from the bacteria. Some efflux pump inhibitors (EPIs) have been shown to both prevent biofilm formation and sensitize the bacteria to antibiotics, suggesting a relationship between these processes. Additionally, QS inhibitors or quenchers may affect antibiotic susceptibility. Thus, targeting elements that regulate QS and biofilm formation might be a promising approach to combat antibiotic-resistant biofilm-related bacterial infections.

Zeolite 4A as a jammer of bacterial communication in Chromobacterium violaceum and Pseudomonas aeruginosa

Aim: To investigate the hypothesis that zeolites interfere with quorum-sensing (QS) systems of Chromobacterium violaceum and Pseudomonas aeruginosa by adsorbing N-acyl homoserine lactone (AHL) signal molecules. Methods: QS inhibition by zeolite 4A was investigated using an AHL-based bioreporter assay. The adsorption of the AHLs was evaluated by performing inductively coupled plasma-optical emission spectroscopy and confirmed by Monte Carlo and molecular dynamic simulations. Results: Zeolite 4A reduced the violacein production in C. violaceum by over 90% and the biofilm formation, elastase and pyocyanin production in P. aeruginosa by 87, 68 and 98%, respectively. Conclusion: Zeolite 4A disrupts the QS systems of C. violaceum and P. aeruginosa by means of adsorbing 3-oxo-C6-AHL and 3-oxo-C12-AHL signaling molecules and can be developed as a novel QS jammer to combat P. aeruginosa-related infections.

A biophysical threshold for biofilm formation

Bacteria are ubiquitous in our daily lives, either as motile planktonic cells or as immobilized surface-attached biofilms. These different phenotypic states play key roles in agriculture, environment, industry, and medicine; hence, it is critically important to be able to predict the conditions under which bacteria transition from one state to the other. Unfortunately, these transitions depend on a dizzyingly complex array of factors that are determined by the intrinsic properties of the individual cells as well as those of their surrounding environments, and are thus challenging to describe. To address this issue, here, we develop a generally-applicable biophysical model of the interplay between motility-mediated dispersal and biofilm formation under positive quorum sensing control. Using this model, we establish a universal rule predicting how the onset and extent of biofilm formation depend collectively on cell concentration and motility, nutrient diffusion and consumption, chemotactic sensing, and autoinducer production. Our work thus provides a key step toward quantitatively predicting and controlling biofilm formation in diverse and complex settings.

Impact of Quorum Sensing System on Virulence Factors Production in Pseudomonas aeruginosa

Pseudomonas aeruginosa is an important pathogen that is frequently associated with nosocomial infections. The goal of this work was to determine the relationship between the quorum sensing system (QS) and the production of virulence factors in P. aeruginosa. A number of 100 P. aeruginosa isolates were collected from various clinical sources from different Mansoura university hospitals in the period from April 2018 till April 2019. PCR screening of QS genes in the isolates was carried out including lasI, lasR, rhlI and rhlR. Thereafter, assay of the production of different virulence factors in the isolates was established including biofilm formation, pyocyanin production, protease production, lipase production, hemolysin production as well as swimming motility. Finally, statistical analysis of the data was performed to confirm the relationship between the QS and the production of virulence factors. Out of the 100 P. aeruginosa isolates, 27 clinical isolates were QS deficient. PCR analysis revealed that 8 isolates lacked lasR gene, 15 isolates lacked lasR and rhlR genes, 1 isolate lacked lasR and lasI genes, 2 isolates lacked lasR, lasI and rhlR genes and 1 isolate lacked rhlR, rhlI and lasR genes. There was a significant decrease observed in the production of pyocyanin, protease, lipase, hemolysin and biofilm formation as well as swimming motility in P. aeruginosa QS deficient isolates in comparison to non-QS deficient ones. There was a clear association between QS and virulence factors production in P. aeruginosa. This could open the door for novel promising targets for developing new therapeutic strategies against infections caused by this pathogen.

