The role of bacterial surface components in combination with bacterial functional signals in the process of biofilm formation has been increasingly studied in recent years. Plants support a diverse array of bacteria on or in their roots, transport vessels, stems, and leaves. These plant-associated bacteria have important effects on plant health and productivity. Biofilm formation on plants is associated with symbiotic and pathogenic responses, but how plants regulate such associations is unclear. Certain bacteria in biofilm matrices have been found to induce plant growth and to protect plants from phytopathogens (a process termed biocontrol), whereas others are involved in pathogenesis. In this review, we systematically describe the various components and mechanisms involved in bacterial biofilm formation and attachment to plant surfaces and the relationships of these mechanisms to bacterial activity and survival.

The aims of this work were to study the antimicrobial activity of nine monoterpenes and the synergistic or antagonistic associations between them, and to relate water solubility, H-bonding and pKa values with antimicrobial activity. The minimum inhibitory concentrations (MICs) and minimum bactericidal concentration (MBCs) were determined. The MIC of carvacrol against S. aureus was 3.2 g/l and of thymol was 7.5 g/l. E. coli was resistant. Carvacrol and thymol were bactericidal. The associations geraniol/menthol against S. aureus and B. cereus and thymol/menthol against B. cereus were totally synergistic. Eugenol/geraniol displayed partial synergism against B. cereus. The other groups did not show any synergistic eff ect. Eugenol had the lowest pKa, followed by thymol and carvacrol. Eugenol had the highest total area and polar area and intermolecular and intramolecular hydrogen-bonding capacity, while carvacrol and thymol only had intermolecular hydrogenbonding capacity. The terpenes alone and in combination were eff ective against microorganisms. Phenolic compounds were the most active terpenes. Associations between terpenes were related to the chemical structure. Studies on the antimicrobial activity of associations of terpenes will advance the search for new alternatives for food preservation.

Aims: To evaluate the antifungal activity and to analyse the structure-activity relationship of eleven natural phenolic compounds against four Candida species which are resistant to fluconazole. Methods and Results: Four different species of Candida isolates were used: Candida albicans, Candida krusei, Candida tropicalis and Candida dubliniensis. The phenolic compound carvacrol showed the highest anti-Candida bioactivity, followed by thymol and isoeugenol. The obtained minimum inhibitory concentration (MIC) values obtained were used in a quantitative structureactivity relationship (QSAR) analysis where the electronic, steric, thermodynamic and topological descriptors served as dependent variables. According to the descriptors obtained in this QSAR study, the antifungal activity of phenols has a first action specific character which is based on their interaction with plasma or mitochondrial membranes. The second action is based on a steric descriptorthe maximal and minimal projection of the area-which could explain the inability of some phenolic compounds to be biotransformed to quinones methylene by Candida species. Conclusions: According to the descriptors obtained in this QSAR study, the anti-Candida activity of ortho-substituted phenols is due to more than one action mechanism. The anti-Candida activity of phenolic compounds can be predicted by their molecular properties and structural characteristics. Significance and Impact of the Study: These results could be employed to predict the anti-Candida activity of new phenolic compounds in the search for new alternatives or complementary therapies to combat against candidiasis.

The aim of this work was to evaluate the antibacterial and antifungal activity of essential oils obtained from medicinal plants of the Argentine Republic. The antimicrobial activity of the essential oils of 14 plants collected from different zones was analyzed. The microorganisms used were Staphylococcus aureus, Staphylococcus epidermidis, Bacillus cereus, Micrococcus luteus, Enterococcus faecalis, Escherichia coli, Klebsiella sp., Proteus mirabilis, Pseudomonas aeruginosa, and the yeast Candida albicans. The disk diffusion method was performed to test antimicrobial activity. B. cereus and S. aureus were inhibited by most of the essential oils. Aloysia triphylla, Psila spartoides, and Anemia tomentosa were the most effective compounds against B. cereus, while A. triphylla and Baccharis flabellata were effective against S. aureus. None of the oils inhibited P. aeruginosa. B. flabellata and Pectis odorata were active only against Gram-positive bacteria. A. triphylla and P. spartoides inhibited all tested microorganism, and the remaining essential oils showed variable activity. The minimum inhibitory concentration (MIC) of A. triphylla and P. spartoides essential oils were determined using the disk diffusion method. The lowest MICs were against S. aureus (1=16), B. cereus (1=16), S. epidermidis (1=8), and C. albicans (1=32) for A. triphylla. The lowest MICs were against S. aureus (1=32), B. cereus (1=32), P. mirabilis (1=32), and C. albicans (1=64) with P. spartoides. The results showed that B. cereus and S. aureus were the most sensitive microorganisms, and P. aeruginosa was the most resistant microorganism. This study may contribute to improve ethnobotanical knowledge and would help to discover substances with potential therapeutical uses, as food preservants or as food-borne pathogen inhibitors.

Summary The objective of this study was to evaluate the antimicrobial activity and to study their preserving effect on quality and sensory parameters on flavoured ricotta cheese of Argentinean oregano essential oils (EOs). Criollo essential oil was the most effective agent controlling foodborne bacteria, with MIC values of 1.90 E‐04 mg mL−1 for S. aureus and Salmonella sp. Ricotta with Cordobes essential oil exhibited the lowest percentage of lactic acid at the end of the storage (0.246%). After 30 days of storage, ricotta flavoured with Cordobes and Criollo EOs had the lowest total count (5.63 × 103 and 7.80 × 103 cfu g−1, respectively). The Pearson's correlation analyses (P ≤ 0.05) showed that sour flavour was negatively related to cheese and casein flavours (r = −0.46 and −0.52, respectively). The inclusion of oregano EOs into ricotta cheese improves quality parameters but affects its sensory attributes.

Pseudomonas syringae is a phytopathogenic bacterium that causes lesions in leaves during the colonisation process. The damage is associated with production of many virulence factors, such as biofilm and phytotoxins. The essential oils of Thymus vulgaris (thyme) and Origanum vulgare (oregano) have been demonstrated to inhibit P. syringae. The aim of this study was to investigate the effects of T. vulgaris and O. vulgare essential oils on production of virulence factors of phytopathogenic P. syringae strains, including anti-biofilm and anti-toxins activities. The broth microdilution method was used for determination of MIC and biofilm inhibition assays. Coronatine, syringomycin and tabtoxin were pheno- and genotypically evaluated. Both oils showed good inhibitory activity against P. syringae, with MIC values from 1.43 to 11.5 mg·ml for thyme and 5.8 to 11.6 mg·ml for oregano. Biofilm formation, production of coronatine, syringomycin and tabtoxin were inhibited by thyme and oregano essential oil in most strains. The results presented here are promising, demonstrating the bactericidal activity and reduction of virulence factor production after treatment with thyme and oregano oil, providing insight into how they exert their antibacterial activity. These natural products could be considered in the future for the control of diseases caused by P. syringae.

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