Microbial biofilms: biosurfactants as antibiofilm agents.

Current microbial inhibition strategies based on planktonic bacterial physiology have been known to have limited efficacy on the growth of biofilm communities. This problem can be exacerbated by the emergence of increasingly resistant clinical strains. All aspects of biofilm measurement, monitoring, dispersal, control, and inhibition are becoming issues of increasing importance. Biosurfactants have merited renewed interest in both clinical and hygienic sectors due to their potential to disperse microbial biofilms in addition to many other advantages. The dispersal properties of biosurfactants have been shown to rival those of conventional inhibitory agents against bacterial and yeast biofilms. This makes them suitable candidates for use in new generations of microbial dispersal agents and for use as adjuvants for existing microbial suppression or eradication strategies. In this review, we explore aspects of biofilm characteristics and examine the contribution of biologically derived surface-active agents (biosurfactants) to the disruption or inhibition of microbial biofilms

Biosurfactant Production in Aerobic and Anaerobic Conditions by Different Species of the Genus Pseudomonas

In a time where surface active agents are capable of reducing the energy of the bonds between water molecules by interacting with them to reduce surface tension, it would be unwise not to be able to generate these in masses. Different Pseudomonas species were grown in MSP (minimal sulphate phosphate) media containing salts, glycerol and glucose. P. aeruginosa grown aerobically in the presence of glycerol as carbon source showed the highest emulsion percentage (81.48%), most significant decrease in surface tension (20 mN/m) and rhamnose production of 2.86 mg/mL. However, in anaerobic conditions there was no emulsion, rhamnolipid production or decrease in surface tension. The rhamnolipids were molecularly characterized using ESI-MS (electrospray ionization-mass spectrometry), P. aeruginosa CVCM 411 is able to produce mono-rhamnolipids and di-rhamnolipids, being rhamnolipid RhC10C12:1 the predominant monomer. The specific growth rate for isolates of P. aeruginosa and P. fluorescens in MSP are 0.6732 h-1 and 0.2181 h-1, respectively. In conclusion, the formation of rhamnolipids by P. aeruginosa is linked to its growth (depending on μ), and its ability to generate about 35% of the μmax, in the presence of glucose (carbon source) and glycerol (applied as pulses)

Pseudomonas aeruginosa biofilm disruption using microbial surfactants.

AIMS: To establish the ability of the rhamnolipids biosurfactants from Pseudomonas aeruginosa, in the presence and absence of caprylic acid and ascorbic acid, to disrupt bacterial biofilms, compared with the anionic alkyl sulphate surfactant Sodium dodecyl sulphate (SDS). METHODS AND RESULTS: Pseudomonas aeruginosa ATCC 15442 biofilms were disrupted by rhamnolipids at concentrations between 0·5 and 0·4 g l(-1) and with SDS at 0·8 g l(-1) . The combination of rhamnolipids 0·4 g l(-1) and caprylic acid at 0·1 g l(-1) showed a remarkable effect on biofilm disruption and cell killing. After 30 min of treatment most of the biofilm was disrupted and cell viability was significantly reduced. Neither caprylic acid nor ascorbic acid has any effect on biofilm disruption at 0·1 g l(-1) . SDS is an effective antimicrobial agent; however, in the presence of caprylic acid its effect was neutralized. CONCLUSIONS: The results show that rhamnolipids at low concentration in the presence of caprylic acid are promising molecules for inhibition/disruption of biofilms formed by Ps. aeruginosa ATCC 15442. SIGNIFICANCE AND IMPACT OF THE STUDY: The disruption of biofilms has major significance in many industrial and domestic cleaning applications and in medical situations

A GRANULAR FORMULATION OF Nomuraea rileyi Farlow (Samson) FOR THE CONTROL OF Spodoptera frugiperda (LEPIDOPTERA: NOCTUIDAE)

A granular formulation of the entomopathogenic fungus Nomuraea rileyi (Farlow) Samson was evaluated against Spodoptera frugiperda (Lepidoptera: Noctuidae). The formulation consisted of 1mm particles of defatted corn germ (DCG) containing 107 conidia/g. This preparation protected the conidia against UV radiation and killed 80% of S. frugiperda larvae in laboratory bioassays. It was shown that the fungus used DCG as a substrate for growth and sporulation, creating foci for further infection. This strategy has great potential for the formulation of fungal biocontrol agents, especially those with a high growth rate

The effect of sophorolipids against microbial biofilms on medical-grade silicone

Recent medical strategies rely on the search for effective antimicrobials as surface coatings to prevent and treat infections in humans and animals. Biosurfactants have recently been shown to have properties as antiadhesive and antibiofilm agents. Sophorolipids in particular are biosurfactant molecules known to act as therapeutic agents. This study aimed to evaluate antimicrobial properties of sophorolipids in medical-grade silicone discs using strains of clinical relevance. Sophorolipids were produced under fed batch conditions, ESI-MS analyses were carried out to confirm the congeners present in each formulation. Three different products were obtained SLA (acidic congeners), SL18 (lactonic congeners) and SLV (mixture of acidic and lactonic congeners) and were tested against Staphylococcus aureus ATCC 6538, Pseudomonas aeruginosa ATCC 10145 and Candida albicans IHEM 2894. All three congener mixtures showed a biofilms disruption effect (> 0.1% w/v) of 70%, 75% and 80% for S. aureus, P. aeruginosa and C. albicans, respectively. On pre-coated silicone discs, biofilm formation of S. aureus was reduced by 75% using SLA 0.8% w/v. After 1.5 h the inhibition of C. albicans attachment was between 45-56% whilst after 24 h incubation the percentage of inhibition for the cell attachment increased to 68-70% when using SLA 0.8% w/v. Finally, in co-incubation experiments SLA 0.05% w/v significantly reduced the ability of S. aureus and C. albicans to form biofilms and to adhere to surfaces by 90-95% at concentrations between 0.025-0.1% w/v. In conclusion sophorolipids significantly reduced the cell attachment of both tested strains which suggests that these molecules could have a potential role as coating agents on medical grade silicone devices for the preventions of Gram positive bacteria and yeast infections

