Bacterial biofilm and associated infections

Surface modification strategies for hemodialysis catheters to prevent catheter-related infections: A review

Insertion of a central venous catheter is one of the most common invasive procedures applied in hemodialysis therapy for end-stage renal disease. The most important complication of a central venous catheter is catheter-related infections that increase hospitalization and duration of intensive care unit stay, cost of treatment, mortality, and morbidity rates. Pathogenic microorganisms, such as, bacteria and fungi, enter the body from the catheter insertion site and the surface of the catheter can become colonized. The exopolysaccharide-based biofilms from bacterial colonies on the surface are the main challenge in the treatment of infections. Catheter lock solutions and systemic antibiotic treatment, which are commonly used in the treatment of hemodialysis catheter-related infections, are insufficient to prevent and terminate the infections and eventually the catheter needs to be replaced. The inadequacy of these approaches in termination and prevention of infection revealed the necessity of coating of hemodialysis catheters with bactericidal and/or antiadhesive agents. Silver compounds and nanoparticles, anticoagulants (e.g., heparin), antibiotics (e.g., gentamicin and chlorhexidine) are some of the agents used for this purpose. The effectiveness of few commercial hemodialysis catheters that were coated with antibacterial agents has been tested in clinical trials against catheter-related infections of pathogenic bacteria, such as Staphylococcus aureus and Staphylococcus epidermidis with promising results. Novel biomedical materials and engineering techniques, such as, surface micro/nano patterning and the conjugation of antimicrobial peptides, enzymes, metallic cations, and hydrophilic polymers (e.g., poly [ethylene glycol]) on the surface, has been suggested recently.

Bacteriophage-derived endolysins to target gram-negative bacteria

Bacteriophage-encoded endolysins (lysins) have emerged as a novel class of antibacterial agents to combat the surging antibiotic resistance. Lysins have specific structures and mechanisms to exert antibacterial effect against both Gram-positive (G+ve) and Gram-negative (G-ve) bacteria. However, its use against G-ve bacteria is limited because the outer membrane (OM) of G-ve bacteria hinders the permeation of exogenously applied lysins. Besides identifying lysins with intrinsic OM permeability, several other approaches including combining lysins with outer membrane permeabilizers (OMPs), protein engineering and formulating with nanocarriers have been proposed to enhance the permeability and activity of lysins. In the present review, we summarize strategies that have been developed to enable lysins to target G-ve bacteria in the past decade. While lysins demonstrates clear potential in managing bacterial infections caused by the drug-resistant G-ve bacteria, there are still challenges hindering their translation into clinical settings, including safety issues with OMP use, low efficiency against stationary phase bacteria and problems in stability. The applicability of protein engineering and formulation sciences to improve enzyme stability, and combination therapy with other classes of antibacterial agents to maximize the therapeutic potential have also been reviewed.

The Role of Bacterial Biofilm in Antibiotic Resistance and Food Contamination

Biofilm is a microbial association or community attached to different biotic or abiotic surfaces or environments. These surface-attached microbial communities can be found in food, medical, industrial, and natural environments. Biofilm is a critical problem in the medical sector since it is formed on medical implants within human tissue and involved in a multitude of serious chronic infections. Food and food processing surface become an ideal environment for biofilm formation where there are sufficient nutrients for microbial growth and attachment. Therefore, biofilm formation on these surfaces, especially on food processing surface becomes a challenge in food safety and human health. Microorganisms within a biofilm are encased within a matrix of extracellular polymeric substances that can act as a barrier and recalcitrant for different hostile conditions such as sanitizers, antibiotics, and other hygienic conditions. Generally, they persist and exist in food processing environments where they become a source of cross-contamination and foodborne diseases. The other critical issue with biofilm formation is their antibiotic resistance which makes medication difficult, and they use different physical, physiological, and gene-related factors to develop their resistance mechanisms. In order to mitigate their production and develop controlling methods, it is better to understand growth requirements and mechanisms. Therefore, the aim of this review article is to provide an overview of the role of bacterial biofilms in antibiotic resistance and food contamination and emphasizes ways for controlling its production.

Activity of Antimicrobial Peptides and Ciprofloxacin against Pseudomonas aeruginosa Biofilms

Pseudomonas aeruginosa is increasingly resistant to conventional antibiotics, which can be compounded by the formation of biofilms on surfaces conferring additional resistance. P. aeruginosa was grown in sub-inhibitory concentrations of the antimicrobial peptides (AMPs) melimine and Mel4 or ciprofloxacin for 30 consecutive days to induce the development of resistance. Antibiofilm effect of AMPs and ciprofloxacin was evaluated using crystal violet and live/dead staining with confocal microscopy. Effect on the cell membrane of biofilm cells was evaluated using DiSC(3)-5 dye and release of intracellular ATP and DNA/RNA. The minimum inhibitory concentration (MIC) of ciprofloxacin increased 64-fold after 30 passages, but did not increase for melimine or Mel4. Ciprofloxacin could not inhibit biofilm formation of resistant cells at 4× MIC, but both AMPs reduced biofilms by >75% at 1× MIC. At 1× MIC, only the combination of either AMP with ciprofloxacin was able to significantly disrupt pre-formed biofilms (≥61%; p < 0.001). Only AMPs depolarized the cell membranes of biofilm cells at 1× MIC. At 1× MIC either AMP with ciprofloxacin released a significant amount of ATP (p < 0.04), but did not release DNA/RNA. AMPs do not easily induce resistance in P. aeruginosa and can be used in combination with ciprofloxacin to treat biofilm.

A rapid model for developing dry surface biofilms of Staphylococcus aureus and Pseudomonas aeruginosa for in vitro disinfectant efficacy testing

Background

Bacterial biofilms persistent on dry environmental surfaces in healthcare facilities play an important role in the occurrence of healthcare associated infections (HAI). Compared to wet surface biofilms and planktonic bacteria, dry surface biofilms (DSB) are more tolerant to disinfection. However, there is no official method for developing DSB for in vitro disinfectant efficacy testing. The objectives of this study were to (i) develop an in vitro model of DSB of S. aureus and P. aeruginosa for disinfectant efficacy testing and (ii) investigate the effect of drying times and temperatures on DSB development. We hypothesized that a minimum six log₁₀ density of DSB could be achieved on glass coupons by desiccating wet surface biofilms near room temperatures. We also hypothesized that a DSB produced by the model in this study will be encased in extracellular polymeric substances (EPS).

