Microbial biofilms: biosurfactants as antibiofilm agents

Active-bromide and surfactant synergy for enhanced microfouling control

Biofilms are structured microbial communities encased in a matrix of self-produced extracellular polymeric substance (EPS) and pose significant challenges in various industrial cooling systems. A nuclear power plant uses a biocide active-bromide for control of biological growth in its condenser cooling system. This study is aimed at evaluating the anti-bacterial and anti-biofilm efficacy of active-bromide against planktonic and biofilm-forming bacteria that are commonly encountered in seawater cooling systems. The results demonstrated that active-bromide at the concentration used at the power plant (1 ppm) exhibited minimal killing activity against Pseudomonas aeruginosa planktonic cells. The bacterial cell surface hydrophobicity assay using Staphylococcus aureus and P. aeruginosa indicated that Triton-X 100 significantly decreased the hydrophobicity of planktonic cells, enhancing the susceptibility of the cells to active-bromide. Biofilm inhibition assays revealed limited efficacy of active-bromide at 1 ppm concentration, but significant inhibition at 5 ppm and 10 ppm. However, the addition of a surfactant, Triton-X 100, in combination with 1 ppm active-bromide displayed a synergistic effect, leading to significant biofilm dispersal of pre-formed P. aeruginosa biofilms. This observation was substantiated by epifluorescence microscopy using a live/dead bacterial assay that showed the combination treatment resulted in extensive cell death within the biofilm, as indicated by a marked increase in red fluorescence, compared to treatments with either agent alone. These findings suggest that active bromide alone may be insufficient for microfouling control in the seawater-based condenser cooling system of the power plant. Including a biocompatible surfactant that disrupts established biofilms (microfouling) can significantly improve the efficacy of active bromide treatment.

Sophorolipid: An Effective Biomolecule for Targeting Microbial Biofilms

Biofilms are microbial aggregates encased in a matrix that is attached to biological or nonbiological surfaces and constitute serious problems in food, medical, and marine industries and can have major negative effects on both health and the economy. Biofilm's complex microbial community provides a resistant environment that is difficult to eradicate and is extremely resilient to antibiotics and sanitizers. There are various conventional techniques for combating biofilms, including, chemical removal, physical or mechanical removal, use of antibiotics and disinfectants to destroy biofilm producing organisms. In contrast to free living planktonic cells, biofilms are very resistant to these methods. Hence, new strategies that differ from traditional approaches are urgently required. Microbial world offers a wide range of effective "green" compounds such as biosurfactants. They outperform synthetic surfactants in terms of biodegradability, superior stabilization, and reduced toxicity concerns. They also have better antiadhesive and anti-biofilm capabilities which can be used to treat biofilm-related problems. Sophorolipids (SLs) are a major type of biosurfactants that have gained immense interest in the healthcare industries because of their antiadhesive and anti-biofilm properties. Sophorolipids may therefore prove to be attractive substances that can be used in biomedical applications as adjuvant to other antibiotics against some infections through growth inhibition and/or biofilm disruption.

Enhanced antibacterial efficacy: rapid analysis of silver-decorated azithromycin-infused Soluplus® nanoparticles against E. coli and S. epidermidis biofilms

The escalating threat of antibiotic-resistant bacterial biofilms necessitates innovative antimicrobial strategies. This study introduces silver-decorated azithromycin-infused Soluplus® nanoparticles (Ag-AZI-Sol NPs) synthesized via a controlled emulsion diffusion method to ensure sustained release of antimicrobial silver ions for over six hours-a critical factor for continuous antibacterial efficacy. The efficacy of these nanoparticles was evaluated against biofilms formed by Escherichia coli (E. coli) and Staphylococcus epidermidis (S. epidermidis), pathogens that cause hospital-acquired infections. Concentrations of 5 and 10 μg mL-1 of Ag-AZI-Sol NPs induced significant morphological changes within the biofilms, disrupting the bacterial extracellular matrix as observed using scanning electron microscopy (SEM). This disruption peaked between two and six hours, coinciding with damage to bacterial cells by the silver ions. Antibacterial assay measurements confirmed a significant reduction in the growth rate among the Ag-AZI-Sol NP-treated bacteria compared with controls. Electrochemical analysis using laser-induced graphene (LIG) and chronoamperometry revealed a decline in current, indicating an effective antibacterial effect. This innovative biosensing technique makes use of the high conductivity and surface area of LIG to detect changes in bacterial activity quickly and sensitively. Our findings highlight the potent microbicidal properties of Ag-AZI-Sol NPs and suggest diverse applications from food processing to medical device coatings.

Promising Application, Efficient Production, and Genetic Basis of Mannosylerythritol Lipids

Mannosylerythritol lipids (MELs) are a class of glycolipids that have been receiving increasing attention in recent years due to their diverse biological activities. MELs are produced by certain fungi and display a range of bioactivities, making them attractive candidates for various applications in medicine, agriculture, and biotechnology. Despite their remarkable qualities, industrial-scale production of MELs remains a challenge for fungal strains. Excellent fungal strains and fermentation processes are essential for the efficient production of MELs, so efforts have been made to improve the fermentation yield by screening high-yielding strains, optimizing fermentation conditions, and improving product purification processes. The availability of the genome sequence is pivotal for elucidating the genetic basis of fungal MEL biosynthesis. This review aims to shed light on the applications of MELs and provide insights into the genetic basis for efficient MEL production. Additionally, this review offers new perspectives on optimizing MEL production, contributing to the advancement of sustainable biosurfactant technologies.

Lipopeptide biosurfactant as a potential root canal irrigation agent: Antimicrobial and anti-biofilm evaluation

OBJECTIVES

Lipopeptide Biosurfactant (LB) is a bacteria derived compound able to reduce surface tension between water and hydrophobic substances and exhibit antimicrobial and anti-biofilm properties. This study aimed to investigate the antimicrobial and anti-biofilm effect of a Lipopeptide Biosurfactant (LB) on Enterococcus faecalis, and its potential use in root canal treatment, either as a standalone irrigation solution or in conjunction with sodium hypochlorite (NaOCl).

METHODS

LB was extracted from Bacillus clausii isolate and the dry extract was diluted in deionized water. The antimicrobial effect of LB against planktonic E. faecalis was evaluated by determining the Minimal Inhibitory Concentration (MIC50). The anti-biofilm effect was evaluated by Minimal Biofilm Inhibitory Concentration (MBIC50) and Minimal Biofilm Eradication Concentration (MBEC50) assays on biofilm grown on dentin specimen surface. To evaluate the effectiveness of LB as a single irrigation solution and as a pre-irrigation prior to NaOCl, live and dead bacterial cells were quantified using Confocal Laser Scanning Microscopy (CLSM), and cell biomass was assessed.

RESULTS

LB exhibited an MIC50 and MBIC50 of 100 ppm, with an MBEC50 of 1000 ppm, resulting in 52.94 % biofilm inhibition and 60.95 % biofilm eradication on dentin specimens. The effectiveness was concentration-dependent, at 500 ppm, LB demonstrated comparable antimicrobial efficacy to 2.5 % NaOCl. Pre-irrigation with LB resulted in lower biofilm biomass compared to NaOCl alone.

CONCLUSION

Pre-irrigation with LB enhanced the antimicrobial effect when followed by NaOCl irrigation. Consequently, LB shows promise as both a standalone root canal irrigation solution and as an adjunct to NaOCl in root canal treatment.

CLINICAL SIGNIFICANCE

The study highlights the potential of Lipopeptide Biosurfactant (LB) as an environmentally friendly irrigation solution for root canal treatment, demonstrating potent antimicrobial and anti-biofilm properties against Enterococcus faecalis. LB exhibits concentration-dependent efficacy comparable to 2.5 % NaOCl and can be used as a standalone irrigation solution or in conjunction with NaOCl.

Comprehensive Review on the Use of Biocides in Microbiologically Influenced Corrosion

A microbiologically influenced corrosion (MIC) causes huge economic losses and serious environmental damage every year. The prevention and control measures for MIC mainly include physical, chemical, and biological methods. Among them, biocide application is the most cost-effective method. Although various biocides have their own advantages in preventing and treating MIC, most biocides have the problem of polluting the environment and increasing microorganism resistance. Therefore, it has stimulated the exploration of continuously developing new environmentally friendly and efficient biocides. In this review, the application advantages and research progress of various biocides used to prevent and control MIC are discussed. Also, this review provides a resource for the research and rational use of biocides regarding MIC mitigation and prevention.