Phytochemical Analysis, Antioxidant, Antimicrobial, and Anti-Swarming Properties of Hibiscus sabdariffa L. Calyx Extracts: In Vitro and In Silico Modelling Approaches

The aim of this study was to investigate the phytochemical composition of dried Roselle calyx (Hibiscus sabdariffa L.) using both ethanolic and aqueous extracts. We report the antimicrobial activities against a wide range of bacteria, yeast, and fungi. The antioxidant activities were tested using 2,2-diphenyl-1-picrylhydrazyl (DPPH), hydroxyl, and 2–2′-azinobis-(3-ethylbenzthiazoline-6-sulfonic acid) radical scavenging assays. We report also for the first time the effect of the swarming motility in Pseudomonas aeruginosa PAO1. Our results showed that the tested two extracts were a rich source of phenols, flavonoids, and tannins with different degrees. Additionally, eleven phytoconstituents were identified by LC/MS technique (Hibiscus acid: 3-caffeoylquinic acid, 5-caffeoylquinic acid, 5-feruloylquinic acid, cyanidin 3-o-glucoside, myricetin, quercetin 7-o-rutinoside, quercetin 3-o-glucoside, delphinidin 3-o-sambubioside, and kaempferol 3-o-p-coumaroyl-glucoside). Also, it was shown that the calyx extract can scavenge 86% of the DPPH radical, while the rate of 53% and 23% of inhibition of the DPPH was obtained only at the concentration of 125 and 50 µg/mL, and a small inhibition was made at a concentration of 5 μg/mL. Roselle extracts inhibited the growth of the selected microorganisms at low concentrations, while higher concentrations are needed to completely kill them. However, no activity against CVB-3 was recorded for both extracts. In addition, the obtained extracts reduced the swarming motility of P. aeruginosa at 2.5 mg/ml. The docking simulation showed acceptable binding affinities (up to −9.6 kcal/mol) and interaction with key residues of 1JIJ, 2QZW, and 2UVO. The obtained results highlighted the potential use of Roselle extract as a source of phytoconstituents with promising antimicrobial, antioxidant, and anti-quorum sensing activities.

Biodiversity of N-acyl homoserine lactonase (aiiA) gene from Bacillus subtilis

Microorganisms rely on the benefit of using chemical signals called autoinducers (AIs) as a connection matter in term of population, this mechanism is known as quorum sensing (QS). Quorum sensing is responsible for formation of biofilm together with virulence in bacteria. The most known QS molecule is N-acyl homoserine lactones (AHLs). A lot of degrading enzymes including lactonases that open the AHL ring and acylases that breakdown its acyl side chain can degrade or inactivate AHL. Due to similarity in lactone ring structure among AHLs it is susceptible to most of lactonases. Bacillus species are among the most promising bacteria producing AHL-lactonase. The aim of the work is to identify and study the diversity of the AHL-Lactonase gene among different Bacillus subtilis as a promising Quorum Quenching (QQ) strategy to prevent bacterial infections and biofilm formation. The AHL-lactonase (aiiA) gene of 64 B. subtilis isolates was amplified and sequenced followed by multiple sequence alignment of the translated amino acid sequences, homology modeling and docking study. An expected PCR product of about 750 base pair was detected in 22 B. subtilis isolates, and the results revealed that the isolates' sequences showed identity ranged between 97.61% to 99.47% with those in the NCBI GenBank database with 100% query coverage and 0.0 E-value. In addition, the results revealed high level of identity between many aiiA gene sequences of our isolates as they were closely related to the same sequences to many sequences of the NCBI GenBank database. The alignment of the amino acid sequences from the 22 B. subtilis isolates indicated that 84.4% of the amino acid residues were conserved between the aligned sequences. Docking of the co-crystalized ligand to wildtype and H109Y mutated protein showed a significant reduction of docking score for the mutated protein. This result indicate that this mutation might affect recognition or at least kinetics of these enzymes and hence their roles in quorum-quenching.

Phage Infection Restores PQS Signaling and Enhances Growth of a Pseudomonas aeruginosa lasI Quorum-Sensing Mutant

Chemical communication between bacteria and between bacteria and the bacteriophage (phage) viruses that prey on them can shape the outcomes of phage-bacterial encounters. Quorum sensing (QS) is a bacterial cell-to-cell communication process that promotes collective undertaking of group behaviors. QS relies on the production, release, accumulation, and detection of signal molecules called autoinducers. Phages can exploit QS-mediated communication to manipulate their hosts and maximize their own survival. In the opportunistic pathogen Pseudomonas aeruginosa, the LasI/R QS system induces the RhlI/R QS system, and in opposing manners, these two systems control the QS system that relies on the autoinducer called PQS. A P. aeruginosa ΔlasI mutant is impaired in PQS synthesis, leading to accumulation of the precursor molecule HHQ, and HHQ suppresses growth of the P. aeruginosa ΔlasI strain. We show that, in response to a phage infection, the P. aeruginosa ΔlasI mutant reactivates QS, which, in turn, restores pqsH expression, enabling conversion of HHQ into PQS. Moreover, downstream QS target genes encoding virulence factors are induced. Additionally, phage-infected P. aeruginosa ΔlasI cells transiently exhibit superior growth compared to uninfected cells.