Methods

S. aureus ATCC-6538 and P. aeruginosa ATCC-15442 wet surface biofilms were grown on glass coupons following EPA MLB SOP MB-19. A DSB model was developed by drying coupons in an incubator and viable bacteria were recovered following a modified version of EPA MLB SOP MB-20. Scanning electron microscopy was used to confirm the EPS presence on DSB.

Results

Overall, a minimum of six mean log₁₀ densities of DSB for disinfectant efficacy were recovered per coupon after drying at different temperatures and drying times. Regardless of strain, temperature and dry time, 86% of coupons with DSB were confirmed to have EPS.

Conclusion

A rapid model for developing DSB with characteristic EPS was developed for disinfectant efficacy testing against DSB.

Alcohol dehydrogenase modulates quorum sensing in biofilm formations of Acinetobacter baumannii

Acinetobacter baumannii (A. baumannii) is a common opportunistic nosocomial pathogen, which is able to produce biofilms on the surface of indwelling medical devices, and consequentially causes severe infections in clinical settings. In order to identify genes that involved in the biofilm formation of A. baumannii, the differential expression of genes between biofilms and planktonic cells was analyzed by RNAseq assay and validated in clinical isolates. The RNAseq data showed that 264 genes were up-regulated, while 240 genes were down-regulated in the biofilms of A. baumannii. Among them, the gene encoding alcohol dehydrogenase (ADH), a known molecule of bacterial quorum sensing (QS) system that plays a key role in biofilm formation bacteria, was one of the most up-regulated gene in both reference strains and clinical isolates. Functional studies using ADH inhibitor disulfiram and activator taurine further demonstrated that the presence of disulfiram significantly inhibit the cell growth, motility and biofilm formation, paralleled by a decreased expression of QS-related genes, including AbaI, A1S_0109, and A1S_0112, in a dose-dependent manner; vice versa, the addition of ADH activator taurine, and QS molecule C12- homoserine lactone synthase (HSL) led a dose-dependent increase of bacterial growth, motility and biofilm production, along with an increased expression of QS-related genes in both reference strains and clinical isolates of A. baumannii. These results suggested that the ADH was a key molecule able to modulate the QS system and promote the biofilm formation, growth and motility in A. baumannii.

Microbial biofilm ecology, in silico study of quorum sensing receptor-ligand interactions and biofilm mediated bioremediation

Biofilms are structured microbial communities of single or multiple populations in which microbial cells adhere to a surface and get embedded in extracellular polymeric substances (EPS). This review attempts to explain biofilm architecture, development phases, and forces that drive bacteria to promote biofilm mode of growth. Bacterial chemical communication, also known as Quorum sensing (QS), which involves the production, detection, and response to small molecules called autoinducers, is highlighted. The review also provides a brief outline of interspecies and intraspecies cell-cell communication. Additionally, we have performed docking studies using Discovery Studio 4.0, which has enabled our understanding of the prominent interactions between autoinducers and their receptors in different bacterial species while also scoring their interaction energies. Receptors, such as LuxN (Phosphoreceiver domain and RecA domain), LuxP, and LuxR, interacted with their ligands (AI-1, AI-2, and AHL) with a CDocker interaction energy of - 31.6083 kcal/mole; - 34.5821 kcal/mole, - 48.2226 kcal/mole and - 41.5885 kcal/mole, respectively. Since biofilms are ideal for the remediation of contaminants due to their high microbial biomass and their potential to immobilize pollutants, this article also provides an overview of biofilm-mediated bioremediation.

Antimicrobial Peptide Cec4 Eradicates the Bacteria of Clinical Carbapenem-Resistant Acinetobacter baumannii Biofilm

The drug resistance rate of Acinetobacter baumannii increases year on year, and the drugs available for the treatment of carbapenem-resistant A. baumannii (CRAB) infection are extremely limited. A. baumannii, which forms biofilms, protects itself by secreting substrates such as exopolysaccharides, allowing it to survive under adverse conditions and increasing drug resistance. Antimicrobial peptides are small molecular peptides with broad-spectrum antibacterial activity and immunomodulatory function. Previous studies have shown that the antimicrobial peptide Cec4 has a strong effect on A. baumannii, but the antibacterial and biofilm inhibition of this antimicrobial peptide on clinical carbapenem resistance A. baumannii is not thoroughly understood. In this study, it was indicated that most of the 200 strains of CRAB were susceptible to Cec4 with a MIC of 4 μg/ml. Cec4 has a strong inhibitory and eradication effect on the CRAB biofilm; the minimum biofilm inhibition concentration (MBIC) was 64–128 μg/ml, and the minimum biofilm eradication concentration (MBEC) was 256–512 μg/ml. It was observed that Cec4 disrupted the structure of the biofilm using scanning electron microscopy (SEM) and confocal laser scanning microscopy (CLSM). A comparative transcriptome analysis of the effects of the antimicrobial peptide Cec4 on CRAB biofilm, identified 185 differentially expressed genes, including membrane proteins, bacterial resistance genes, and pilus-related genes. The results show that multiple metabolic pathways, two-component regulation systems, quorum sensing, and antibiotic synthesis-related pathways in A. baumannii biofilms were affected after Cec4 treatment. In conclusion, Cec4 may represent a new choice for the prevention and treatment of clinical infections, and may also provide a theoretical basis for the development of antimicrobial peptide drugs.

