BackgroundMicroorganisms of different species interact in several ecological niches, even causing infection. During the infectious process, a biofilm of single or multispecies can develop. Aspergillus fumigatus and Staphyloccocus aureus are etiologic agents that can cause infectious keratitis. We analyzed in vitro single A. fumigatus and S. aureus, and mixed A. fumigatus-S. aureus biofilms. Both isolates were from patients with infectious keratitis. Structure of the biofilms was analyzed through microscopic techniques including scanning electron microscopy (SEM), transmission electron microscopy (TEM), confocal, and fluorescence microscopy (CLSM) in mixed biofilm as compared with the single A. fumigatus biofilm.ResultsTo our knowledge, this is the first time that the structural characteristics of the mixed biofilm A. fumigatus-A. fumigatus were described and shown. S. aureus sharply inhibited the development of biofilm formed by A. fumigatus, regardless of the stage of biofilm formation and bacterial inoculum. Antibiosis effect of bacterium on fungus was as follows: scarce production of A. fumigatus biofilm; disorganized fungal structures; abortive hyphae; and limited hyphal growth; while conidia also were scarce, have modifications in their surface and presented lyses. Antagonist effect did not depend on bacterial concentration, which could probably be due to cell-cell contact interactions and release of bacterial products. In addition, we present images about the co-localization of polysaccharides (glucans, mannans, and chitin), and DNA that form the extracellular matrix (ECM). In contrast, single biofilms showed extremely organized structures: A. fumigatus showed abundant hyphal growth, hyphal anastomosis, and channels, as well as some conidia, and ECM. S. aureus showed microcolonies and cell-to-cell bridges and ECM.ConclusionsHerein we described the antibiosis relationship of S. aureus against A. fumigatus during in vitro biofilm formation, and report the composition of the ECM formed.

Palabras clave: metales pesados, cultivo in vitro, peroxidasas, hemoperoxidasas, respuesta antioxidante RESUMEN Se propone el proceso de biotización como una nueva técnica para el cultivo de tejidos vegetales que permite la asociación entre plantas y microorganismos en condiciones in vitro. A la inoculación de tejido calloso cultivado in vitro se le denomina bacterización, proceso en que las bacterias estimulan el crecimiento de las plántulas e inducen cambios en su desarrollo, lo que les permite potenciar sus mecanismos de respuesta ante el estrés. Uno de los efectos más notables en las plantas expuestas a cadmio es el incremento o disminución de las enzimas antioxidantes, con la posible participación de las fenoloxidasas. El presente trabajo evaluó la respuesta de cultivos de callo de Epithelantha micromeris (Engelm.) inoculados con rizobacterias promotoras del crecimiento vegetal, a través de la actividad de guaiacol peroxidasas y hemoperoxidasas como respuesta al estrés oxidativo producido por la exposición a cadmio. De los resultados obtenidos, la presencia de las rizobacterias per se ocasionó una condición de estrés; no obstante, en presencia de cadmio se indujo una respuesta antioxidante que incluyó el incremento de fenoloxidasas, indicadoras de estrés oxidativo. ABSTRACTA biotization process is proposed as a new technique in plant tissue culture that allows in vitro the association between plants and microorganisms. Bacterization is the inoculation of callus tissue cultivated in vitro. In this process, bacteria promote the plants growth, induce changes in their development and increase the response mechanisms against stress conditions. One of the most notable effects of plants exposed to cadmium is the increment or inhibition of antioxidant enzymes, with the possible participation of phenoloxidases. The present study evaluated the response of callus tissue of Epithelantha micromeris

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