IMPORTANCE Clinical isolates of P. aeruginosa frequently harbor mutations in particular QS genes. Here, we show that infection by select temperate phages restores QS, a cell-to-cell communication mechanism in a P. aeruginosa QS mutant. Restoration of QS increases expression of genes encoding virulence factors. Thus, phage infection of select P. aeruginosa strains may increase bacterial pathogenicity, underscoring the importance of characterizing phage-host interactions in the context of bacterial mutants that are relevant in clinical settings.

Identification of Protein Drug Targets of Biofilm Formation and Quorum Sensing in Multidrug Resistant Enterococcus faecalis

Abstract:

Enterococcus faecalis (E. faecalis) is an opportunistic multidrug-resistant (MDR) pathogen found in the guts of humans and farmed animals. Due to the occurrence of (MDR) strain there is an urgent need to look for an alternative treatment approach. E. faecalis is a Gram-positive bacterium, which is among the most prevalent multidrug resistant hospital pathogens. Its ability to develop quorum sensing (QS) mediated biofilm formation further exacerbates the pathogenicity and triggers lifethreatening infections. Therefore, developing a suitable remedy for curing E. faecalis mediated enterococcal infections is an arduous task. Several putative virulence factors and proteins are involved in the development of biofilms in E. faecalis. Such proteins often play important roles in virulence, disease, and colonization by pathogens. The elucidation of the structure-function relationship of such protein drug targets and the interacting compounds could provide an attractive paradigm towards developing structure-based drugs against E. faecalis. This review provides a comprehensive overview of the current status, enigmas that warrant further studies, and the prospects toward alleviating the antibiotic resistance in E. faecalis. Specifically, the role of biofilm and quorum sensing (QS) in the emergence of MDR strains had been elaborated along with the importance of the protein drug targets involved in both the processes.

Diversity of bet-hedging strategies in microbial communities-Recent cases and insights

Microbial communities are continuously exposed to unpredictable changes in their environment. To thrive in such dynamic habitats, microorganisms have developed the ability to readily switch phenotypes, resulting in a number of differently adapted subpopulations expressing various traits. In evolutionary biology, a particular case of phenotypic heterogeneity that evolved in an unpredictably changing environment has been defined as bet‐hedging. Bet‐hedging is a risk‐spreading strategy where isogenic populations stochastically (randomly) diversify their phenotypes, often resulting in maladapted individuals that suffer lower reproductive success. This fitness trade‐off in a specific environment may have a selective advantage upon the sudden environmental shift. Thus, a bet‐hedging strategy allows populations to persist in very dynamic habitats, but with a particular fitness cost. In recent years, numerous examples of phenotypic heterogeneity in different microorganisms have been observed, some suggesting bet‐hedging. Here, we highlight the latest reports concerning bet‐hedging phenomena in various microorganisms to show how versatile this strategy is within the microbial realms.

This article is categorized under:

Infectious Diseases > Molecular and Cellular Physiology

Inhibition of the Quorum Sensing System, Elastase Production and Biofilm Formation in Pseudomonas aeruginosa by Psammaplin A and Bisaprasin

Natural products derived from marine sponges have exhibited bioactivity and, in some cases, serve as potent quorum sensing inhibitory agents that prevent biofilm formation and attenuate virulence factor expression by pathogenic microorganisms. In this study, the inhibitory activity of the psammaplin-type compounds, psammaplin A (1) and bisaprasin (2), isolated from the marine sponge, Aplysinellarhax, are evaluated in quorum sensing inhibitory assays based on the Pseudomonas aeruginosa PAO1 lasB-gfp(ASV) and rhlA-gfp(ASV) biosensor strains. The results indicate that psammaplin A (1) showed moderate inhibition on lasB-gfp expression, but significantly inhibited the QS-gene promoter, rhlA-gfp, with IC50 values at 14.02 μM and 4.99 μM, respectively. In contrast, bisaprasin (2) displayed significant florescence inhibition in both biosensors, PAO1 lasB-gfp and rhlA-gfp, with IC50 values at 3.53 μM and 2.41 μM, respectively. Preliminary analysis suggested the importance of the bromotyrosine and oxime functionalities for QSI activity in these molecules. In addition, psammaplin A and bisaprasin downregulated elastase expression as determined by the standard enzymatic elastase assay, although greater reduction in elastase production was observed with 1 at 50 μM and 100 μM. Furthermore, the study revealed that bisaprasin (2) reduced biofilm formation in P. aeruginosa.