Computational investigation for modeling the protein-protein interaction of TasA(28-261)-TapA(33-253): a decisive process in biofilm formation by Bacillus subtilis

Biofilms have a significant role in microbial persistence, antibiotic resistance, and chronic infections; consequently, there is a pressing need for development of novel "anti-biofilm strategies." One of the fundamental mechanisms involved in biofilm formation is protein-protein interactions of "amyloid-like proteins" (ALPs) in the extracellular matrix. Such interactions could be potential targets for development of novel anti-biofilm strategies; therefore, assessing the structural features of these interactions could be of great scientific value. Characterization of structural features the of protein-protein interaction with conventional structure biology tools including X-ray diffraction and nuclear magnetic resonance is technically challenging, expensive, and time-consuming. In contrast, modeling such interactions is time-efficient and economical, and might provide deeper understanding of structural basis of interactions. Although it is often acknowledged that molecular modeling methods have varying accuracy, their careful implementation with supplementary verification methods can provide valuable insight and directions for future studies. With this reasoning, during the present study, the protein-protein interaction of TasA_(28-261)-TapA_(33-253) (which is a decisive process for biofilm formation by Bacillus subtilis) was modeled using in silico approaches, viz., molecular modeling, protein-protein docking, and molecular dynamics simulations. Results obtained here identified amino acid residues present within intrinsically disordered regions of both proteins to be critical for interaction. These results were further supported with principal component analyses (PCA) and free energy landscape (FEL) analyses. Results presented here represent novel finding, and we hypothesize that amino acid residues identified during the present study could be targeted for inhibition of biofilm formation by B. subtilis.

High Efficacy of Ozonated Oils on the Removal of Biofilms Produced by Methicillin-Resistant Staphylococcus aureus (MRSA) from Infected Diabetic Foot Ulcers

Ozone has a high wound healing capacity and antibacterial properties and can be used as a complementary treatment in infections. Methicillin-resistant S. aureus (MRSA) is the most common pathogen found in infected diabetic foot ulcers. Most of MRSA are resistant to several classes of antibiotics and, therefore, there is a need for new, effective, and well-tolerated agents. Thus, we aimed evaluate the antimicrobial and antibiofilm potentials of ozonated vegetable oils against MRSA strains isolated from diabetic foot ulcers. Six ozonated oils were produced with concentrations of ozone ranging from 0.53 to 17 mg of ozone/g of oil. The peroxide values were determined for each oil. Ozonated oils content on fatty acid was determined by gas chromatography equipped with a flame ionization detector. The antimicrobial susceptibility testing was performed by the Kirby–Bauer disk diffusion method and the effect of ozonated oils on biofilm formation ability and on established biofilms was investigated. In general, the content in identified unsaturated fatty acid in oils decreased with the increase of ozonation time and, consequently, the peroxide value increased. Most bacterial strains were inhibited by ozonated oil at a concentration of 4.24 mg/g. Ozonated oils had moderate to high ability to remove adhered cells and showed a high capacity to eradicate 24 h old biofilms. Our results show promising use of ozonated oils on the treatment of infections, in particular those caused by multidrug-resistant MRSA strains.

Microbial biofilms in nature: unlocking their potential for agricultural applications

Soil environments are dynamic and the plant rhizosphere harbours a phenomenal diversity of micro-organisms which exchange signals and beneficial nutrients. Bipartite beneficial or symbiotic interactions with host roots, such as mycorrhizae and various bacteria, are relatively well characterized. In addition, a tripartite interaction also exists between plant roots, arbuscular mycorrhizal fungi (AMF) and associated bacteria. Bacterial biofilms exist as a sheet of bacterial cells in association with AMF structures, embedded within a self-produced exopolysaccharide matrix. Such biofilms may play important functional roles within these tripartite interactions. However, the details about such interactions in the rhizosphere and their relevant functional relationships have not been elucidated. This review explores the current understanding of naturally occurring microbial biofilms, and their interaction with biotic surfaces, especially AMF. The possible roles played by bacterial biofilms and the potential for their application for a more productive and sustainable agriculture is discussed in this review.

Tannic acid-modified silver nanoparticles for enhancing anti-biofilm activities and modulating biofilm formation

The formation of bacterial biofilms is a key factor in the emergence of chronic infections due to the strong resistance of biofilms to conventional antibiotics. There is an urgent need to develop an effective strategy to control the formation of biofilms. In this study, a nanocomposite of tannic acid and silver (Tannin-AgNPs) was designed and successfully prepared based on the quorum sensing (QS) inhibitory activity of tannic acid and the anti-bacterial activity of silver. The dynamic light scattering and SEM observations indicated that the obtained Tannin-AgNPs were spherical with a mean particle size of 42.37 nm. Tannic acid was successfully modified on the surface of silver nanoparticles and characterized via Fourier transform infrared (FTIR) spectroscopy. The prepared Tannin-AgNPs demonstrated a more effective anti-bacterial and anti-biofilm activity against E. coli than the unmodified AgNPs or tannic acid. In addition, the Tannin-AgNPs can modulate the formation process of E. coli biofilms, shorten the growth period of biofilms and extend the dispersion period of biofilms. Tannin-AgNPs also showed the function of decreasing the production of the QS signal molecule. The proposed strategy of constructing a nanocomposite using AgNPs and natural components with QS inhibitory activity is effective and promising for inhibiting the formation of biofilms.

Promising Therapeutic Strategies Against Microbial Biofilm Challenges

Biofilms are communities of microorganisms that are attached to a biological or abiotic surface and are surrounded by a self-produced extracellular matrix. Cells within a biofilm have intrinsic characteristics that are different from those of planktonic cells. Biofilm resistance to antimicrobial agents has drawn increasing attention. It is well-known that medical device- and tissue-associated biofilms may be the leading cause for the failure of antibiotic treatments and can cause many chronic infections. The eradication of biofilms is very challenging. Many researchers are working to address biofilm-related infections, and some novel strategies have been developed and identified as being effective and promising. Nevertheless, more preclinical studies and well-designed multicenter clinical trials are critically needed to evaluate the prospects of these strategies. Here, we review information about the mechanisms underlying the drug resistance of biofilms and discuss recent progress in alternative therapies and promising strategies against microbial biofilms. We also summarize the strengths and weaknesses of these strategies in detail.

Potential Synergistic Action of Bioactive Compounds from Plant Extracts against Skin Infecting Microorganisms

The skin is an important organ that acts as a physical barrier to the outer environment. It is rich in immune cells such as keratinocytes, Langerhans cells, mast cells, and T cells, which provide the first line of defense mechanisms against numerous pathogens by activating both the innate and adaptive response. Cutaneous immunological processes may be stimulated or suppressed by numerous plant extracts via their immunomodulatory properties. Several plants are rich in bioactive molecules; many of these exert antimicrobial, antiviral, and antifungal effects. The present study describes the impact of plant extracts on the modulation of skin immunity, and their antimicrobial effects against selected skin invaders. Plant products remain valuable counterparts to modern pharmaceuticals and may be used to alleviate numerous skin disorders, including infected wounds, herpes, and tineas.