Evaluation of the Antibacterial Effect of Aurone-Derived Triazoles on Staphylococcus aureus

Infections caused by antibiotic-resistant bacteria continue to pose a significant public health threat despite their overall decreasing numbers in the last two decades. One group of compounds fundamental to the search for new agents is low-cost natural products. In this study, we explored a group of newly synthesized novel aurone-derived triazole compounds to identify those with pharmaceutical potential as inhibitors of antibiotic-resistant Staphylococcus aureus. Using the broth microdilution method, antibacterial activities against methicillin-resistant S. aureus ATCC 43300 (MRSA) and methicillin-sensitive S. aureus ATCC 29213 (MSSA) were identified for four aurone-derived triazole compounds, AT106, AT116, AT125, and AT137, using the half-maximal inhibitory concentrations for the bacteria (IC50) and mammalian cell lines (CC50). Compounds AT125 and AT137 were identified to have pharmaceutical potential as the IC50 values against MRSA were 5.412 µM and 3.870 µM, whereas the CC50 values measured on HepG2 cells were 50.57 µM and 39.81 µM, respectively, resulting in selectivity indexes (SI) > 10. Compounds AT106 and AT116 were also selected for further study. IC50 values for these compounds were 5.439 µM and 3.178 µM, and the CC50 values were 60.33 µM and 50.87 µM, respectively; however, SI values > 10 were for MSSA only. Furthermore, none of the selected compounds showed significant hemolytic activity for human erythrocytes. We also tested the four compounds against S. aureus biofilms. Although AT116 and AT125 successfully disrupted MSSA biofilms, there was no measurable potency against MRSA biofilms. Checkerboard antibiotic assays to identify inhibitory mechanisms for these compounds indicated activity against bacterial cell membranes and cell walls, supporting the pharmaceutical potential for aurone-derived triazoles against antibiotic-resistant bacteria. Examining structure-activity relationships between the four compounds in this study and other aurone-derived triazoles in our library suggest that substitution with a halogen on either the salicyl ring or triazole aryl group along with triazoles having nitrile groups improves anti-Staphylococcal activity with the location of the functionality being very important.

Pharmacodynamic Model of the Dynamic Response of Pseudomonas aeruginosa Biofilms to Antibacterial Treatments

Accurate pharmacokinetic-pharmacodynamic (PK-PD) models of biofilm treatment could be used to guide formulation and administration strategies to better control bacterial lung infections. To this end, we developed a detailed pharmacodynamic model of P. aeruginosa treatment with the front-line antibiotics, tobramycin and colistin, and validated it on a detailed dataset of killing dynamics. A compartmental model structure was developed in which the key features are the diffusion of the drug through a boundary layer to the bacteria, concentration-dependent interactions with bacteria, and the passage of the bacteria through successive transit states before death. The number of transit states employed was greater for tobramycin, which is a ribosomal inhibitor, than for colistin, which disrupts bacterial membranes. For both drugs, the experimentally observed delay in the killing of bacteria following drug exposure was consistent with the sum of the diffusion time and the time for passage through the transit states. For each drug, the PD model with a single set of parameters described data across a ten-fold range of concentrations and for both continuous and transient exposure protocols, as well as for combined drug treatments. The ability to predict drug response over a range of administration protocols allows this PD model to be integrated with PK descriptions to describe in vivo antibiotic response dynamics and to predict drug delivery strategies for the improved control of bacterial lung infections.

Biosurfactant from Nile Papyrus endophyte with potential antibiofilm activity against global clones of Acinetobacter baumannii

Acinetobacter baumannii is a leading cause of biofilm-associated infections, particularly catheter-related bloodstream infections (CRBSIs) that are mostly recalcitrant to antimicrobial therapy. One approach to reducing the burden of CRBSIs is inhibiting biofilm formation on catheters. Owing to their prodigious microbial diversity, bacterial endophytes might be a valuable source of biosurfactants, which are known for their great capacity to disperse microbial biofilms. With this in mind, our study aimed to screen bacterial endophytes from plants growing on the banks of the River Nile for the production of powerful biosurfactants capable of reducing the ability of A. baumannii to form biofilms on central venous catheters (CVCs). This was tested on multidrug- and extensive drug-resistant (M/XDR) clinical isolates of A. baumannii that belong to high-risk global clones and on a standard strain of A. baumannii ATCC 19606. The drop collapse and oil dispersion assays were employed in screening the cell-free supernatants (CFS) of all endophytes for biosurfactant activity. Of the 44 bacterial endophytes recovered from 10 plants, the CFS of Bacillus amyloliquefaciens Cp24, isolated from Cyperus papyrus, showed the highest biosurfactant activity. The crude biosurfactant extract of Cp24 showed potent antibacterial activity with minimum inhibitory concentrations (MICs) ranging from 0.78 to 1.56 mg/ml. It also showed significant antibiofilm activity (p-value<0.01). Sub-MICs of the extract could reduce biofilm formation by up to 89.59%, while up to 87.3% of the preformed biofilms were eradicated by the MIC. A significant reduction in biofilm formation on CVCs impregnated with sub-MIC of the extract was demonstrated by CV assay and further confirmed by scanning electron microscopy. This was associated with three log₁₀ reductions in adhered bacteria in the viable count assay. GC-MS analysis of the crude biosurfactant extract revealed the presence of several compounds, such as saturated, unsaturated, and epoxy fatty acids, cyclopeptides, and 3-Benzyl-hexahydro-pyrrolo [1, 2-a] pyrazine-1,4-dione, potentially implicated in the potent biosurfactant and antibiofilm activities. In the present study, we report the isolation of a B. amyloliquefaciens endophyte from the plant C. papyrus that produces a biosurfactant with potent antibiofilm activity against MDR/XDR global clones of A. baumannii. The impregnation of CVCs with the biosurfactant was demonstrated to reduce biofilms and, hence, proposed as a potential strategy for reducing CRBSIs.

Artificial intelligence-based optimization for chitosan nanoparticles biosynthesis, characterization and in‑vitro assessment of its anti-biofilm potentiality

Chitosan nanoparticles (CNPs) are promising biopolymeric nanoparticles with excellent physicochemical, antimicrobial, and biological properties. CNPs have a wide range of applications due to their unique characteristics, including plant growth promotion and protection, drug delivery, antimicrobials, and encapsulation. The current study describes an alternative, biologically-based strategy for CNPs biosynthesis using Olea europaea leaves extract. Face centered central composite design (FCCCD), with 50 experiments was used for optimization of CNPs biosynthesis. The artificial neural network (ANN) was employed for analyzing, validating, and predicting CNPs biosynthesis using Olea europaea leaves extract. Using the desirability function, the optimum conditions for maximum CNPs biosynthesis were determined theoretically and verified experimentally. The highest experimental yield of CNPs (21.15 mg CNPs/mL) was obtained using chitosan solution of 1%, leaves extract solution of 100%, initial pH 4.47, and incubation time of 60 min at 53.83°C. The SEM and TEM images revealed that CNPs had a spherical form and varied in size between 6.91 and 11.14 nm. X-ray diffraction demonstrates the crystalline nature of CNPs. The surface of the CNPs is positively charged, having a Zeta potential of 33.1 mV. FTIR analysis revealed various functional groups including C-H, C-O, CONH2, NH2, C-OH and C-O-C. The thermogravimetric investigation indicated that CNPs are thermally stable. The CNPs were able to suppress biofilm formation by P. aeruginosa, S. aureus and C. albicans at concentrations ranging from 10 to 1500 µg/mL in a dose-dependent manner. Inhibition of biofilm formation was associated with suppression of metabolic activity, protein/exopolysaccharide moieties, and hydrophobicity of biofilm encased cells (r ˃ 0.9, P = 0.00). Due to their small size, in the range of 6.91 to 11.14 nm, CNPs produced using Olea europaea leaves extract are promising for applications in the medical and pharmaceutical industries, in addition to their potential application in controlling multidrug-resistant microorganisms, especially those associated with post COVID-19 pneumonia in immunosuppressed patients.

Production of Biosurfactant Using Bacillus subtilis Natto Fermentation

Biosurfactants are microbial amphiphiles produced as primary metabolites by varieties of microorganisms. They are preferred over chemically derived surfactants owing to their intrinsic properties, such as superior environmental compatibility, biodegradability, anti-inflammatory and antimicrobial activity, and higher tolerance towards extreme environmental conditions such as temperature, salinity, and pH levels. However, commercial production of biosurfactants is still lacking. The main reason for this is the low yields obtained from fermentation processes, which causes them to be unable to compete compared to chemical surfactants. The present study conducted a one-factor-at-a-time (OFAT) analysis on fermentation conditions to enhance biosurfactant yield from a probiotic strain, Bacillus subtilis Natto. The fermentation was conducted by varying parameters such as nitrogen source, vegetable oils, inoculum size, amino acids, and pH of the fermentation medium. Results showed a significant improvement of 45% in biosurfactant production from B. subtilis Natto when the initial pH of the fermentation medium was adjusted to pH 6.8, urea as the nitrogen source, inoculum size of 6% v/v and the addition of palm olein at a concentration of 2% v/v as a substrate in the fermentation medium.