Exploitation of the Antibacterial Properties of Photoactivated Curcumin as ‘Green’ Tool for Food Preservation

In the search for non-chemical and green methods to counteract the bacterial contamination of foods, the use of natural substances with antimicrobial properties and light irradiation at proper light waves has been extensively investigated. In particular, the combination of both techniques, called photodynamic inactivation (PDI), is based on the fact that some natural substances act as photosensitizers, i.e., produce bioactive effects under irradiation. Notably, curcumin is a potent natural antibacterial and effective photosensitizer that is able to induce photodynamic activation in the visible light range (specifically for blue light). Some practical applications have been investigated with particular reference to food preservation from bacterial contaminants.

Antibacterial and antibiofilm activity of Peganum harmala seed extract against multidrug-resistant Pseudomonas aeruginosa pathogenic isolates and molecular mechanism of action

Biofilm formation of the opportunistic pathogen Pseudomonas (P). aeruginosa is one of the major global challenges to control nosocomial infections due to their high resistance to antimicrobials and host defense mechanisms. The present study aimed to assess the antibacterial and the antibiofilm activities of Peganum (P). harmala seed extract against multidrug-resistant P. aeruginosa isolates. Chemical identification of the active compound and determination of its molecular mechanism of action were also investigated. Results showed that P. harmala n-butanol "n-BuOH" extract exhibited antibacterial activity against multidrug-resistant P. aeruginosa isolates. This extract was even more active than conventional antibiotics cefazolin and vaamox when tested against three P. aeruginosa multidrug-resistant isolates. In addition, P. harmala n-BuOH extract exhibited potent bactericidal activity against PAO1 strain at MIC value corresponding to 500 µg/mL and attained 100% killing effect at 24 h of incubation. Furthermore, P. harmala n-BuOH extract showed an antibiofilm activity against P. aeruginosa PAO1 and exhibited 80.43% inhibition at sub-inhibitory concentration. The extract also eradicated 83.99% of the biofilm-forming bacteria. The active compound was identified by gas chromatography-mass spectrometry as an indole alkaloid harmaline. Transcriptomic analysis showed complete inhibition of the biofilm-related gene pilA when PAO1 cells were treated with harmaline. Our results revealed that P. harmala seed extract and its active compound harmaline could be considered as a candidate for a new treatment of multidrug-resistant P. aeruginosa pathogens-associated biofilm infections.

Effects of active compounds from Cassia fistula on quorum sensing mediated virulence and biofilm formation in Pseudomonas aeruginosa

Pseudomonas aeruginosa infections are attributed to its ability to form biofilms and are difficult to eliminate with antibiotic treatment.

Identification of small molecules that strongly inhibit bacterial quorum sensing using a high-throughput lipid vesicle lysis assay

Strategies to both monitor and block bacterial quorum sensing (QS), and thus associated infections, are of significant interest. We developed a straightforward assay to monitor biosurfactants and lytic agents produced by bacteria under the control of QS. The method is based on the lysis of synthetic lipid vesicles containing the environmentally sensitive fluorescent dye calcein. This assay allows for the in situ screening of compounds capable of altering biosurfactant production by bacteria, and thereby the identification of molecules that could potentially modulate QS pathways, and avoids the constraints of many of the cell-based assays in use today. Application of this assay in a high-throughput format revealed five molecules capable of blocking vesicle lysis by S. aureus. Two of these compounds were found to almost completely inhibit agr-based QS in S. aureus and represent the most potent small-molecule-derived QS inhibitors reported in this formidable pathogen.