Use of electrical resistance tomography (ERT) for the detection of biofilm disruption mediated by biosurfactants

© 2018 Institution of Chemical Engineers Inline measurement of biofilms could provide a valuable technology for water, food and bioprocessing industries to improve quality control and avoid contamination. This study presents the first use of electrical resistance tomography (ERT) to detect the removal of biofilms in a pipe. It also tests the effectiveness of sophorolipids and rhamnolipids for the disruption of Bacillus subtilis BBK006 biofilms in an industrial setting. Biofilms were grown on the inner side of a section of 1.5″ test pipe for 5 days using nutrient broth as the culture medium. After the medium was removed the test pipe was incorporated into a cleaning test circuit for the biofilm disruption experiment, where water, sophorolipids (0.4 g L−1) or rhamnolipids (0.4 g L−1) solutions were pumped through respectively for 30 min. ERT was used as an indirect evaluation of the film disruption progression. A cleaning parameter was identified based on zonal boundary averages which successfully measured the extent of biofilm removal

Influence of microbial adherence on corrosion of UNS 1008 carbon steel and hybrid nano-structured coatings

Microbiologically induced corrosion (MIC) causes the degradation of coatings and it can be attributed to either direct or indirect microbial metabolic activity. In this study, we report the ability of sulphate reducing microorganisms (SRM) and marine strain bacteria to attach onto UNS1008 carbon steel, and zinc rich epoxy coatings with a content of carbon nanotubes (CNTs) respectively. In aerobic conditions the outer layer presents a micro-crack appearance and many semisphere products, attributed to spore formation. In anaerobic conditions, evidence of iron sulphide surrounded by a mixture of sulphur-containing extracellular polymer substance was observed by SEM images and EDS analysis. The presence of hybrid coatings (Zn rich epoxy with CNT content) affected the level of microbial adherence and the concentration of corrosion products (Fe2O3, Fe(OH)2, FeS); the cell attachment was lower when the steel surface was coated with Zn/CNTs

Influence of microbial adherence on corrosion of UNS 1008 carbon steel and hybrid nano-structured coatings

Microbiologically induced corrosion (MIC) causes the degradation of coatings and it can be attributed to either direct or indirect microbial metabolic activity. In this study, we report the ability of sulphate reducing microorganisms (SRM) and marine strain bacteria to attach onto UNS1008 carbon steel, and zinc rich epoxy coatings with a content of carbon nanotubes (CNTs) respectively. In aerobic conditions the outer layer presents a micro-crack appearance and many semisphere products, attributed to spore formation. In anaerobic conditions, evidence of iron sulphide surrounded by a mixture of sulphur-containing extracellular polymer substance was observed by SEM images and EDS analysis. The presence of hybrid coatings (Zn rich epoxy with CNT content) affected the level of microbial adherence and the concentration of corrosion products (Fe2O3, Fe(OH)2, FeS); the cell attachment was lower when the steel surface was coated with Zn/CNTs

Diffusive Release of Photosensitizing Agents (PS) from Novel PVA-Borate Semi-Solid Drug Carriers Through In Vitro Oral Streptococcus mutans Biofilm

Background: Streptococcus mutans, one of the agent of human dental caries, is particularly effective at forming biofilms on the hard tissues of the human oral cavity; the purpose of this study was to investigate and quantify the diffusional release of photosentising agents (PS): methylene blue (MB), toludine blue (TB), rose bengal (RB) and methyl orange (MO) from Polyvinyl alcohol (PVA)-borate semi-solid gels in the presence of in vitro oral Streptococcus mutans biofilm. Methods: S. mutans biofilm growths were ascertained to ensure proper dental plaque formation and were characterized using confocal microscopy. Release profiles for MB, TB, RB and MO-loaded PVA-borate semi-solids in the absence of biofilms were directly compared to their counterparts in the presence of S. mutans biofilms. In addition, their diffusion coefficients and resistances were determined. Results: The confocal imaging results showed that biofilms grown over a 5-day period had a generally uninterrupted film of colonies occupying the entire surface area of growth surface of a nylon mesh support with approximately 60 µm biofilm size. The overall diffusion resistance of all PVA-borate semi-solids in the presence of S. mutans biofilms was about 1.2 times lower than the diffusion resistance for PVAborate semi-solids in the absence of biofilms. The diffusion resistances for all studied PS, indicate that electrostatic forces and molecular size play an important part in controlled and sustained drug release from PVA-borate semi-solids. Conclusions: PVA-borate semi-solids as novel PSs carriers might offer an innovative delivery system in the treatment against Streptococcus mutans

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 72h on both these surfaces. In co-incubation conditions, in which BSs were tested in free soluble form, rhamnolipid R89BS (0.05 mg/ml) was the most effective among the tested biosurfactants against the formation of both dual-species biofilms, reducing on average 94% and 95% of biofilm biomass and metabolic activity at 72h 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