Unravelling the sponge microbiome as a promising source of biosurfactants

Microbial surfactants are particularly useful in bioremediation and heavy metal removal from soil and aquatic environments, amongst other highly valued uses in different economic and biomedical sectors. Marine sponge-associated bacteria are well-known producers of bioactive compounds with a wide array of potential applications. However, little progress has been made on investigating biosurfactants produced by these bacteria, especially when compared with other groups of biologically active molecules harnessed from the sponge microbiome. Using a thorough literature search in eight databases, the purpose of the review was to compile the current knowledge on biosurfactants from sponge-associated bacteria, with a focus on their relevant biotechnological applications. From the publications between the years 1995 and 2021, lipopeptides and glycolipids were the most identified chemical classes of biosurfactants. Firmicutes was the dominant phylum of biosurfactant-producing strains, followed by Actinobacteria and Proteobacteria. Bioremediation led as the most promising application field for the studied surface-active molecules in sponge-derived bacteria, despite the reports endorsed their use as antimicrobial and antibiofilm agents. Finally, we appoint some key strategies to instigate the research appetite on the isolation and characterization of novel biosurfactants from the poriferan microbiome.

Antibiofilm Activity of Weissella spp. and Bacillus coagulans Isolated from Equine Skin against Staphylococcus aureus

The aim of this study was to evaluate the antimicrobial and antibiofilm activity of Weissella cibaria, Weissella hellenica and Bacillus coagulans, isolated from equine skin, against biofilm-forming Staphylococcus aureus CCM 4223 and clinical isolate methicillin-resistant S. aureus (MRSA). Non-neutralized cell-free supernatants (nnCFS) of tested skin isolates completely inhibited the growth and biofilm formation of S. aureus strains and caused dispersion of the 24 h preformed biofilm in the range of 21-90%. The majority of the pH-neutralized cell-free supernatants (nCFS) of skin isolates inhibited the biofilm formation of both S. aureus strains in the range of 20-100%. The dispersion activity of B. coagulans nCFS ranged from 17 to 77% and was significantly lower than that of nnCFS, except for B. coagulans 3T27 against S. aureus CCM 4223. Changes in the growth of S. aureus CCM 4223 in the presence of catalase- or trypsin-treated W. hellenica 4/2D23 and W. cibaria 4/8D37 nCFS indicated the role of peroxides and/or bacteriocin in their antimicrobial activities. For the first time, the presence of the fenD gene, associated with biosurfactants production, was detected in B. coagulans. The results of this study showed that selected isolates may have the potential for the prevention and treatment of biofilm-forming S. aureus infections.

Anti-oxidative property of xylolipid produced by Lactococcus lactis LNH70 and its potential use as fruit juice preservative

In the present study, 20 lactic acid bacteria (LAB) were isolated from different fruit juices, milk, and milk products. Based on preliminary screening methods like emulsification index, oil displacement method, hemolysis, and reduction in surface tension, strain LNH70 was selected for further studies. Further, it was evaluated for preliminary probiotic characteristics, identified by 16 s rRNA sequencing as Lactococcus lactis, submitted to NCBI, and an accession number was obtained (MH174454). In addition, LNH70 was found to tolerate over wide range of temperatures (10-45 °C), pH (3-10), NaCl (up to 9%), bile (0.7%), and phenol (0.1%) concentrations. Further, optimization studies at flask level revealed that lactose as carbon source, peptone as organic nitrogen, and inorganic nitrogen (ammonium sulfate) enhanced biosurfactant production. Chemical composition of purified biosurfactant obtained from LNH70 was characterized by various physico-chemical analytical techniques and identified as xylolipid. Xylolipid biosurfactant exhibited anti-adhesion activity against food borne pathogens in in vitro conditions. Its anti-oxidative property by 1, 1-diphenyl-2-picrylhydrazyl (DPPH), 2, 2'-azino-bis (3-ethylbenzothiazoline-6-sulphonic acid (ABTS), and ferric reducing antioxidant power (FRAP) radical scavenging activity was found in range of 60.76 ± 0.5 to 83.50 ± 0.73%. Furthermore, xylolipid (0.05, 0.1, 0.3 mg/mL) when used for its potential as orange and pineapple juices preservation revealed miniature changes in the physico-chemical parameters evaluated in this study. However, the microbial population slightly lowered when xylolipid was used at 0.3 mg/mL after 5th day. Hence, this study supports the potential use of biosurfactant from L. lactis for its application as food preservative.

CATASAN Is a New Anti-Biofilm Agent Produced by the Marine Antarctic Bacterium Psychrobacter sp. TAE2020

The development of new approaches to prevent microbial surface adhesion and biofilm formation is an emerging need following the growing understanding of the impact of biofilm-related infections on human health. Staphylococcus epidermidis, with its ability to form biofilm and colonize biomaterials, represents the most frequent causative agent involved in infections of medical devices. In the research of new anti-biofilm agents against S. epidermidis biofilm, Antarctic marine bacteria represent an untapped reservoir of biodiversity. In the present study, the attention was focused on Psychrobacter sp. TAE2020, an Antarctic marine bacterium that produces molecules able to impair the initial attachment of S. epidermidis strains to the polystyrene surface. The setup of suitable purification protocols allowed the identification by NMR spectroscopy and LC-MS/MS analysis of a protein-polysaccharide complex named CATASAN. This complex proved to be a very effective anti-biofilm agent. Indeed, it not only interferes with cell surface attachment, but also prevents biofilm formation and affects the mature biofilm matrix structure of S. epidermidis. Moreover, CATASAN is endowed with a good emulsification activity in a wide range of pH and temperature. Therefore, its use can be easily extended to different biotechnological applications.

Inhibition of heterotrophic bacterial biofilm in the soil ferrosphere by Streptomyces spp. and Bacillus velezensis

The soil microbiome is involved in the processes of microbial corrosion, in particular, by the formation of biofilm. It has been proposed that an environmentally friendly solution to this corrosion might be through biological control. Bacillus velezensis NUChC C2b, Streptomyces gardneri ChNPU F3 and S. canus NUChC F2 were investigated as potentially 'green' biocides to prevent attachment to glass as a model surface and the formation of heterotrophic bacterial biofilm which participates in the corrosion process. Results showed high antagonistic and antibiofilm properties of S. gardneri ChNPU F3; which may be related to the formation of secondary antimicrobial metabolites by this strain. B. velezensis NUChC C2b and S. gardneri ChNPU F3 could be incorporated into green biocides - as components of antibiofilm agents that will protect material from bacterial corrosion or as agents that will prevent historical heritage damage.

Synthetic and biological surfactant effects on freshwater biofilm community composition and metabolic activity

Surfactants are used to control microbial biofilms in industrial and medical settings. Their known toxicity on aquatic biota, and their longevity in the environment, has encouraged research on biodegradable alternatives such as rhamnolipids. While previous research has investigated the effects of biological surfactants on single species biofilms, there remains a lack of information regarding the effects of synthetic and biological surfactants in freshwater ecosystems. We conducted a mesocosm experiment to test how the surfactant sodium dodecyl sulfate (SDS) and the biological surfactant rhamnolipid altered community composition and metabolic activity of freshwater biofilms. Biofilms were cultured in the flumes using lake water from Lake Lunz in Austria, under high (300 ppm) and low (150 ppm) concentrations of either surfactant over a four-week period. Our results show that both surfactants significantly affected microbial diversity. Up to 36% of microbial operational taxonomic units were lost after surfactant exposure. Rhamnolipid exposure also increased the production of the extracellular enzymes, leucine aminopeptidase, and glucosidase, while SDS exposure reduced leucine aminopeptidase and glucosidase. This study demonstrates that exposure of freshwater biofilms to chemical and biological surfactants caused a reduction of microbial diversity and changes in biofilm metabolism, exemplified by shifts in extracellular enzyme activities. KEY POINTS: • Microbial biofilm diversity decreased significantly after surfactant exposure. • Exposure to either surfactant altered extracellular enzyme activity. • Overall metabolic activity was not altered, suggesting functional redundancy.