Tolerability and safety of urotainer® polihexanide 0.02% in catheterized patients: a prospective cohort study

Background

In patients with indwelling bladder catheters for > 2 weeks, bacterial colonization is inevitable, leading to urinary tract infections or encrustations with subsequent catheter blockage. Currently, bladder irrigations are the most frequently used prophylactic means, but the best solution remains yet to be determined. In vitro studies demonstrate that polihexanide is a promising option for catheter irrigation, but no data about safety and tolerability exist.

Methods

In a prospective observational study in patients with indwelling bladder catheter for > 2 weeks, a 0.02% polihexanide solution was used to rinse the catheter on five consecutive days. Adverse events, tolerability and vital signs were assessed before, during, after and at the end of the treatment period.

Results

There was no serious adverse event in the study. A total of 28 adverse events (AEs) in 15 (46.88%) participants were experienced. Absolute changes in pain scores were not clinically relevant. No incidences of either flushing or sweating were found during instillation. Bladder spasms during instillation were reported in two cases during a single instillation. Mean pulse rates did not change by more than 3 beats per minute. Mean changes in body temperature did not exceed 0.12 °C. Clinically relevant changes in blood pressure were recorded for 3 patients.

Conclusions

This is the first study to demonstrate that a 0.02% polihexanide solution can safely be used for catheter irrigation.

Trial registration

ClinicalTrials.gov (NCT02157415), June 6th, 2014.

Cystic Fibrosis: Overview of the Current Development Trends and Innovative Therapeutic Strategies

Cystic Fibrosis (CF), an autosomal recessive genetic disease, is caused by a mutation in the gene encoding the cystic fibrosis transmembrane conductance regulator (CFTR). This mutation reduces the release of chloride ions (Cl-) in epithelial tissues, and hyperactivates the epithelial sodium channels (ENaC) which aid in the absorption of sodium ions (Na+). Consequently, the mucus becomes dehydrated and thickened, making it a suitable medium for microbial growth. CF causes several chronic lung complications like thickened mucus, bacterial infection and inflammation, progressive loss of lung function, and ultimately, death. Until recently, the standard of clinical care in CF treatment had focused on preventing and treating the disease complications. In this review, we have summarized the current knowledge on CF pathogenesis and provided an outlook on the current therapeutic approaches relevant to CF (i.e., CFTR modulators and ENaC inhibitors). The enormous potential in targeting bacterial biofilms using antibiofilm peptides, and the innovative therapeutic strategies in using the CRISPR/Cas approach as a gene-editing tool to repair the CFTR mutation have been reviewed. Finally, we have discussed the wide range of drug delivery systems available, particularly non-viral vectors, and the optimal properties of nanocarriers which are essential for successful drug delivery to the lungs.

Photothermal Antibacterial and Antibiofilm Activity of Black Phosphorus/Gold Nanocomposites against Pathogenic Bacteria

Black phosphorus (BP) as a layered two-dimensional (2D) semiconductor material with a tunable band gap has attracted growing attention for promising applications in diverse fields including biotechnology owing to its excellent physical and chemical properties. In this study, BP crystals were synthesized using a chemical vapor transport method and exfoliated into BP nanosheets in deoxygenated water or hexane. Next, monodisperse Au nanoparticles that were synthesized using a surfactant-assisted chemical reduction method were assembled on exfoliated BP nanosheets hexane to yield BP/Au nanocomposites. The photothermal antibacterial and antibiofilm activities of BP nanosheets and BP/Au nanocomposites were investigated against Enterococcus faecalis, a pathogenic biofilm-forming bacterium, by studying the photothermal effect and bacterial growth curve and using colony counting and live/dead fluorescence staining methods under near-infrared (NIR) light irradiation. Thanks to the higher photothermal conversion efficiency of BP/Au nanocomposites than that of bare BP nanosheets under NIR light irradiation, they destructed the bacterial cell membrane more efficiently than bare BP with the biofilm inhibition rate of 58%. It should be noted that this is the first study on the antibacterial and antibiofilm activity of BP/Au nanocomposites via a photothermal process under NIR light irradiation. This work shows the potential of BP/Au nanocomposites in fighting against pathogenic bacteria and paves the way for the exploration of antibacterial platforms based on the biocompatible 2D semiconductor BP.

Profiling and Role of Bioactive Molecules from Puntius sophore (Freshwater/Brackish Fish) Skin Mucus with Its Potent Antibacterial, Antiadhesion, and Antibiofilm Activities

Epidermal fish mucus comprises of diverse bioactive metabolites which plays an immense role in defense mechanisms and other important cellular activities. Primarily, this study aims to screen the unexplored mucus extract of Puntius sophore(P. sophore) for its antagonistic potential against common pathogens, which are commonly implicated in foodborne and healthcare associated infections, with effects on their adhesion and biofilm formation. Profiling of the skin mucus was carried out by High Resolution-Liquid Chromatography Mass Spectrometry (HR-LCMS), followed by antibacterial activity and assessment of antibiofilm potency and efficacy on the development, formation, and texture of biofilms. Furthermore, bacterial cell damage, viability within the biofilm, checkerboard test, and cytotoxicity were also evaluated. As a result, P. sophore mucus extract was found to be effective against all tested strains. It also impedes the architecture of biofilm matrix by affecting the viability and integrity of bacterial cells within biofilms and reducing the total exopolysaccharide content. A synergy was observed between P. sophore mucus extract and gentamicin for Escherichia coli(E. coli), Pseudomonas aeruginosa(P. aeruginosa), and Bacillus subtilis(B. subtilis), whereas, an additive effect for Staphylococcus aureus(S. aureus). Thus, our findings represent the potent bioactivities of P. sophore mucus extract for the first time, which could be explored further as an alternative to antibiotics or chemically synthesized antibiofilm agents.

