Biofilm-Forming Ability of Phytopathogenic Bacteria: A Review of its Involvement in Plant Stress.

Phytopathogenic bacteria not only affect crop yield and quality but also the environment. Understanding the mechanisms involved in their survival is essential to develop new strategies to control plant disease. One such mechanism is the formation of biofilms; i.e., microbial communities within a three-dimensional structure that offers adaptive advantages, such as protection against unfavorable environmental conditions. Biofilm-producing phytopathogenic bacteria are difficult to manage. They colonize the intercellular spaces and the vascular system of the host plants and cause a wide range of symptoms such as necrosis, wilting, leaf spots, blight, soft rot, and hyperplasia. This review summarizes up-to-date information about saline and drought stress in plants (abiotic stress) and then goes on to focus on the biotic stress produced by biofilm-forming phytopathogenic bacteria, which are responsible for serious disease in many crops. Their characteristics, pathogenesis, virulence factors, systems of cellular communication, and the molecules implicated in the regulation of these processes are all covered.

Hexanic extract of Achyrocline satureioides: antimicrobial activity and in vitro inhibitory effect on mechanisms related to the pathogenicity of Paenibacillus larvae.

INTRODUCTION: Paenibacillus larvae is a spore-forming bacillus, the most important bacterial pathogen of honeybee larvae and the causative agent of American foulbrood (AFB). Control measures are limited and represent a challenge for both beekeepers and researchers. For this reason, many studies focus on the search for alternative treatments based on natural products. AIM: The objective of this study was to determine the antimicrobial activity of the hexanic extract (HE) of Achyrocline satureioides on P. larvae and the inhibitory activity on some mechanisms related to pathogenicity. MATERIAL AND METHODS: The Minimum Inhibitory Concentration (MIC) of the HE was determined by the broth microdilution technique and the Minimum Bactericidal Concentration (MBC) by the microdrop technique. Swimming and swarming motility was evaluated in plates with 0.3 and 0.5% agar, respectively. Biofilm formation was evaluated and quantified by the Congo red and crystal violet method. The protease activity was evaluated by the qualitative technique on skim milk agar plates. RESULTS: It was determined that the MIC of the HE on four strains of P. larvae ranged between 0.3 and 9.37 µg/ml and the MBC between 1.17 and 150 µg/ml. On the other hand, sub-inhibitory concentrations of the HE were able to decrease swimming motility, biofilm formation and the proteases production of P. larvae.

Fractionation of hexane extracts from Achyrocline satureioides and their biological activities against Paenibacillus larvae.

Previous studies carried out in our laboratory described the antimicrobial activity of the whole hexanic extract (HE) of Achyrocline satureioides (Lam.) DC against Paenibacillus larvae, the causal agent of American Foulbrood (AFB) a disease of the honey bee larvae. In this study, the HE was partitioned into five main fractions by chromatographic techniques leading to the isolation of four known compounds: two prenylated phloroglucinol α-pyrones (1 and 3), 5,7-dihydroxy-3,8-dimethoxyflavone (gnaphaliin A) (2), and 23-methyl-6-O-demethylauricepyrone (4). Isolated compounds were further analyzed towards structural elucidation using 1H RMN and 13C RMN spectroscopic techniques. For the first time, the antimicrobial activity of the isolated compounds was evaluated against P. larvae strains by broth microdilution method and compared with that of the whole HE. Compounds 1-4 displayed minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) values ranging between 0.07 and 62.5 µg/mL and 0.26 and 12.5 µg/mL, respectively. The lowest MIC and MBC values were obtained with compounds 3 and 4, respectively. The antimicrobial activity of each single compound and the combination of them showed that the presence of all compounds is needed for the antimicrobial efficacy of whole HE.

The role of bacterial biofilms and surface components in plant-bacterial associations.

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.

Antimycotic effect of the essential oil of Aloysia triphylla against Candida species obtained from human pathologies.

The research of alternative substances to treat infections caused by Candida species is a need. Aromatic plants have the ability to produce secondary metabolites, such as essential oils (EO). The antimicrobial properties of Aloysia triphylla (L'Her.) Britton (cedrón) EO has been previously described. The aims of this work were to determine the antimicrobial activity and the effect on the cell structure of the EO of A. triphylla against Candida sp isolated from human illnesses. The EO was obtained by hydrodistillation of A. triphylla leaves. The minimum inhibitory concentration (MIC) was performed with microdilution method and the minimum fungicidal concentration (MFC) was determined. A. triphylla EO's showed antifungal activity against all yeast: C. albicans, C. dubliniensis, C. glabrata, C. krusei, C. guillermondii, C. parapsilosis and C. tropicalis which were resistant to fluconazol (150 mg/mL). The range of MIC values was from: 35 to 140 microg/mL and the MFC: 1842 to 2300 microg/mL. The time of killing at the MFC against C. albicans (3 x 10(5) UFC/mL) was 140 min. The dates of OD620 and OD260 suggest lysis and loss of absorbing material, respectively. The HROM shows distortion in morphology and shape of the cell, with large vacuoles in the cytoplasm. These studies clearly show that A. triphylla EO is a promising alternative for the treatment of candidiasis.