Bacillus amyloliquefaciens CU33 fermented feather meal-soybean meal product improves the intestinal morphology to promote the growth performance of broilers

This study is aimed to select optimum keratin degradation ability from Bacillus strains for feather meal-soybean meal fermentation, and favorably water content for the strain during fermentation of feather meal-soybean meal, and finally investigate the effects of the fermented feather meal-soybean meal product (FFSMP) on growth performance, carcass trait, clinical blood biochemistry, and intestinal morphology of broilers. Thirty-six bacteria strains from soil, sewage pool, and feather waste were screened and selected Bacillus subtilis var. natto N21 (N21), B. subtilis CU14 (CU14), and B. amyloliquefaciens CU33 (CU33) with better keratinase activity and feather-degrading rate. The result of trial 1 showed that the FFSMP produced by CU33 had the optimum physiochemical characterizations, amino acid composition and feeding performance for broilers. Hence the effects of water content (45, 50, 55, and 60%) on FFMSP fermentation of CU33 were investigated in trial 2. Result showed that pH value, counts of Bacillus-like bacteria, γ-PGA, viscosity, surfactin yield and odor all significantly increased according to the water content (P < 0.05). The protease activity reached significantly highest in the 55% and 60% water content groups (P < 0.01). The broilers performance of 55% and 60% water content group were significantly higher than control group (P < 0.05) in weight gain (WG), feed intake (b) at 0 to 21-d-old and the WG, feed conversion ratio (FCR), and production efficiency factor at 0 to 35-d-old, and could reach the similar growth performance as fish meal group (P > 0.05). The fermentation groups significantly decreased urea nitrogen (P < 0.05) and increased creatinine (P < 0.05) in the blood. The fermentation groups also significantly decreased the crypt depth in the duodenum (P < 0.05) and increased villus height to crypt depth ratio of the duodenum (P < 0.05). In conclusion, CU33 shows the best degradation rate for feather and keratinase activity, and the FFSMP with a water content of 50% to 60% during fermentation is suggested. Diets supplemented with 5% FFSMP can promote the growth of broilers by improving the morphology of the duodenum and achieve the feeding effect of high-quality fish meal.

Biofilms as a microbial hazard in the food industry: A scoping review

Biofilms pose a serious public health hazard with a significant economic impact on the food industry. The present scoping review is designed to analyze the literature published during 2001-2020 on biofilm formation of microbes, their detection methods, and association with antimicrobial resistance (if any). The peer-reviewed articles retrieved from 04 electronic databases were assessed using PRISMA-ScR guidelines. From the 978 preliminary search results, a total of 88 publications were included in the study. On analysis, the commonly isolated pathogens were Listeria monocytogenes, Staphylococcus aureus, Salmonella spp., Escherichia coli, Bacillus spp., Vibrio spp., Campylobacter jejuni and Clostridium perfringens. The biofilm-forming ability of microbes was found to be influenced by various factors such as attachment surfaces, temperature, presence of other species, nutrient availability etc. A total of 18 studies characterized the biofilm-forming genes, particularly for S. aureus, Salmonella spp., and E. coli. In most studies, polystyrene plate and/or stainless-steel coupons were used for biofilm formation, and the detection was carried out by crystal violet assays and/or by plate counting method. The strain-specific significant differences in biofilm formation were observed in many studies, and few studies carried out analysis of multi-species biofilms. The association between biofilm formation and antimicrobial resistance wasn't clearly defined. Further, viable but non-culturable (VBNC) form of the foodborne pathogens is posing an unseen (by conventional cultivation techniques) but potent threat food safety. The present review recommends the need for carrying out systematic surveys and risk analysis of biofilms in food chain to highlight the evidence-based public health concerns, especially in regions where microbiological food hazards are quite prevalent.

Complete Genome Sequences of One Salt-Tolerant and Petroleum Hydrocarbon-Emulsifying Terribacillus saccharophilus Strain ZY-1

Salt tolerance is one of the most important problems in the field of environmental governance and restoration. Among the various sources of factors, except temperature, salinity is a key factor that interrupts bacterial growth significantly. In this regard, constant efforts are made for the development of salt-tolerant strains, but few strains with salt tolerance, such as Terribacillus saccharophilus, were found, and there are still few relevant reports about their salt tolerance from complete genomic analysis. Furthermore, with the development of the economy, environmental pollution caused by oil exploitation has attracted much attention, so it is crucial to find the bacteria from T. saccharophilus which could degrade petroleum hydrocarbon even under high-salt conditions. Herein, one T. saccharophilus strain named ZY-1 with salt tolerance was isolated by increasing the salinity on LB medium step by step with reservoir water as the bacterial source. Its complete genome was sequenced, which was the first report of the complete genome for T. saccharophilus species with petroleum hydrocarbon degradation and emulsifying properties. In addition, its genome sequences were compared with the other five strains that are from the same genus level. The results indicated that there really exist some differences among them. In addition, some characteristics were studied. The salt-tolerant strain ZY-1 developed in this study and its emulsification and degradation performance of petroleum hydrocarbons were studied, which is expected to widely broaden the research scope of petroleum hydrocarbon-degrading bacteria in the oil field environment even in the extreme environment. The experiments verified that ZY-1 could significantly grow not only in the salt field but also in the oil field environment. It also demonstrated that the developed salt-tolerant strain can be applied in the petroleum hydrocarbon pollution field for bioremediation. In addition, we expect that the identified variants which occurred specifically in the high-salt strain will enhance the molecular biological understanding and be broadly applied to the biological engineering field.

Metabolomics and Genomics Approach for the Discovery of Serrawettin W2 Lipopeptides from Serratia marcescens NP2

A metabolomics/peptidomics and genomics approach, using UPLC-MS^E, molecular networking, and genome mining, was used to describe the serrawettin W2 lipopeptide family produced by Serratia marcescens NP2. Seven known serrawettin W2 analogues were structurally elucidated along with 17 new analogues, which varied based on the first (fatty acyl length of C₈, C₁₀, C₁₂, or C_12:1), fifth (Phe, Tyr, Trp, or Leu/Ile), and sixth (Leu, Ile, or Val) residues. Tandem MS results suggested that the previously classified serrawettin W3 may be an analogue of serrawettin W2, with a putative structure of cyclo(C₁₀H₁₈O₂-Leu-Ser-Thr-Leu/Ile-Val). Chiral phase amino acid analysis enabled the distinction between l/d-Leu and l-Ile residues within nine purified compounds. ¹H and ¹³C NMR analyses confirmed the structures of four purified new analogues. Additionally, genome mining was conducted using Serratia genome sequences available on the NCBI database to identify the swrA gene using the antiSMASH software. NRPSpredictor2 predicted the specificity score of the adenylation-domain within swrA with 100% for the first, second, and third modules (Leu-Ser-Thr), 60-70% for the fourth module (Phe/Trp/Tyr/Val), and 70% for the fifth module (Val/Leu/Ile), confirming MS^E data. Finally, antibacterial activity was observed for compounds 6 and 11 against a clinical Enterococcus faecium strain.

Lactic acid bacteria and their bacteriocins: new potential weapons in the fight against methicillin-resistant Staphylococcus aureus

Alternative solutions are eminently needed to combat the escalating number of infections caused by methicillin-resistant Staphylococcus aureus (MRSA). Bacteriocins produced by lactic acid bacteria are promising candidates for next-generation antibiotics. Studies have found that these stable and nontoxic ribosomally synthesized antimicrobial peptides exhibit significant potency against other bacteria, including antibiotic-resistant strains. Here the authors review previous studies on bacteriocins that have been effectively employed to manage MRSA infections. The authors' review focuses on the beneficial traits of bacteriocins for further application as templates for the design of novel drugs. Treatments that combine bacteriocins with other antimicrobials to combat pervasive MRSA infections are also highlighted. In short, future studies should focus on the pharmacodynamics and pharmacokinetics of bacteriocins-antimicrobials to understand their interactions, as this aspect would likely determine their efficacy in MRSA inhibition.

Biofilm Formation by Pathogenic Bacteria: Applying a Staphylococcus aureus Model to Appraise Potential Targets for Therapeutic Intervention

Carried in the nasal passages by up to 30% of humans, Staphylococcus aureus is recognized to be a successful opportunistic pathogen. It is a frequent cause of infections of the upper respiratory tract, including sinusitis, and of the skin, typically abscesses, as well as of food poisoning and medical device contamination. The antimicrobial resistance of such, often chronic, health conditions is underpinned by the unique structure of bacterial biofilm, which is the focus of increasing research to try to overcome this serious public health challenge. Due to the protective barrier of an exopolysaccharide matrix, bacteria that are embedded within biofilm are highly resistant both to an infected individual’s immune response and to any treating antibiotics. An in-depth appraisal of the stepwise progression of biofilm formation by S. aureus, used as a model infection for all cases of bacterial antibiotic resistance, has enhanced understanding of this complicated microscopic structure and served to highlight possible intervention targets for both patient cure and community infection control. While antibiotic therapy offers a practical means of treatment and prevention, the most favorable results are achieved in combination with other methods. This review provides an overview of S. aureus biofilm development, outlines the current range of anti-biofilm agents that are used against each stage and summarizes their relative merits.