Association between Biofilm-Production and Antibiotic Resistance in Uropathogenic Escherichia coli (UPEC): An In Vitro Study

Urinary tract infections (UTIs) are among the most common infections requiring medical attention worldwide. The production of biofilms is an important step in UTIs, not only from a mechanistic point of view, but this may also confer additional resistance, distinct from other aspects of multidrug resistance (MDR). A total of two hundred and fifty (n = 250) Escherichia coli isolates, originating from clean-catch urine samples, were included in this study. The isolates were classified into five groups: wild-type, ciprofloxacin-resistant, fosfomycin-resistant, trimethoprim-sulfamethoxazole-resistant and extended spectrum β-lactamase (ESBL)-producing strains. The bacterial specimens were cultured using eosine methylene blue agar and the colony morphology of isolates were recorded. Antimicrobial susceptibility testing was performed using the Kirby-Bauer disk diffusion method and E-tests. Biofilm-formation of the isolates was carried out with the crystal violet tube-adherence method. n = 76 isolates (30.4%) produced large colonies (>3 mm), mucoid variant colonies were produced in n = 135 cases (54.0%), and n = 119 (47.6%) were positive for biofilm formation. The agreement (i.e., predictive value) of mucoid variant colonies in regard to biofilm production in the tube-adherence assay was 0.881 overall. Significant variation was seen in the case of the group of ESBL-producers in the ratio of biofilm-producing isolates. The relationship between biofilm-production and other resistance determinants has been extensively studied. However, no definite conclusion can be reached from the currently available data.

Antimicrobial and antibiofilm activities of ursolic acid against carbapenem-resistant Klebsiella pneumoniae

Previous studies demonstrated that ursolic acid (UA) present in apple pomace displays antimicrobial activity against some microorganisms, but the underlying mechanisms associated with this activity remain unexplored. Furthermore, there are no reports on the effect of UA on carbapenem-resistant Klebsiella pneumoniae (CRKP). This study examined the antimicrobial activity and mode of action of UA against CRKP was examined. Minimum inhibitory concentration (MIC) of UA against CRKP was determined by the agar dilution method. Variations in the intracellular pH (pHin), ATP concentration, and cell membrane potential were measured to assess the influence of UA on the cell membrane. Our results show that UA was effective against CRKP at an MIC of 0.8 mg ml-1. UA disrupted the cell membrane integrity of CRKP, exhibited strong inhibitory effects against biofilm formation and biofilm-related gene expression, and inactivated CRKP cells encased in biofilms. Thus, UA shows promise for use in combination with other antibiotics to treat multidrug resistant K. pneumoniae infections.

Bioactive Properties of Syzygium cumini (L.) Skeels Pulp and Seed Phenolic Extracts

The emergence of bacterial strains resistant to different antibiotics has prompted the search for new sources of antimicrobial compounds. Studies have shown that jambolan [Syzygium cumini (L.) Skeels], a tropical fruit from the Mirtaceae family, contains a great variety of phytochemical compounds with high antioxidant and antimicrobial activity. This study aimed to determine the centesimal composition and physicochemical characteristics of the pulp and seed of S. cumini (L.) Skeels, as well as the content of total phenolic compounds and the antioxidant, antibacterial, antibiofilm and anti-quorum sensing (QS) activities of the phenolic extracts obtained from the pulp and the seeds of this fruit. The in vitro antibacterial and anti-QS activities of active films incorporating phenolic extracts were also evaluated. Additionally, we performed molecular docking of phenolic compounds present in jambolan with the CviR QS regulator of Chromobacterium violaceum. The composition and physicochemical characteristics of the samples presented similar values to those found for the species. However, the seed phenolic extract had a higher content of phenolic compounds and antioxidant activity than the pulp. Both phenolic extracts presented antibacterial activity against Aeromonas hydrophila, C. violaceum, Escherichia coli, Pseudomonas aeruginosa, Salmonella enterica serovar Typhimurium, Serratia marcescens, Listeria monocytogenes, and Staphylococcus aureus. The seed phenolic extract was particularly inhibitory against S. aureus. The pulp phenolic extract inhibited swarming motility and biofilm formation of A. hydrophila, E. coli, and S. marcescens in sub-MIC concentrations. The pulp and seed phenolic extracts inhibited violacein production in C. violaceum. Films incorporating both phenolic extracts inhibited the growth of bacteria, particularly Pseudomonas fluorescens, L. monocytogenes, and S. aureus, as well as QS in C. violaceum. Molecular docking showed that a variety of compounds found in pulp and seed extracts of jambolan, particularly chlorogenic acid and dihydroquercetin, potentially bind CviR protein and may interfere with QS. Our results indicate that pulp and seed of jambolan are good sources of antibacterial, antibiofilm, and anti-QS compounds that can be used in the development of natural preservatives and for application in antibacterial active films.

Beyond Risk: Bacterial Biofilms and Their Regulating Approaches

Bacterial biofilms are complex surface attached communities of bacteria held together by self-produced polymer matrixs mainly composed of polysaccharides, secreted proteins, and extracellular DNAs. Bacterial biofilm formation is a complex process and can be described in five main phases: (i) reversible attachment phase, where bacteria non-specifically attach to surfaces; (ii) irreversible attachment phase, which involves interaction between bacterial cells and a surface using bacterial adhesins such as fimbriae and lipopolysaccharide (LPS); (iii) production of extracellular polymeric substances (EPS) by the resident bacterial cells; (iv) biofilm maturation phase, in which bacterial cells synthesize and release signaling molecules to sense the presence of each other, conducing to the formation of microcolony and maturation of biofilms; and (v) dispersal/detachment phase, where the bacterial cells depart biofilms and comeback to independent planktonic lifestyle. Biofilm formation is detrimental in healthcare, drinking water distribution systems, food, and marine industries, etc. As a result, current studies have been focused toward control and prevention of biofilms. In an effort to get rid of harmful biofilms, various techniques and approaches have been employed that interfere with bacterial attachment, bacterial communication systems (quorum sensing, QS), and biofilm matrixs. Biofilms, however, also offer beneficial roles in a variety of fields including applications in plant protection, bioremediation, wastewater treatment, and corrosion inhibition amongst others. Development of beneficial biofilms can be promoted through manipulation of adhesion surfaces, QS and environmental conditions. This review describes the events involved in bacterial biofilm formation, lists the negative and positive aspects associated with bacterial biofilms, elaborates the main strategies currently used to regulate establishment of harmful bacterial biofilms as well as certain strategies employed to encourage formation of beneficial bacterial biofilms, and highlights the future perspectives of bacterial biofilms.