Repurposing phytochemicals as anti-virulent agents to attenuate quorum sensing-regulated virulence factors and biofilm formation in Pseudomonas aeruginosa

Unregulated consumption and overexploitation of antibiotics have paved the way for emergence of antibiotic‐resistant strains and ‘superbugs’. Pseudomonas aeruginosa is among the opportunistic nosocomial pathogens causing devastating infections in clinical set‐ups globally. Its artillery equipped with diversified virulence elements, extensive antibiotic resistance and biofilms has made it a ‘hard‐to‐treat’ pathogen. The pathogenicity of P. aeruginosa is modulated by an intricate cell density‐dependent mechanism called quorum sensing (QS). The virulence artillery of P. aeruginosa is firmly controlled by QS genes, and their expression drives the aggressiveness of the infection. Attempts to identify and develop novel antimicrobials have seen a sharp rise in the past decade. Among different proposed mechanisms, a novel anti‐virulence approach to target pseudomonal infections by virtue of anti‐QS and anti‐biofilm drugs appears to occupy the centre stage. In this respect, bioactive phytochemicals have gained prominence among the scientific community owing to their significant quorum quenching (QQ) properties. Recent studies have shed light on the QQ activities of various phytochemicals and other drugs in perturbing the QS‐dependent virulence in P. aeruginosa. This review highlights the recent evidences that reinforce the application of plant bioactives for combating pseudomonal infections, their advantages and shortcomings in anti‐virulence therapy.

Genomic and Metabolic Characteristics of the Pathogenicity in Pseudomonas aeruginosa

In recent years, the effectiveness of antimicrobials in the treatment of Pseudomonas aeruginosa infections has gradually decreased. This pathogen can be observed in several clinical cases, such as pneumonia, urinary tract infections, sepsis, in immunocompromised hosts, such as neutropenic cancer, burns, and AIDS patients. Furthermore, Pseudomonas aeruginosa causes diseases in both livestock and pets. The highly flexible and versatile genome of P. aeruginosa allows it to have a high rate of pathogenicity. The numerous secreted virulence factors, resulting from its numerous secretion systems, the multi-resistance to different classes of antibiotics, and the ability to produce biofilms are pathogenicity factors that cause numerous problems in the fight against P. aeruginosa infections and that must be better understood for an effective treatment. Infections by P. aeruginosa represent, therefore, a major health problem and, as resistance genes can be disseminated between the microbiotas associated with humans, animals, and the environment, this issue needs be addressed on the basis of an One Health approach. This review intends to bring together and describe in detail the molecular and metabolic pathways in P. aeruginosa's pathogenesis, to contribute for the development of a more targeted therapy against this pathogen.

Quorum-sensing regulation of virulence factors in bacterial biofilm

Chronic polymicrobial wound infections are often characterized by the presence of bacterial biofilms. They show considerable structural and functional heterogeneity, which influences the choice of antimicrobial therapy and wound healing dynamics. The hallmarks of biofilm-associated bacterial infections include elevated antibiotic resistance and extreme pathogenicity. Biofilm helps bacteria to evade the host defense mechanisms and persist longer in the host. Quorum-sensing (QS)-mediated cell signaling primarily regulates biofilm formation in chronic infections and plays a major role in eliciting virulence. This review focuses on the QS mechanisms of two major bacterial pathogens, Staphylococcus aureus and Pseudomonas aeruginosa and explains how they interact in the wound microenvironment to regulate biofilm development and virulence. The review also provides an insight into the treatment modalities aimed at eradicating polymicrobial biofilms. This information will help us develop better diagnostic modalities and devise effective treatment regimens to successfully manage and overcome severe life-threatening bacterial infections.

Polymicrobial Interactions in the Cystic Fibrosis Airway Microbiome Impact the Antimicrobial Susceptibility of Pseudomonas aeruginosa

Pseudomonas aeruginosa is one of the most dominant pathogens in cystic fibrosis (CF) airway disease and contributes to significant inflammation, airway damage, and poorer disease outcomes. The CF airway is now known to be host to a complex community of microorganisms, and polymicrobial interactions have been shown to play an important role in shaping P. aeruginosa pathogenicity and resistance. P. aeruginosa can cause chronic infections that once established are almost impossible to eradicate with antibiotics. CF patients that develop chronic P. aeruginosa infection have poorer lung function, higher morbidity, and a reduced life expectancy. P. aeruginosa adapts to the CF airway and quickly develops resistance to several antibiotics. A perplexing phenomenon is the disparity between in vitro antimicrobial sensitivity testing and clinical response. Considering the CF airway is host to a diverse community of microorganisms or 'microbiome' and that these microorganisms are known to interact, the antimicrobial resistance and progression of P. aeruginosa infection is likely influenced by these microbial relationships. This review combines the literature to date on interactions between P. aeruginosa and other airway microorganisms and the influence of these interactions on P. aeruginosa tolerance to antimicrobials.