Effect of rhamnolipids on the fungal elimination of toluene vapor in a biotrickling filter under stressed operational conditions

The application of rhamnolipids in a fungal-cultured biotrickling filter (BTF) has a significant impact on toluene removal. Two BTFs were used; BTF-A, a control bed, and BTF-B fed with rhamnolipids. The effect of empty bed residence times (EBRTs) on toluene bioavailability was investigated. Removal of toluene was carried out at EBRTs of 30 and 60 s and inlet loading rates (LRs) of 23-184 g m^-3 h^-1. At 30 s EBRT, when inlet LR was increased from 23 to 184 g m^-3 h^-1, the removal efficiency (RE) decreased from 93% to 50% for the control bed, and from 94% to 87% for BTF-B. Increasing the EBRT simultaneously with inlet LRs, confirms that BTF-A was diffusion-limited by registering a RE of 62% for toluene inlet LR of 184 g m^-3 h^-1, whereas BTF-B, achieved RE > 96%, confirming a significant improvement in toluene biodegradability. Overall, the best performance was observed at 60 s EBRT and inlet LR of 184 g m^-3 h^-1, providing a maximum elimination capacity (EC) of 176.8 g m^-3 h^-1 under steady-state conditions. While a maximum EC of 114 g m^-3 h^-1 was observed under the same conditions in the absence of rhamnolipids (BTF-A). Measurements of critical micelle concentration showed that 150 mg L^-1 of rhamnolipids demonstrated the lowest aqueous surface tension and maximum formation of micelles, while 175 mg L^-1 was the optimum dose for fungal growth. Production rate of carbon dioxide, and dissolved oxygen contents highlighted the positive influence of rhamnolipids on adhesive forces, improved toluene mineralization, and promotion of microbial motility over mobility.

Recent Strategies to Combat Biofilms Using Antimicrobial Agents and Therapeutic Approaches

Biofilms are intricate bacterial assemblages that attach to diverse surfaces using an extracellular polymeric substance that protects them from the host immune system and conventional antibiotics. Biofilms cause chronic infections that result in millions of deaths around the world every year. Since the antibiotic tolerance mechanism in biofilm is different than that of the planktonic cells due to its multicellular structure, the currently available antibiotics are inadequate to treat biofilm-associated infections which have led to an immense need to find newer treatment options. Over the years, various novel antibiofilm compounds able to fight biofilms have been discovered. In this review, we have focused on the recent and intensively researched therapeutic techniques and antibiofilm agents used for biofilm treatment and grouped them according to their type and mode of action. We also discuss some therapeutic approaches that have the potential for future advancement.

Phyllosphere-associated microbiota in built environment: Do they have the potential to antagonize human pathogens?

INTRODUCTION

The plant microbiota is known to protect its host against invasion by plant pathogens. Recent studies have indicated that the microbiota of indoor plants is transmitted to the local built environment where it might fulfill yet unexplored functions. A better understanding of the interplay of such microbial communities with human pathogens might provide novel cues related to natural inhibition of them.

OBJECTIVE

We studied the plant microbiota of two model indoor plants, Musa acuminata and Chlorophytum comosum, and their effect on human pathogens. The main objective was to identify mechanisms by which the microbiota of indoor plants inhibits human-pathogenic bacteria.

METHODS

Microbial communities and functioning were investigated using a comprehensive set of experiments and methods combining amplicon and shotgun metagenomic analyses with results from interaction assays.

RESULTS

A diverse microbial community was found to be present on Musa and Chlorophytum grown in different indoor environments; the datasets comprised 1066 bacterial, 1261 fungal, and 358 archaeal ASVs. Bacterial communities were specific for each plant species, whereas fungal and archaeal communities were primarily shaped by the built environment. Sphingomonas and Bacillus were found to be prevalent components of a ubiquitous core microbiome in the two model plants; they are well-known for antagonistic activity towards plant pathogens. Interaction assays indicated that they can also antagonize opportunistic human pathogens. Moreover, the native plant microbiomes harbored a broad spectrum of biosynthetic gene clusters, and in parallel, a variety of antimicrobial resistance genes. By conducting comparative metagenomic analyses between plants and abiotic surfaces, we found that the phyllosphere microbiota harbors features that are clearly distinguishable from the surrounding abiotic surfaces.

CONCLUSIONS

Naturally occurring phyllosphere bacteria can potentially act as a protective shield against opportunistic human pathogens. This knowledge and the underlying mechanisms can provide an important basis to establish a healthy microbiome in built environments.

The Biosynthesis and Metabolism of the N-Acylated Aromatic Amino Acids: N-Acylphenylalanine, N-Acyltyrosine, N-Acyltryptophan, and N-Acylhistidine

The fatty acid amides are a family of lipids composed of two chemical moieties, a fatty acid and a biogenic amine linked together in an amide bond. This lipid family is structurally related to the endocannabinoid anandamide (N-arachidonoylethanolamine) and, thus, is frequently referred to as a family of endocannabinoid-related lipids. The fatty acid amide family is divided into different classes based on the conjugate amine; anandamide being a member of the N-acylethanolamine class (NAE). Another class within the fatty acid amide family is the N-acyl amino acids (NA-AAs). The focus of this review is a sub-class of the NA-AAs, the N-acyl aromatic amino acids (NA-ArAAs). The NA-ArAAs are not broadly recognized, even by those interested in the endocannabinoids and endocannabinoid-related lipids. Herein, the NA-ArAAs that have been identified from a biological source will be highlighted and pathways for their biosynthesis, degradation, enzymatic modification, and transport will be presented. Also, information about the cellular functions of the NA-ArAAs will be placed in context with the data regarding the identification and metabolism of these N-acylated amino acids. A review of the current state-of-knowledge about the NA-ArAAs is to stimulate future research about this underappreciated sub-class of the fatty acid amide family.

Characterization and Cytotoxicity of Pseudomonas Mediated Rhamnolipids Against Breast Cancer MDA-MB-231 Cell Line

A biosurfactant producing bacterium was identified as Pseudomonas aeruginosa DNM50 based on molecular characterization (NCBI accession no. MK351591). Structural characterization using MALDI-TOF revealed the presence of 12 different congeners of rhamnolipid such as Rha-C8-C8:1, Rha-C10-C8:1, Rha-C10-C10, Rha-C10-C12:1, Rha-C16:1, Rha-C16, Rha-C17:1, Rha-Rha-C10:1-C10:1, Rha-Rha-C10-C12, Rha-Rha-C10-C8, Rha-Rha-C10-C8:1, and Rha-Rha-C8-C8. The radical scavenging activity of rhamnolipid (DNM50RL) was determined by 2, 3-diphenyl-1-picrylhydrazyl (DPPH) assay which showed an IC₅₀ value of 101.8 μg/ ml. The cytotoxic activity was investigated against MDA-MB-231 breast cancer cell line by MTT (4,5-dimethylthiazol-2-yl-2,5-diphenyl tetrazolium bromide) assay which showed a very low IC50 of 0.05 μg/ ml at 72 h of treatment. Further, its activity was confirmed by resazurin and trypan blue assay with IC₅₀ values of 0.01 μg/ml and 0.64 μg/ ml at 72 h of treatment, respectively. Thus, the DNM50RL would play a vital role in the treatment of breast cancer targeting inhibition of p38MAPK.

Biofilm formation by Non-O157 Shiga toxin-producing Escherichia coli in monocultures and co-cultures with meat processing surface bacteria

This study investigated the impact of meat processing surface bacteria (MPB) on biofilm formation by non-O157 Shiga toxin-producing Escherichia coli (STEC), and potential links between biofilm formation by STEC and biofilm-related genes in their genomes. Biofilm development by 50 MPB and 6 STEC strains in mono- and co-cultures was assessed by the crystal violet staining method, and their expression of curli and cellulose was determined using the Congo red agar method. Genes (n = 141) associated with biofilm formation in the STEC strains were profiled. Biofilm formation in general correlated with cellulose and curli expression in both mono- and co-cultures. Most MPB strains had antagonistic effects on the biofilm formation of the STEC strains. Of the genes investigated, 81% were common among the STEC strains and there seems to be a gene-redundancy in biofilm formation. The inability of the O26 strain to form biofilms could be due to mutations in the rpoS gene. Truncation in the mlrA gene in the O145 strain seems not affecting its biofilm formation alone or with MPB. The O45 strain, despite having the greatest number of biofilm-related genes, did not form measurable biofilms. Overall, biofilm formation of STEC was affected by curli-cellulose expression and companion strains.