Phages for Biofilm Removal

Biofilms are clusters of bacteria that live in association with surfaces. Their main characteristic is that the bacteria inside the biofilms are attached to other bacterial cells and to the surface by an extracellular polymeric matrix. Biofilms are capable of adhering to a wide variety of surfaces, both biotic and abiotic, including human tissues, medical devices, and other materials. On these surfaces, biofilms represent a major threat causing infectious diseases and economic losses. In addition, current antibiotics and common disinfectants have shown limited ability to remove biofilms adequately, and phage-based treatments are proposed as promising alternatives for biofilm eradication. This review analyzes the main advantages and challenges that phages can offer for the elimination of biofilms, as well as the most important factors to be taken into account in order to design effective phage-based treatments.

An Inactive Dispersin B Probe for Monitoring PNAG Production in Biofilm Formation

The bacterial exopolysaccharide poly-β-1,6-N-acetylglucosamine is a major extracellular matrix component in biofilms of both Gram-positive and Gram-negative organisms. We have leveraged the specificity of the biofilm-dispersing glycoside hydrolase Dispersin B (DspB) to generate a probe (Dispersin B PNAG probe, DiPP) for monitoring PNAG production and localization during biofilm formation. Mutation of the active site of Dispersin B gave DiPP, which was an effective probe despite its low affinity for PNAG oligosaccharides (K_D ∼ 1-10 mM). Imaging of PNAG-dependent and -independent biofilms stained with a fluorescent-protein fusion of DiPP (GFP-DiPP) demonstrated the specificity of the probe for the structure of PNAG on both single-cell and biofilm levels, indicating a high local concentration of PNAG at the bacterial cell surface. Through quantitative bacterial cell binding assays and confocal microscopy analysis using GFP-DiPP, discrete areas of local high concentrations of PNAG were detected on the surface of early log phase cells. These distinct areas were seen to grow, slough from cells, and accumulate in interbacterial regions over the course of several cell divisions, showing the development of a PNAG-dependent biofilm. A potential helical distribution of staining was also noted, suggesting some degree of organization of PNAG production at the cell surface prior to cell aggregation. Together, these experiments shed light on the early stages of PNAG-dependent biofilm formation and demonstrate the value of a low-affinity-high-specificity probe for monitoring the production of bacterial exopolysaccharides.

Encapsulation of Essential Oils via Nanoprecipitation Process: Overview, Progress, Challenges and Prospects

Essential oils are of paramount importance in pharmaceutical, cosmetic, agricultural, and food areas thanks to their crucial properties. However, stability and bioactivity determine the effectiveness of essential oils. Polymeric nanoencapsulation is a well-established approach for the preservation of essential oils. It offers a plethora of benefits, including improved water solubility, effective protection against degradation, prevention of volatile components evaporation and controlled and targeted release. Among the several techniques used for the design of polymeric nanoparticles, nanoprecipitation has attracted great attention. This review focuses on the most outstanding contributions of nanotechnology in essential oils encapsulation via nanoprecipitation method. We emphasize the chemical composition of essential oils, the principle of polymeric nanoparticle preparation, the physicochemical properties of essential oils loaded nanoparticles and their current applications.

The Biofilms Structural Database

The Biofilms Structural Database (BSD) is a collection of structural, mutagenesis, kinetics, and inhibition data to understand the processes involved in biofilm formation. Presently, it includes curated information on 425 structures of proteins and enzymes involved in biofilm formation and development for 42 different bacteria. It is available at www.biofilms.biosim.pt.

Ultrasound-mediated therapies for the treatment of biofilms in chronic wounds: a review of present knowledge

Bacterial biofilms are an ever-growing concern for public health, featuring both inherited genetic resistance and a conferred innate tolerance to traditional antibiotic therapies. Consequently, there is a growing interest in novel methods of drug delivery, in order to increase the efficacy of antimicrobial agents. One such method is the use of acoustically activated microbubbles, which undergo volumetric oscillations and collapse upon exposure to an ultrasound field. This facilitates physical perturbation of the biofilm and provides the means to control drug delivery both temporally and spatially. In line with current literature in this area, this review offers a rounded argument for why ultrasound-responsive agents could be an integral part of advancing wound care. To achieve this, we will outline the development and clinical significance of biofilms in the context of chronic infections. We will then discuss current practices used in combating biofilms in chronic wounds and then critically evaluate the use of acoustically activated gas microbubbles as an emerging treatment modality. Moreover, we will introduce the novel concept of microbubbles carrying biologically active gases that may facilitate biofilm dispersal.

Host responses to mucosal biofilms in the lung and gut

The impact of the human microbiome on health and disease is of utmost importance and has been studied intensively in recent years. Microbes promote immune system development and are essential to the production and absorption of nutrients for the host but are also implicated in disease pathogenesis. Particularly, bacterial biofilms have long been recognized as contributors to chronic infections and diseases in humans. However, our understanding of how the host responds to the presence of biofilms, specifically the immune response to biofilms, and how this contributes to disease pathogenesis is limited. This review aims to highlight what is known about biofilm formation and in vivo models available for the biofilm study. We critique the contribution of biofilms to human diseases, focusing on the lung diseases, cystic fibrosis and chronic obstructive pulmonary disease, and the gut diseases, inflammatory bowel disease and colorectal cancer.

RETRACTED: Antibacterial and antibiofilm activity of ursolic acid against carbapenem-resistant Enterobacter cloacae

This article has been retracted: please see Elsevier Policy on Article Withdrawal (https://www.elsevier.com/about/our-business/policies/article-withdrawal). This article has been retracted at the request ofthe corresponding author and the editor-in-chief. The authors have notified the journal that Fig. 3E and 3F in this article was a duplicate image of Fig. 3C of the article published by Weidong Qian, Miao Liu, Yuting Fu, Ting Wang, Jianing Zhang, Min Yang, Zhaohuan Sun, Xiang Li, and Yongdong Li in Foodborne Pathogens and Disease 129 (2020) 528-534 https://www.liebertpub.com/doi/10.1089/fpd.2019.2751 and requested for retraction. The authors have subsequently admitted that Figs. 3A, 3D and 4B in this article were duplicated from Figs. 3A, 5A and 7B of the article published by Weidong Qian, Yuting Fu, Miao Liu, Ting Wang, Jianing Zhang, Min Yang, Zhaohuan Sun, Xiang Li and Yongdong Li in Antibiotics 8 (2019) 220 https://www.mdpi.com/2079-6382/8/4/220, which has been retracted https://www.mdpi.com/2079-6382/9/6/322. The authors have claimed that there were errors in the preparation of figures for three papers which had been submitted to multiple journals from August to October 2019. The authors have provided replacement images for Figs. 3 and 4 of this article, but these data did not resolve the concerns that call into question the reliability of the study findings. In light of these issues, the journal has decided to retract the article. The authors assert the findings, that ursolic acid exerted antibacterial activity against carbapenem-resistant Enterobacter cloacae, are nevertheless reliable.