Quorum sensing inhibitory effect of bergamot oil and aspidosperma extract against Chromobacterium violaceum and Pseudomonas aeruginosa

Quorum sensing (QS) represents a major target for reducing bacterial pathogenicity and antibiotic resistance. This study identifies bergamot and aspidosperma as new potential sources of anti-QS agents. We investigated the anti-QS activity of plant materials on both Chromobacterium violaceum and Pseudomonas aeruginosa. Initially, we determined the minimum inhibitory concentrations (MICs) of plant materials using a broth microdilution method. Subsequently, we tested the effect of sub-MIC concentrations on QS-regulated traits and virulence factors production in test bacteria. Results revealed that bergamot and aspidosperma inhibited the ability of C. violaceum to produce violacein. Other QS-controlled phenotypes of C. violaceum, namely chitinolytic activity, motility, and biofilm formation, were also reduced by both plant materials. Moreover, QS-linked traits of P. aeruginosa were also reduced. Bergamot inhibited swarming but not swimming motility, while aspidosperma diminished both motility types in P. aeruginosa. Both plant materials also demonstrated antibiofilm activity and inhibited the production of protease and pyocyanin in P. aeruginosa. Furthermore, we tested the anti-QS effect of plant materials on the transcriptional level using RT-qPCR. Bergamot dramatically downregulated the C. violaceum autoinducer synthase gene cviI and the vioB gene involved in violacein biosynthesis, confirming the phenotypic observation on its anti-QS activity. Aspidosperma also reduced the expression of cviI and vioB but less drastically than bergamot. In P. aeruginosa, downregulation in the transcripts of the QS genes lasI, lasR, rhlI, and rhlR was also achieved by bergamot and aspidosperma. Therefore, data in the present study suggest the usefulness of bergamot and aspidosperma as sources of antivirulence agents.

Growing emergence of drug-resistant Pseudomonas aeruginosa and attenuation of its virulence using quorum sensing inhibitors: A critical review

A perilous increase in the number of bacterial infections has led to developing throngs of antibiotics for increasing the quality and expectancy of life. Pseudomonas aeruginosa is becoming resistant to all known conventional antimicrobial agents thereby posing a deadly threat to the human population. Nowadays, targeting virulence traits of infectious agents is an alternative approach to antimicrobials that is gaining much popularity to fight antimicrobial resistance. Quorum sensing (QS) involves interspecies communication via a chemical signaling pathway. Under this mechanism, cells work in a concerted manner, communicate with each other with the help of signaling molecules called auto-inducers (AI). The virulence of these strains is driven by genes, whose expression is regulated by AI, which in turn acts as transcriptional activators. Moreover, the problem of antibiotic-resistance in case of infections caused by P. aeruginosa becomes more alarming among immune-compromised patients, where the infectious agents easily take over the cellular machinery of the host while hidden in the QS mediated biofilms. Inhibition of the QS circuit of P. aeruginosa by targeting various signaling pathways such as LasR, RhlR, Pqs, and QScR transcriptional proteins will help in blocking downstream signal transducers which could result in reducing the bacterial virulence. The anti-virulence agent does not pose an immediate selective pressure on growing bacterium and thus reduces the pathogenicity without harming the target species. Here, we review exclusively, the growing emergence of multi-drug resistant (MDR) P. aeruginosa and the critical literature survey of QS inhibitors with their potential application of blocking P. aeruginosa infections.

Inverse correlation between biofilm production efficiency and antimicrobial resistance in clinical isolates of Pseudomonas aeruginosa

This study assessed the correlation between biofilm formation in Pseudomonas aeruginosa strains with both the level of antibiotic resistance, and the number of virulence- and biofilm-related genes encoded. A total of sixty-six, non-replicate and prospectively collected P. aeruginosa strains were identified and tested. Potential ampD mutations that may impose resistance to extended-spectrum β-lactam (ESBL) agents were further explored. Of the sixty-six tested isolates, 40 demonstrated the multidrug resistance (MDR) phenotype, while twenty-six were non-MDR strains. An inverse correlation was observed between antibiotic resistance and the potential capacity to form biofilms. In addition, no correlation was observed between novel ampD mutations and the tendency for MDR isolates to acquire a β-lactam-resistant phenotype. The present study emphasizes the need for enhanced infection preventive measures in various hospital units, since both MDR and non-MDR P. aeruginosa isolates exhibited a high level of biofilm-forming capacity and the presence of virulence-associated genes.