Rhamnolipids as a Tool for Eradication of Trichosporon cutaneum Biofilm

Microbial biofilms formed by pathogenic and antibiotic-resistant microorganisms represent a serious threat for public health in medicine and many industrial branches. Biofilms are involved in many persistent and chronic infections, the biofouling of water and food contamination. Therefore, current research is involved in the development of new treatment strategies. Biofilm is a complex system, and thus all aspects of the measurement and monitoring of its growth and eradication in various conditions, including static and dynamic flow, are issues of great importance. The antibiofilm character of rhamnolipid mixtures produced by four Pseudomonas aeruginosa strains was studied under different conditions. For this purpose, the biofilm of opportunistic pathogen Trichosporon cutaneum was used and treated under static conditions (microscope glass coverslip in a Petri dish) and under dynamic conditions (a single-channel flow cell). The results show that the biological activity of rhamnolipids depends both on their properties and on the conditions of the biofilm formation. Therefore, this aspect must be taken into account when planning the experimental or application design.

Functional and Structural Characterization of Pediococcus pentosaceus-Derived Biosurfactant and Its Biomedical Potential against Bacterial Adhesion, Quorum Sensing, and Biofilm Formation

Biosurfactants are surface-active molecules of microbial origin and alternatives to synthetic surfactants with various applications. Due to their environmental-friendliness, biocompatibility, biodegradability, effectiveness to work under various environmental conditions, and non-toxic nature, they have been recently recognized as potential agents with therapeutic and commercial importance. The biosurfactant produced by various probiotic lactic acid bacteria (LAB) has enormous applications in different fields. Thus, in vitro assessment of biofilm development prevention or disruption by natural biosurfactants derived from probiotic LAB is a plausible approach that can lead to the discovery of novel antimicrobials. Primarily, this study aims to isolate, screen, and characterize the functional and biomedical potential of biosurfactant synthesized by probiotic LAB Pediococcus pentosaceus (P. pentosaceus). Characterization consists of the assessment of critical micelle concentration (CMC), reduction in surface tension, and emulsification index (% EI24). Evaluation of antibacterial, antibiofilm, anti-QS, and anti-adhesive activities of cell-bound biosurfactants were carried out against different human pathogenic bacteria (B. subtilis, P. aeruginosa, S. aureus, and E. coli). Moreover, bacterial cell damage, viability of cells within the biofilm, and exopolysaccharide (EPS) production were also evaluated. As a result, P. pentosaceus was found to produce 4.75 ± 0.17 g/L biosurfactant, which displayed a CMC of 2.4 ± 0.68 g/L and reduced the surface tension from 71.11 ± 1.12 mN/m to 38.18 ± 0.58 mN/m. P. pentosaceus cells bound to the crude biosurfactant were found to be effective against all tested bacterial pathogens. It exhibited an anti-adhesion ability and impeded the architecture of the biofilm matrix by affecting the viability and integrity of bacterial cells within biofilms and reducing the total EPS content. Furthermore, the crude biosurfactant derived from P. pentosaceus was structurally characterized as a lipoprotein by GC-MS analysis, which confirms the presence of lipids and proteins. Thus, our findings represent the potent anti-adhesion and antibiofilm potential of P. pentosaceus crude biosurfactant for the first time, which may be explored further as an alternative to antibiotics or chemically synthesized toxic antibiofilm agents.

Biosurfactants: Potential Agents for Controlling Cellular Communication, Motility, and Antagonism

Biosurfactants are surface-active molecules produced by microorganisms, either on the cell surface or secreted extracellularly. They form a thin film on the surface of microorganisms and help in their detachment or attachment to other cell surfaces. They are involved in regulating the motility of bacteria and quorum sensing. Here, we describe the various types of biosurfactants produced by microorganisms and their role in controlling motility, antagonism, virulence, and cellular communication.

Nickel stress-tolerance in plant-bacterial associations

Nickel (Ni) is an essential element for plant growth and is a constituent of several metalloenzymes, such as urease, Ni-Fe hydrogenase, Ni-superoxide dismutase. However, in high concentrations, Ni is toxic and hazardous to plants, humans and animals. High levels of Ni inhibit plant germination, reduce chlorophyll content, and cause osmotic imbalance and oxidative stress. Sustainable plant-bacterial native associations are formed under Ni-stress, such as Ni hyperaccumulator plants and rhizobacteria showed tolerance to high levels of Ni. Both partners (plants and bacteria) are capable to reduce the Ni toxicity and developed different mechanisms and strategies which they manifest in plant-bacterial associations. In addition to physical barriers, such as plants cell walls, thick cuticles and trichomes, which reduce the elevated levels of Ni entrance, plants are mitigating the Ni toxicity using their own antioxidant defense mechanisms including enzymes and other antioxidants. Bacteria in its turn effectively protect plants from Ni stress and can be used in phytoremediation. PGPR (plant growth promotion rhizobacteria) possess various mechanisms of biological protection of plants at both whole population and single cell levels. In this review, we highlighted the current understanding of the bacterial induced protective mechanisms in plant-bacterial associations under Ni stress.

Development of a novel micro-bead force spectroscopy approach to measure the ability of a thermo-active polymer to remove bacteria from a corneal model

Microbial keratitis occurs from the infection of the cornea by fungi and or bacteria. It remains one of the most common global causes of irreversible blindness accounting for 3.5% (36 million) of blind people as of 2015. This paper looks at the use of a bacteria binding polymer designed to bind Staphylococcus aureus and remove it from the corneal surface. Mechanical unbinding measurements were used to probe the interactions of a thermo-active bacteria-binding polymer, highly-branched poly(N-isopropyl acrylamide), functionalised with modified vancomycin end groups (HB-PNIPAM-Van) to bacteria placed on rabbit corneal surfaces studied ex-vivo. This was conducted during sequential temperature phase transitions of HB-PNIPAM-Van-S. aureus below, above and below the lower critical solution temperature (LCST) in 3 stages, in-vitro, using a novel micro-bead force spectroscopy (MBFS) approach via atomic force microscopy (AFM). The effect of temperature on the functionality of HB-PNIPAM-Van-S. aureus showed that the polymer-bacteria complex reduced the work done in removing bacterial aggregates at T > LCST (p < 0.05), exhibiting reversibility at T < LCST (p < 0.05). At T < LCST, the breaking force, number of unbinding events, percentage fitted segments in the short and long range, and the percentage of unbinding events occurring in the long range (> 2.5 µm) increased (p < 0.05). Furthermore, the LCST phase transition temperature showed 100 × more unbinding events in the long-range z-length (> 2.5 µm) compared to S. aureus aggregates only. Here, we present the first study using AFM to assess the reversible mechanical impact of a thermo-active polymer-binding bacteria on a natural corneal surface.

Surfactants of microbial origin as antibiofilm agents

The microbial world provides new energy sources and many various 'green' chemicals. One type of chemicals produced by microorganisms is the biosurfactant group. Biosurfactants are universal molecules, exhibiting surface properties often accompanied by desired biological activity. Biosurfactants are considered to be environmentally 'friendly' due to their low toxicity and biodegradable nature. These compounds have unique features and therefore they can find potential applications in many different industries, ranging from biotechnology to environmental remediation technologies. Antibacterial and antifungal activities make them relevant for applications as inhibitory agents against microbial biofilm. This review covers the current knowledge and the recent advances in the field of biosurfactants as antibiofilm agents.

