Sub-lethal concentrations of Perilla frutescens essential oils affect phytopathogenic fungal biofilms.

The lack of deep knowledge of plant pathogenic fungal biofilms is reflected in the few existing environmental-friendly options for controlling fungal plant disease. Indeed, chemical fungicides still dominate the market but present-day concerns about their real efficacy, increasing awareness of the risk they pose to human health and the environment, and the incidence of fungicide resistance have all led to the current trend of near zero-market-tolerance for pesticide residues in fruit and vegetables. Here, essential oils (PK and PK-IK) from the edible leaves of two cultivars of Perilla frutescens are proposed as new, effective, non-toxic, eco-friendly pesticide-free options suitable for a preventive or integrative approach for sustainable crop protection and product preservation. PK and PK-IK were extracted and characterized, and their ability to affect the biofilm formation of the phytopathogenic model fungi Colletotrichum musae, Fusarium dimerum and Fusarium oxysporum was studied at non-lethal doses. Both essential oils at 1000 and 2000 mg l-1 showed excellent anti-biofilm performance: i) reducing conidia adhesion up to 80.3 ±â€¯16.2%; ii) inhibiting conidia germination up to 100.0 ±â€¯0.0%; iii) affecting biofilm structural development, with a reduction in dry weight of up to 100.0 ±â€¯0.0% and extracellular polysaccharides and proteins up to 81.4 ±â€¯8.0% and 51.0 ±â€¯6.1% respectively. In all cases PK-IK showed better activity than PK.

Hindering the formation and promoting the dispersion of medical biofilms: non-lethal effects of seagrass extracts.

BACKGROUND: Biofilms have great significance in healthcare-associated infections owing to their inherent tolerance and resistance to antimicrobial therapies. New approaches to prevent and treat unwanted biofilms are urgently required. To this end, three seagrass species (Enhalus acoroides, Halophila ovalis and Halodule pinifolia) collected in Vietnam and in India were investigated for their effects in mediating non-lethal interactions on sessile bacterial (Escherichia coli) and fungal (Candida albicans) cultures. The present study was focused on anti-biofilm activities of seagrass extracts, without killing cells. METHODS: Methanolic extracts were characterized, and major compounds were identified by MS/MS analysis. The antibiofilm properties of the seagrass extracts were tested at sub-lethal concentrations by using microtiter plate adhesion assay. The performance of the most promising extract was further investigated in elegant bioreactors to reproduce mature biofilms both at the solid/liquid and the solid/air interfaces. Dispersion and bioluminescent assays were carried out to decipher the mode of action of the bioactive extract. RESULTS: It was shown that up to 100 ppm of crude extracts did not adversely affect microbial growth, nor do they act as a carbon and energy source for the selected microorganisms. Seagrass extracts appear to be more effective in deterring microbial adhesion on hydrophobic surfaces than on hydrophilic. The results revealed that non-lethal concentrations of E. acoroides leaf extract: i) reduce bacterial and fungal coverage by 60.9 and 73.9%, respectively; ii) affect bacterial biofilm maturation and promote dispersion, up to 70%, in fungal biofilm; iii) increase luminescence in Vibrio harveyi by 25.8%. The characterization of methanolic extracts showed the unique profile of the E. acoroides leaf extract. CONCLUSIONS: E. acoroides leaf extract proved to be the most promising extract among those tested. Indeed, the selected non-lethal concentrations of E. acoroides leaf extract were found to exert an antibiofilm effect on C. albicans and E. coli biofilm in the first phase of biofilm genesis, opening up the possibility of developing preventive strategies to hinder the adhesion of microbial cells to surfaces. The leaf extract also affected the dispersion and maturation steps in C. albicans and E. coli respectively, suggesting an important role in cell signaling processes.

Non-Lethal Effects of N-Acetylcysteine on Xylella fastidiosa Strain De Donno Biofilm Formation and Detachment.

This study investigated in-vitro the non-lethal effects of N-acetylcysteine (NAC) on Xylella fastidiosa subspecies pauca strain De Donno (Xf-DD) biofilm. This strain was isolated from the olive trees affected by the olive quick decline syndrome in southern Italy. Xf-DD was first exposed to non-lethal concentrations of NAC from 0.05 to 1000 µM. Cell surface adhesion was dramatically reduced at 500 µM NAC (-47%), hence, this concentration was selected for investigating the effects of pre-, post- and co-treatments on biofilm physiology and structural development, oxidative homeostasis, and biofilm detachment. Even though 500 µM NAC reduced bacterial attachment to surfaces, compared to the control samples, it promoted Xf-DD biofilm formation by increasing: (i) biofilm biomass by up to 78% in the co-treatment, (ii) matrix polysaccharides production by up to 72% in the pre-treatment, and (iii) reactive oxygen species levels by 3.5-fold in the co-treatment. Xf-DD biofilm detachment without and with NAC was also investigated. The NAC treatment did not increase biofilm detachment, compared to the control samples. All these findings suggested that, at 500 µM, NAC diversified the phenotypes in Xf-DD biofilm, promoting biofilm formation (hyper-biofilm-forming phenotype) and discouraging biofilm detachment (hyper-attachment phenotype), while increasing oxidative stress level in the biofilm.