Effect of Silver Nanoparticles on Biofilm Formation and EPS Production of Multidrug-Resistant Klebsiella pneumoniae

Antibiotic resistance against present antibiotics is rising at an alarming rate with need for discovery of advanced methods to treat infections caused by resistant pathogens. Silver nanoparticles are known to exhibit satisfactory antibacterial and antibiofilm activity against different pathogens. In the present study, the AgNPs were synthesized chemically and characterized by UV-Visible spectroscopy, scanning electron microscopy, and X-ray diffraction. Antibacterial activity against MDR K. pneumoniae strains was evaluated by agar diffusion and broth microdilution assay. Cellular protein leakage was determined by the Bradford assay. The effect of AgNPs on production on extracellular polymeric substances was evaluated. Biofilm formation was assessed by tube method qualitatively and quantitatively by the microtiter plate assay. The cytotoxic potential of AgNPs on HeLa cell lines was also determined. AgNPs exhibited an MIC of 62.5 and 125 μg/ml, while their MBC is 250 and 500 μg/ml. The production of extracellular polymeric substance decreased after AgNP treatment while cellular protein leakage increased due to higher rates of cellular membrane disruption by AgNPs. The percentage biofilm inhibition was evaluated to be 64% for K. pneumoniae strain MF953600 and 86% for MF953599 at AgNP concentration of 100 μg/ml. AgNPs were evaluated to be minimally cytotoxic and safe at concentrations of 15-120 μg/ml. The data evaluated by this study provided evidence of AgNPs being safe antibacterial and antibiofilm compounds against MDR K. pneumoniae.

Stable Fabrication of Zwitterionic Coating Based on Copper-Phenolic Networks on Contact Lens with Improved Surface Wettability and Broad-Spectrum Antimicrobial Activity

Ocular dryness and contact lens(CL)-related microbial keratitis (MK) are two major risks of wearing CLs. The development of multifunctional surface coating for CLs with excellent hydrating and antimicrobial properties is a practical strategy to improve the comfort of CL wearers and to prevent corneal infection. Here, we develop zwitterionic and antimicrobial metal-phenolic networks (MPNs) based on the coordination of copper ions (Cu^II) and the poly(carboxylbetaine-co-dopamine methacrylamide) copolymer (PCBDA), which can be easily one-step prepared onto CLs due to the near-universal adherent properties of catechol groups. The zwitterionic and antifouling carboxybetaine (CB) groups of the Cu^II-PCBDA coating can significantly increase the wettability of CLs and reduce their protein adsorptions, resulting in a lens surface that is more water retentive and with lower protein binding to prevent tear film evaporation and eye dryness. In addition, since the immobilized copper ions in the MPNs impart them with ion-mediated antimicrobial activity, the Cu^II-PCBDA coating exhibits a strong and broad-spectrum antimicrobial activity against MK related pathogenic microbes, including bacteria, such as Escherichia coli, Pseudomonas aeruginosa, and Staphylococcus aureus, and fungi, such as Candida albicans. Compared with a pristine CL, the Cu^II-PCBDA-coated CL effectively inhibited biofilm formation even after daily exposure to the above microbial environment for 14 days. Notably, the Cu^II-PCBDA coating developed in this study is not only biocompatible with 100% cell viability following direct contact with human corneal epithelial cells (HCECs) for 48 h but also maintains the optical clarity of the native CLs. Thus, the Cu^II-PCBDA coating has a great application potential for the development of a multifunctional surface coating for CLs for increased CL comfort and prevention of MK.

Optimization of ZnO Nanorods Growth on Polyetheresulfone Electrospun Mats to Promote Antibacterial Properties

Zinc oxide (ZnO) nanorods grown by chemical bath deposition (CBD) on the surface of polyetheresulfone (PES) electrospun fibers confer antimicrobial properties to the obtained hybrid inorganic–polymeric PES/ZnO mats. In particular, a decrement of bacteria colony forming units (CFU) is observed for both negative (Escherichia coli) and positive (Staphylococcus aureus and Staphylococcus epidermidis) Grams. Since antimicrobial action is strictly related to the quantity of ZnO present on surface, a CBD process optimization is performed to achieve the best results in terms of coverage uniformity and reproducibility. Scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) provide morphological and compositional analysis of PES/ZnO mats while thermogravimetric analysis (TGA) is useful to assess the best process conditions to guarantee the higher amount of ZnO with respect to PES scaffold. Biocidal action is associated to Zn²⁺ ion leaching in solution, easily indicated by UV–Vis measurement of metallation of free porphyrin layers deposited on glass.

BIPEP: Sequence-based Prediction of Biofilm Inhibitory Peptides Using a Combination of NMR and Physicochemical Descriptors

Biofilms are biological systems that are formed by a community of microorganisms in which microbial cells are connected on a surface within a self-produced matrix of an extracellular polymeric substance. On some occasions, microorganisms use biofilms to protect themselves against the harmful effects of the host body immune system and the surrounding environment, hence increasing their chances of survival against the various anti-microbial agents. Biofilms play a crucial role in medicine and industry because of the problems they cause. Designing agents that inhibit bacterial biofilm formation is very costly and takes too much time in the laboratory to be discovered and validated. Therefore, developing computational tools for the prediction of biofilm inhibitor peptides is inevitable and important. Here, we present a computational prediction tool to screen the vast number of peptide sequences and select potential candidate peptides for further lab experiments and validation. In this learning model, different feature vectors, extracted from the peptide primary structure, are exploited to learn patterns from the sequence of biofilm inhibitory peptides. Various classification algorithms including SVM, random forest, and k-nearest neighbor have been examined to evaluate their performance. Overall, our approach showed better prediction in comparison with other prediction methods. In this study, for the first time, we applied features extracted from NMR spectra of amino acids along with physicochemical features. Although each group of features showed good discrimination potential alone, we used a combination of features to enhance the performance of our method. Our prediction tool is freely available.