A novel anti-infective molecule nesfactin identified from sponge associated bacteria Nesterenkonia sp. MSA31 against multidrug resistant Pseudomonas aeruginosa

Overuse of antibiotics coupled with biofilm-forming ability has led to the emergence of multi-drug P. aeruginosa strains worldwide. Quorum sensing is a bacterial cell-cell communication system that regulates the expression of genes, including virulence factors, through production of acyl-homoserine lactones (AHLs) in Pseudomonas aeruginosa. The phenotypic expression of virulence factors in P. aeruginosa is mediated by quorum sensing systems (las and rhl). In this study an anti-infective molecule produced by a marine actinomycetes Nesterenkonia sp. MSA31 was elucidated as lipopeptide by NMR and LC-MS/MS analysis. The new lipopeptide molecule was named Nesfactin. This molecule effectively inhibited virulence phenotypes including production of hemolysin, protease, lipase, phospholipase, esterase, elastase, rhamnolipid, alginate, and pyocyanin, as well as motility and biofilm formation in P. aeruginosa. The high-performance thin layer chromatography (HPTLC) analysis revealed that the lipopeptide (50 μg/mL) inhibited production of the AHLs produced by the las and rhl quorum sensing systems (3-oxo-C12-HSL and C4-HSL, respectively). Docking analysis showed the binding affinity of the ligand towards the quorum sensing receptor molecules. The confocal laser scanning microscopy images showed the anti-biofilm effect of lipopeptide against P. aeruginosa. Nesfactin based hydrogel showed a significant antibiofilm effect on the catheter. This study suggests that the lipopeptide may be an effective anti-virulence treatment for Pseudomonas aeruginosa infections.

Recent Advances in Biomedical, Therapeutic and Pharmaceutical Applications of Microbial Surfactants

The spread of antimicrobial-resistant pathogens typically existing in biofilm formation and the recent COVID-19 pandemic, although unrelated phenomena, have demonstrated the urgent need for methods to combat such increasing threats. New avenues of research for natural molecules with desirable properties to alleviate this situation have, therefore, been expanding. Biosurfactants comprise a group of unique and varied amphiphilic molecules of microbial origin capable of interacting with lipidic membranes/components of microorganisms and altering their physicochemical properties. These features have encouraged closer investigations of these microbial metabolites as new pharmaceutics with potential applications in clinical, hygiene and therapeutic fields. Mounting evidence has indicated that biosurfactants have antimicrobial, antibiofilm, antiviral, immunomodulatory and antiproliferative activities that are exploitable in new anticancer treatments and wound healing applications. Some biosurfactants have already been approved for use in clinical, food and environmental fields, while others are currently under investigation and development as antimicrobials or adjuvants to antibiotics for microbial suppression and biofilm eradication strategies. Moreover, due to the COVID-19 pandemic, biosurfactants are now being explored as an alternative to current products or procedures for effective cleaning and handwash formulations, antiviral plastic and fabric surface coating agents for shields and masks. In addition, biosurfactants have shown promise as drug delivery systems and in the medicinal relief of symptoms associated with SARS-CoV-2 acute respiratory distress syndrome.

Multiple biosurfactant production by Aureobasidium pullulans strain YTP6-14 in aqueous and heavy oil layers

Aureobasidium pullulans YTP6-14 was demonstrated to be an excellent multiple biosurfactant producer utilizing cheap carbon sources available in Thailand, including glycerol and cassava flour hydrolysate. A. pullulans YTP6-14 maximally produced 1.81 g/l biosurfactant in an aqueous layer (BS-AQ) in a medium containing glycerol, and 7.37 or 6.37 g/l biosurfactant in a heavy oil layer (BS-HO) in cassava flour hydrolysate or a glucose containing medium, respectively. Each BS-AQ and BS-HO had critical micelle concentration values of 41.32 mg/l and 13.51 mg/l, and both biosurfactants formed a stable food oil emulsion and reduced the amount of biofilms formed by Streptococcus sobrinus and Streptococcus mutans. BS-AQ and BS-HO were mainly composed of liamocins or exophilins and massoia lactone, respectively.

Contributions of Glycolipid Biosurfactants and Glycolipid-Modified Materials to Antimicrobial Strategy: A Review

Glycolipid biosurfactants are natural amphiphiles and have gained particular interest recently in their biodegradability, diversity, and bioactivity. Microbial infection has caused severe morbidity and mortality and threatened public health security worldwide. Glycolipids have played an important role in combating many diseases as therapeutic agents depending on the self-assembly property, the anticancer and anti-inflammatory properties, and the antimicrobial properties, including antibacterial, antifungal, and antiviral effects. Besides, their role has been highlighted as scavengers in impeding the biofilm formation and rupturing mature biofilm, indicating their utility as suitable anti-adhesive coating agents for medical insertional materials leading to a reduction in vast hospital infections. Notably, glycolipids have been widely applied to the synthesis of novel antimicrobial materials due to their excellent amphipathicity, such as nanoparticles and liposomes. Accordingly, this review will provide various antimicrobial applications of glycolipids as functional ingredients in medical therapy.

Effect of surfactin on removal of semi-volatile organic compound: Emphasis on enhanced biofiltration performance

The performance of a lab-scale biotrickling filter (BTF) inoculated with a mixed fungal consortium was investigated for the simultaneous abatement of 2-ethylhexanol; a hydrophobic semi-volatile organic compound (SVOC), and propylene glycol monomethyl ether (PGME). The BTF performance was investigated in the presence of lipopeptide-type biosurfactant, surfactin. The effect of surfactin on the removal efficiency and elimination capacity was examined at stretched inlet loading rates (LR): 1.04 to 15.7 and 3.2-48 g m^-3 h^-1 of PGME and 2-ethylhexanol, respectively. Seeding the BTF with 50 mg L^-1 of surfactin maintained high and consistent removal efficiencies of PGME and 2-ethylhexanol up to LRs of 15.7 and 32 g m^-3 h^-1, with removal efficiencies of 98.5 and 99%, respectively. Once the LR of 2-ethylhexanol increased to 48 g m^-3 h^-1, a substrate inhibition was observed, accompanied by a sudden decrease in removal efficiency from 99.2 to 62.3%. At the same LR, the BTF performance was improved by reseeding 100 mg L^-1 of surfactin, hence, reinstated the removal efficiency of 2-ethylhexanol to 92.7% and achieving a maximum elimination capacity of 44.5 g m^-3 h^-1. This enhanced SVOC uptake rate was further confirmed by a considerable increase in reaction rate constant from 0.005 to 0.017 s^-1. A batch study was also conducted at the end of the experimental run to better understand the correlation between surfactin concentrations and the time-dependent partition coefficient of 2-ethylhexanol. Biofilm microbial community structure revealed relative abundancy of 72 and 28% of Trichoderma asperellum and Fusarium solani, respectively. The findings of this study show for the first time that the removal of a semi-VOC such as 2-ethylhexanol is feasible in the presence of surfactin and hence improving the bioavailability of hydrophobic semi-VOC.

Inhibitory Effects of Lipopeptides and Glycolipids on C. albicans-Staphylococcus spp. Dual-Species Biofilms

Microbial biofilms strongly resist host immune responses and antimicrobial treatments and are frequently responsible for chronic infections in peri-implant tissues. Biosurfactants (BSs) have recently gained prominence as a new generation of anti-adhesive and antimicrobial agents with great biocompatibility and were recently suggested for coating implantable materials in order to improve their anti-biofilm properties. In this study, the anti-biofilm activity of lipopeptide AC7BS, rhamnolipid R89BS, and sophorolipid SL18 was evaluated against clinically relevant fungal/bacterial dual-species biofilms (Candida albicans, Staphylococcus aureus, Staphylococcus epidermidis) through quantitative and qualitative in vitro tests. C. albicans-S. aureus and C. albicans-S. epidermidis cultures were able to produce a dense biofilm on the surface of the polystyrene plates and on medical-grade silicone discs. All tested BSs demonstrated an effective inhibitory activity against dual-species biofilms formation in terms of total biomass, cell metabolic activity, microstructural architecture, and cell viability, up to 72 h on both these surfaces. In co-incubation conditions, in which BSs were tested in soluble form, rhamnolipid R89BS (0.05 mg/ml) was the most effective among the tested BSs against the formation of both dual-species biofilms, reducing on average 94 and 95% of biofilm biomass and metabolic activity at 72 h of incubation, respectively. Similarly, rhamnolipid R89BS silicone surface coating proved to be the most effective in inhibiting the formation of both dual-species biofilms, with average reductions of 93 and 90%, respectively. Scanning electron microscopy observations showed areas of treated surfaces that were free of microbial cells or in which thinner and less structured biofilms were present, compared to controls. The obtained results endorse the idea that coating of implant surfaces with BSs may be a promising strategy for the prevention of C. albicans-Staphylococcus spp. colonization on medical devices, and can potentially contribute to the reduction of the high economic efforts undertaken by healthcare systems for the treatment of these complex fungal-bacterial infections.