Mimicking biofilm formation and development: Recent progress in in vitro and in vivo biofilm models

Biofilm formation in living organisms is associated to tissue and implant infections, and it has also been linked to the contribution of antibiotic resistance. Thus, understanding biofilm development and being able to mimic such processes is vital for the successful development of antibiofilm treatments and therapies. Several decades of research have contributed to building the foundation for developing in vitro and in vivo biofilm models. However, no such thing as an "all fit" in vitro or in vivo biofilm models is currently available. In this review, in addition to presenting an updated overview of biofilm formation, we critically revise recent approaches for the improvement of in vitro and in vivo biofilm models.

What Is in a Cat Scratch? Growth of Bartonella henselae in a Biofilm

Bartonella henselae (B. henselae) is a gram-negative bacterium that causes cat scratch disease, bacteremia, and endocarditis, as well as other clinical presentations. B. henselae has been shown to form a biofilm in vitro that likely plays a role in the establishment and persistence of the bacterium in the host. Biofilms are also known to form in the cat flea vector; hence, the ability of this bacterium to form a biofilm has broad biological significance. The release of B. henselae from a biofilm niche appears to be important in disease persistence and relapse in the vertebrate host but also in transmission by the cat flea vector. It has been shown that the BadA adhesin of B. henselae is critical for adherence and biofilm formation. Thus, the upregulation of badA is important in initiating biofilm formation, and down-regulation is important in the release of the bacterium from the biofilm. We summarize the current knowledge of biofilm formation in Bartonella species and the role of BadA in biofilm formation. We discuss the evidence that defines possible mechanisms for the regulation of the genes required for biofilm formation. We further describe the regulation of those genes in the conditions that mimic both the arthropod vector and the mammalian host for B. henselae. The treatment for persistent B. henselae infection remains a challenge; hence, a better understanding of the mechanisms by which this bacterium persists in its host is critical to inform future efforts to develop drugs to treat such infections.

Novel Chronic Wound Healing by Anti-biofilm Peptides and Protease

Chronic wounds have made a challenge in medical healthcare due to their biofilm infections, which reduce the penetrance of the antibacterial agents in the injury site. In infected wounds, the most common bacterial strains are Staphylococcus aureus and Pseudomonas aeruginosa. Biofilm disruption in chronic wounds is crucial in wound healing. Due to their broad-spectrum antibacterial properties and fewer side effects, anti-biofilm peptides, especially bacteriocins, are promising in the healing of chronic wounds by biofilm destruction. This study reviews the effects of antimicrobial and anti-biofilm agents, including bacteriocins and protease enzymes as a novel approach, on wound healing, along with analyzing the molecular docking between a bacterial protease and biofilm components. Among a large number of anti-biofilm bacteriocins identified up to now, seven types have been registered in the antimicrobial peptides (AMPs) database. Although it is believed that bacterial proteases are harmful in wound healing, it has recently been demonstrated that these proteases like the human serine protease, in combination with AMPs, can improve wound healing by biofilm destruction. In this work, docking results between metalloprotease from Paenibacillus polymyxa and proteins of S. aureus and P. aeruginosa involved in biofilm production, showed that this bacterial protease could efficiently interact with biofilm components. Infected wound healing is an important challenge in clinical trials due to biofilm production by bacterial pathogens. Therefore, simultaneous use of proteases or anti-biofilm peptides with antimicrobial agents could be a promising method for chronic wound healing.

Approaches to Targeting Bacterial Biofilms in Cystic Fibrosis Airways

The treatment of lung infection in the context of cystic fibrosis (CF) is limited by a biofilm mode of growth of pathogenic organisms. When compared to planktonically grown bacteria, bacterial biofilms can survive extremely high levels of antimicrobials. Within the lung, bacterial biofilms are aggregates of microorganisms suspended in a matrix of self-secreted proteins within the sputum. These structures offer both physical protection from antibiotics as well as a heterogeneous population of metabolically and phenotypically distinct bacteria. The bacteria themselves and the components of the extracellular matrix, in addition to the signaling pathways that direct their behaviour, are all potential targets for therapeutic intervention discussed in this review. This review touches on the successes and failures of current anti-biofilm strategies, before looking at emerging therapies and the mechanisms by which it is hoped they will overcome current limitations.

Microbes of the human eye: Microbiome, antimicrobial resistance and biofilm formation

BACKGROUND

The review focuses on the bacteria associated with the human eye using the dual approach of detecting cultivable bacteria and the total microbiome using next generation sequencing. The purpose of this review was to highlight the connection between antimicrobial resistance and biofilm formation in ocular bacteria.