Antimicrobial activity and antibiotic synergy of a biphosphinic ruthenium complex against clinically relevant bacteria

The aim of this study was to investigate the antibacterial activity, antibiotic-associated synergy, and anti-biofilm activity of the ruthenium complex, cis-[RuCl₂ (dppb) (bqdi)]²⁺ (RuNN). RuNN exhibited antimicrobial activity against Gram-positive bacteria with minimum inhibitory concentration (MIC) values ranging from 15.6 to 62.5 µg ml^-1 and minimum bactericidal concentration (MBC) values ranging from 62.5 to 125 µg ml^-1. A synergistic effect against Staphylococcus spp. was observed when RuNN was combined with ampicillin, and the range of associated fractional inhibitory concentration index (FICI) values was 0.187 to 0.312. A time-kill curve indicated the bactericidal activity of RuNN in the first 1-5 h. In general, RuNN inhibited biofilm formation and disrupted mature biofilms. Furthermore, RuNN altered the cellular morphology of S. aureus biofilms. Further, RuNN did not cause hemolysis of erythrocytes. The results of this study provide evidence that RuNN is a novel therapeutic candidate to treat bacterial infections caused by Staphylococcus biofilms.

Bioactive Properties of Nanofibres Based on Concentrated Collagen Hydrolysate Loaded with Thyme and Oregano Essential Oils

This research aimed to obtain biocompatible and antimicrobial nanofibres based on concentrated collagen hydrolysate loaded with thyme or oregano essential oils as a natural alternative to synthesis products. The essential oils were successfully incorporated using electrospinning process into collagen resulting nanofibres with diameter from 471 nm to 580 nm and porous structure. The presence of essential oils in collagen nanofibre mats was confirmed by Attenuated Total Reflectance -Fourier Transform Infrared Spectroscopy (ATR-FTIR), Ultraviolet-visible spectroscopy (UV-VIS) and antimicrobial activity. Scanning Electron Microscopy with Energy Dispersive Spectroscopy analyses allowed evaluating the morphology and constituent elements of the nanofibre networks. Microbiological tests performed against Staphylococcus aureus, Escherichia coli, Pseudomonas aeruginosa and Candida albicans showed that the presence of essential oils supplemented the new collagen nanofibres with antimicrobial properties. The biocompatibility of collagen and collagen with essential oils was assessed by in vitro cultivation with NCTC clone 929 of fibroblastic cells and cell viability measurement. The results showed that the collagen and thyme or oregano oil composites have no cytotoxicity up to concentrations of 1000 μg·mL^-1 and 500 μg mL^-1, respectively. Optimization of electrospinning parameters has led to the obtaining of new collagen electrospun nanofibre mats loaded with essential oils with potential use for wound dressings, tissue engineering or protective clothing.

The Formation, Persistence, and Resistance to Disinfectant of the Erysipelothrix piscisicarius Biofilm

Erysipelothrix piscisicarius is an emergent pathogen in fish aquaculture, particularly in the ornamental fish trade. Very little is known on the biology of this pathogen; however, the recurrence of infection and disease outbreaks after removing the fish from a system and disinfecting the tank suggest its environmental persistence. Moreover, biofilm lifestyle in E. piscisicarius has been suspected but not previously shown. The purpose of this study was to investigate the formation of biofilms on an abiotic surface in Erysipelothrix spp. We used hydroxyapatite-coated plastic pegs to demonstrate the attachment, growth, and persistence of E. piscisicarius on abiotic surfaces in both fresh and marine environments and to investigate the susceptibility of this pathogen to different disinfectants that are used in the aquaculture industry. E. piscisicarius formed biofilms that persisted significantly longer than planktonic cells did in both freshwater and saltwater over a period of 120 h (P = 0.004). The biofilms were also more resistant to disinfectants than the planktonic cells were. Hydrogen peroxide was the most effective disinfectant against E. piscisicarius, and it eradicated the biofilms and planktonic cells at the recommended concentrations. In contrast, Virkon and bleach were able to eradicate only the planktonic cells. This information should be taken into consideration when developing biosecurity protocols in aquaculture systems, aquariums, and private collections.

Dibasic Derivatives of Phenylcarbamic Acid as Prospective Antibacterial Agents Interacting with Cytoplasmic Membrane

1-[2-[({[2-/3-(Alkoxy)phenyl]amino}carbonyl)oxy]-3-(dipropylammonio)propyl]pyrrolidinium/azepan- ium oxalates or dichlorides (alkoxy = butoxy to heptyloxy) were recently described as very promising antimycobacterial agents. These compounds were tested in vitro against Staphylococcus aureus ATCC 29213, Enterococcus faecalis ATCC 29212 (reference and control strains), three methicillin-resistant isolates of S. aureus, and three isolates of vancomycin-resistant E. faecalis. 1-[3-(Dipropylammonio)-2-({[3-(pentyloxy-/hexyloxy-/heptyloxy)phenyl]carbamoyl}oxy)propyl]pyrrolidinium dichlorides showed high activity against staphylococci and enterococci comparable with or higher than that of used controls (clinically used antibiotics and antiseptics). The screening of the cytotoxicity of the compounds as well as the used controls was performed using human monocytic leukemia cells. IC50 values of the most effective compounds ranged from ca. 3.5 to 6.3 µM, thus, it can be stated that the antimicrobial effect is closely connected with their cytotoxicity. The antibacterial activity is based on the surface activity of the compounds that are influenced by the length of their alkoxy side chain, the size of the azacyclic system, and hydro-lipophilic properties, as proven by in vitro experiments and chemometric principal component analyses. Synergistic studies showed the increased activity of oxacillin, gentamicin, and vancomycin, which could be explained by the direct activity of the compounds against the bacterial cell wall. All these compounds demonstrate excellent antibiofilm activity, when they inhibit and disrupt the biofilm of S. aureus in concentrations close to minimum inhibitory concentrations against planktonic cells. Expected interactions of the compounds with the cytoplasmic membrane are proven by in vitro crystal violet uptake assays.