Rhamnolipid the Glycolipid Biosurfactant: Emerging trends and promising strategies in the field of biotechnology and biomedicine

Rhamnolipids (RLs) are surface-active compounds and belong to the class of glycolipid biosurfactants, mainly produced from Pseudomonas aeruginosa. Due to their non-toxicity, high biodegradability, low surface tension and minimum inhibitory concentration values, they have gained attention in various sectors like food, healthcare, pharmaceutical and petrochemicals. The ecofriendly biological properties of rhamnolipids make them potent materials to be used in therapeutic applications. RLs are also known to induce apoptosis and thus, able to inhibit proliferation of cancer cells. RLs can also act as immunomodulators to regulate the humoral and cellular immune systems. Regarding their antimicrobial property, they lower the surface hydrophobicity, destruct the cytoplasmic membrane and lower the critical micelle concentration to kill the bacterial cells either alone or in combination with nisin possibly due to their role in modulating outer membrane protein. RLs are also involved in the synthesis of nanoparticles for in vivo drug delivery. In relation to economic benefits, the post-harvest decay of food can be decreased by RLs because they prevent the mycelium growth, spore germination of fungi and inhibit the emergence of biofilm formation on food. The present review focuses on the potential uses of RLs in cosmetic, pharmaceutical, food and health-care industries as the potent therapeutic agents.

Investigation of halotolerant marine Staphylococcus sp. CO100, as a promising hydrocarbon-degrading and biosurfactant-producing bacterium, under saline conditions

A halotolerant strain CO100 of Staphylococcus sp. was isolated from contaminated sediments taken from the fishing harbour of Sfax, Tunisia, as an efficient hydrocarbonoclastic candidate. Strain CO100 exhibited a high capacity to break down almost 72% of the aliphatic hydrocarbons contained in crude oil (1%, v/v), used as the sole carbon and energy source, after 20 days of culture, at 100 g/l NaCl, 37 °C and 180 rpm. The isolate CO100 displayed also its ability to grow on phenanthrene, fluoranthene and pyrene (100 mg/l), at 100 g/l NaCl. Moreover, the isolate CO100 showed a notable aptitude to synthesize an efficient tensioactive agent namely BS-CO100, on low-value substrates including residual frying oil and expired milk powder, thus reducing the high cost of biosurfactant production. The ESI/MS analysis designated that BS-CO100 belonged to lipopeptide class, in particular lichenysin and iturine members. Critical micelle concentrations of BS-CO100 were varying between 65 and 750 mg/l, depending on of the purity of the biosurfactant and the used carbon sources. BS-CO100 showed a high steadiness against a wide spectrum of pH (4.3-12), temperature (4-121 °C) and salinity (0-300 g/l NaCl), supporting its powerful tensioactive properties under various environmental conditions. Likewise, BS-CO100 exhibited no cytotoxic effect toward human HEK293 cells, at concentrations within 125 and 1000 μg/ml. Furthermore, the biosurfactant BS-CO100 exhibited remarkable anti-adhesive and anti-biofilm activities, being able to avoid and disrupt the biofilm formation by certain pathogenic microorganisms. In addition, BS-CO100 was found to have more potential to remove hydrocarbons from contaminated soils, compared to some chemical surfactants. In light of these promising findings, strain CO100, as well as its biosurfactant, could be successfully used in different biotechnological applications including the bioremediation of oil-polluted areas, even under saline conditions.

Biosurfactants’ Potential Role in Combating COVID-19 and Similar Future Microbial Threats

During 2020, the world has experienced extreme vulnerability in the face of a disease outbreak. The coronavirus disease 2019 (COVID-19) pandemic discovered in China and rapidly spread across the globe, infecting millions, causing hundreds of thousands of deaths, and severe downturns in the economies of countries worldwide. Biosurfactants can play a significant role in the prevention, control and treatment of diseases caused by these pathogenic agents through various therapeutic, pharmaceutical, environmental and hygiene approaches. Biosurfactants have the potential to inhibit microbial species with virulent intrinsic characteristics capable of developing diseases with high morbidity and mortality, as well as interrupting their spread through environmental and hygiene interventions. This is possible due to their antimicrobial activity, ability to interact with cells forming micelles and to interact with the immune system, and compatibility with relevant processes such as nanoparticle synthesis. They, therefore, can be applied in developing innovative and more effective pharmaceutical, therapeutics, sustainable and friendly environmental management approaches, less toxic formulations, and more efficient cleaning agents. These approaches can be easily integrated into relevant product development pipelines and implemented as measures for combating and managing pandemics. This review examines the potential approaches of biosurfactants as useful molecules in fighting microbial pathogens both known and previously unknown, such as COVID-19.

Preparation of silver-decorated Soluplus® nanoparticles and antibacterial activity towards S. epidermidis biofilms as characterized by STEM-CL spectroscopy

Biofilm infections present a serious problem because antibacterial drugs are not effective against mature biofilms or biofilms formed by drug-resistant bacteria. To address this issue, we developed a drug delivery system based on metal-decorated polymeric particles. Polyvinyl caprolactam-polyvinyl acetate-polyethylene glycol graft copolymer (Soluplus®) is an amphiphilic polymer used in biomedical formulations, while silver nanoparticles are widely acknowledged to have high antibacterial activity. We prepared silver-decorated Soluplus® micelle nanoparticles with high antibacterial activity using the emulsion solvent diffusion method. Decoration of Soluplus® micelles with silver nanoparticles was found to increase their antibacterial activity. Scanning transmission electron microscopy-cathodoluminescence (STEM-CL) spectroscopy allows imaging of the spatial distribution of labeled targets and the chemical identification of materials. However, STEM-CL spectroscopy of fragile polymer materials is challenging. We optimized the STEM-CL spectroscopy technique to determine the distribution of silver nanoparticles in Soluplus® micelles. Additionally, the surface plasmon properties of the silver nanoparticles were successfully characterized without deactivation. The developed silver-decorated Soluplus® nanoparticles were effective against biofilm infections and have the potential to be applied for other biofilm-related diseases. Additionally, the optimized STEM-CL spectroscopy technique is expected to contribute to the analysis and imaging of fragile polymer materials, as well as other soft materials such as cells and tissues.

The use of low-cost brewery waste product for the production of surfactin as a natural microbial biocide

•

For the first time Bacillus subtilis was able to grow in a culture medium containing Brewery waste (Trub) and produced surfactin.

•

Surfactin showed bactericidal effect against Pseudomonas aeruginosa.

•

P. aeruginosa biofilm was inhibited (79.8%) when co-incubated with surfactin.

•

Surfactin showed anti-adhesive activity on polystyrene surfaces.

•

P. aeruginosa biofilm was disrupted (44.9%) when treated with surfactin (700 μg/mL).

Surfactin has potential as next generation antibiofilm agent to combat antimicrobial resistance against emerging pathogens. However, the widespread industrial applications of surfactin is hampered by its high production cost. In this work, surfactin was produced from Bacillus subtilis using a low-cost brewery waste as a carbon source. The strain produced 210.11 mg L−1 after 28 h. The antimicrobial activity was observed against all tested strains, achieving complete inhibition for Pseudomonas aeruginosa, at 500 μg mL−1. A growth log reduction of 3.91 was achieved for P. aeruginosa while, Staphylococcus aureus and Staphylococcus epidermidis showed between 1 and 2 log reductions. In the anti-biofilm assays against P. aeruginosa, the co-incubation, anti-adhesive and disruption showed inhibition, where the greatest inhibition was observed in the co-incubation assay (79.80%). This study provides evidence that surfactin produced from a low-cost substrate can be a promising biocide due to its antimicrobial and anti-biofilm abilities against pathogens.

Microbial Biosurfactants in Cosmetic and Personal Skincare Pharmaceutical Formulations

Cosmetic and personal care products are globally used and often applied directly on the human skin. According to a recent survey in Europe, the market value of cosmetic and personal care products in Western Europe reached about 84 billion euros in 2018 and are predicted to increase by approximately 6% by the end of 2020. With these significant sums of money spent annually on cosmetic and personal care products, along with chemical surfactants being the main ingredient in a number of their formulations, of which many have been reported to have the potential to cause detrimental effects such as allergic reactions and skin irritations to the human skin; hence, the need for the replacement of chemical surfactants with other compounds that would have less or no negative effects on skin health. Biosurfactants (surfactants of biological origin) have exhibited great potential such as lower toxicity, skin compatibility, protection and surface moisturizing effects which are key components for an effective skincare routine. This review discusses the antimicrobial, skin surface moisturizing and low toxicity properties of glycolipid and lipopeptide biosurfactants which could make them suitable substitutes for chemical surfactants in current cosmetic and personal skincare pharmaceutical formulations. Finally, we discuss some challenges and possible solutions for biosurfactant applications.