METHODS

Pubmed was used as the source to catalogue culturable bacteria and ocular microbiomes associated with the normal eyes and those with ocular diseases, to ascertain the emergence of anti-microbial resistance with special reference to biofilm formation.

RESULTS

This review highlights the genetic strategies used by microorganisms to evade the lethal effects of anti-microbial agents by tracing the connections between candidate genes and biofilm formation.

CONCLUSION

The eye has its own microbiome which needs to be extensively studied under different physiological conditions; data on eye microbiomes of people from different ethnicities, geographical regions etc. are also needed to understand how these microbiomes affect ocular health.

A Potential Quorum-Sensing Inhibitor for Bronchiectasis Therapy: Quercetin-Chitosan Nanoparticle Complex Exhibiting Superior Inhibition of Biofilm Formation and Swimming Motility of Pseudomonas aeruginosa to the Native Quercetin

Quercetin (QUE)—a plant-derived flavonoid, is recently established as an effective quorum sensing (QS) inhibiting agent in Pseudomonas aeruginosa—the main bacterial pathogen in bronchiectasis lungs. Successful clinical application of QUE, however, is hindered by its low solubility in physiological fluids. Herein we developed a solubility enhancement strategy of QUE in the form of a stable amorphous nanoparticle complex (nanoplex) of QUE and chitosan (CHI), which was prepared by electrostatically driven complexation between ionized QUE molecules and oppositely charged CHI. At its optimal preparation condition, the QUE–CHI nanoplex exhibited a size of roughly 150 nm with a 25% QUE payload and 60% complexation efficiency. The complexation with CHI had no adverse effect on the antibacterial and anticancer activities of QUE, signifying the preservation of QUE’s bioactivities in the nanoplex. Compared to the native QUE, the QUE–CHI nanoplex exhibited superior QS inhibition in suppressing the QS-regulated swimming motility and biofilm formation of P. aeruginosa, but not in suppressing the virulence factor production. The superior inhibitions of the biofilm formation and swimming motility afforded by the nanoplex were attributed to (1) its higher kinetic solubility (5-times higher) that led to higher QUE exposures, and (2) the synergistic QS inhibition attributed to its CHI fraction.

Pseudomonas chlororaphis PA23 metabolites protect against protozoan grazing by the predator Acanthamoeba castellanii

Background

Pseudomonas chlororaphis strain PA23 is a biocontrol agent that is able to protect canola against the pathogenic fungus Sclerotinia sclerotiorum. This bacterium secretes a number of metabolites that contribute to fungal antagonism, including pyrrolnitrin (PRN), phenazine (PHZ), hydrogen cyanide (HCN) and degradative enzymes. In order to be successful, a biocontrol agent must be able to persist in the environment and avoid the threat of grazing predators. The focus of the current study was to investigate whether PA23 is able to resist grazing by the protozoan predator Acanthamoeba castellanii (Ac) and to define the role of bacterial metabolites in the PA23-Ac interaction.

Methods

Ac was co-cultured with PA23 WT and a panel of derivative strains for a period of 15 days, and bacteria and amoebae were enumerated on days 1, 5, 10 and 15. Ac was subsequently incubated in the presence of purified PRN, PHZ, and KCN and viability was assessed at 24, 48 and 72 h. Chemotactic assays were conducted to assess whether PA23 compounds exhibit repellent or attractant properties towards Ac. Finally, PA23 grown in the presence and absence of amoebae was subject to phenotypic characterization and gene expression analyses.

Results

PRN, PHZ and HCN were found to contribute to PA23 toxicity towards Ac trophozoites, either by killing or inducing cyst formation. This is the first report of PHZ-mediated toxicity towards amoebae. In chemotaxis assays, amoebae preferentially migrated towards regulatory mutants devoid of extracellular metabolite production as well as a PRN mutant, indicating this antibiotic has repellent properties. Co-culturing of bacteria with amoebae led to elevated expression of the PA23 phzI/phzR quorum-sensing (QS) genes and phzA and prnA, which are under QS control. PHZ and PRN levels were similarly increased in Ac co-cultures, suggesting that PA23 can respond to predator cues and upregulate expression of toxins accordingly.

Conclusions

PA23 compounds including PRN, PHZ and HCN exhibited both toxic and repellent effects on Ac. Co-culturing of bacteria and amoebae lead to changes in bacterial gene expression and secondary metabolite production, suggesting that PA23 can sense the presence of these would-be predators and adjust its physiology in response.