Biofouling and Biofilm Fomation in Engineered Surfaces
- Autores: Blanca Jalvo Sánchez
- Directores de la Tesis: Roberto Rosal García (dir. tes.), Marta Martín Basanta (dir. tes.)
- Lectura: En la Universidad Autónoma de Madrid ( España ) en 2017
- Idioma: inglés
- Número de páginas: 169
- Tribunal Calificador de la Tesis: Ana María Bahamonde Santos (presid.), Francisca Fernández Piñas (secret.), Narges Naseri (voc.), Ana Karina Boltes Espínola (voc.), Maria Soledad Faraldos Izquierdo (voc.)
- Programa de doctorado: Programa Oficial de Doctorado en Microbiología
- Materias:
- Enlaces
- Tesis en acceso abierto en: Biblos-e Archivo
- Resumen
The term fouling refers to the deposition of any undesired material on solid surfaces that leads to some kind of malfunction. The foulant materials can be either organic or inorganic compounds or living organisms. The latter is referred to as biofouling and consists of the accumulation of microorganisms, plants, algae, or animals on exposed surfaces. Biofilms are communities of microorganisms adhering to surfaces, which are embedded by a self-produced extra-polymeric matrix aimed at facilitating their survival in adverse environments. These communities are ubiquitous, occurring in all kinds of environments and pose a number of problems ranging from loss of production efficiency to product spoilage or safety problems.
Bacterial biofilms are a major concern in the development of biomaterials, biomedicine, food industry and filtration systems, among many other fields. Probably, the worst reputation belongs to those affecting the medical and healthcare industries because biofilm-associated organisms are responsible for more than 60% of all microbial infections in humans. Most of the microorganisms have the potential to adhere to and to form biofilms in different surfaces and organs including hospital settings, implants, urinary catheters, teeth or lung tissue, often being responsible for chronic illnesses and hospital-acquired (nosocomial) infections. In most cases, biofilm-related infections are not responsive to conventional antimicrobials and persistently reoccur occasionally leading to life-threatening diseases. In food processing environments, a variety of microorganisms colonize food and survive, grow, and sometimes form multispecies biofilm communities. Once developed, biofilms are a significant potential source of contamination of other products. In water and wastewater treatment facilities, biofilms, fouling and biofouling are ubiquitous and cause corrosion, decreased quality of treated water, and reduced efficacy of filtration systems. Membrane fouling causes a significant decrease in the permeation flux, which results in substantial increases in energy demand, and operational and maintenance costs. In a typical membrane filtration plant, the membrane replacement and membrane cleaning can account for up to 80% of the total operating costs. Due to the adverse impact of biofilms, different physical and chemical methods have been investigated to prevent and remove biofilms. However, the limited success of the strategies followed to prevent biofouling and the emergence of a plethora of new engineered materials, makes it necessary to gain a deeper understanding on the initial steps of microbial colonization and the way of preventing the irreversible formation of biofilms, particularly in the case of new nanostructured surfaces.
The aim of this work was to study the steps of microbial colonization and biofilm formation using the strains Escherichia coli, Pseudomonas putida and Staphylococcus aureus on different engineered substrates, including materials with tunable hydrophilicity and self-cleaning photocatalytic properties. The goal pursued is to determine the conditions required to avoid biofilm attachment by modifying certain surface properties, such as topography and surface chemistry. Several techniques are used for this purpose, which include irradiation treatments with different sources and radiation spectra, namely germicidal ultraviolet sources, with and without emission in the vacuum ultraviolet, and solar radiation simulated with a Xe arc lamp. Other techniques used in this work include the electrohydrodynamic processes electrospray and electrospinning to produce new composite materials with specific antimicrobial and antibiofilm behavior. Electrospray is a method that produces micron sized droplets from a nozzle tip by applying an electric field. In this technique, a suspension flows out from a nozzle forced to disperse into fine droplets by a high voltage source. The size of electrosprayed droplets range from hundreds micrometers down to several tens of nanometer depending on the physical properties of the suspension, the liquid flow rate and the voltage applied between nozzle and collector. While electrospraying refers to the formation of nanoparticles, electrospinning describes the fabrication of fibrous polymer structures. Electrospinning is a versatile procedure for producing polymeric fibers below the micron scale. The technique has been recently investigated in view of its potential to generate high surface-to-volume ratio materials functionalized in the nanoscale. By controlling operating conditions and solution parameters, electrospinning can be used to produce a variety of non-woven porous or smooth nanofibrous structures suitable for their use in filtration processes. There is also the possibility of creating hierarchical structures such as core/shell (coaxial electrospinning) and surface decorated fibers, which allow the electrospinning of non-spinnable substances and complex surface functionalization as well as the improvement of certain properties of the electrospun membranes.
The materials were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and atomic force microscopy (AFM). The physicochemical characteristics of the engineered surfaces were determined by means of surface -potential and X-ray diffraction. The mechanical properties of fibrous polymeric materials were also tested. Confocal microscopy and microplate readings with fluorochromes measuring cell viability or integrity allowed determining the biocidal effect of the materials. For it, the cell-permeant esterase substrate fluorescein diacetate (FDA), the nucleic acid stains SYTO 9 and propidium iodide (PI) were used. In order to visualize the extracellular polymeric matrix, the biofilms were stained with FilmTracer SYPRO Ruby. These methods were complemented by colony counting and the measurement of cell biomass.
New composite materials were successfully prepared using the previously described techniques. The coatings elaborated were, in general, homogeneous layers of tight aggregates of particles displaying planar and fully functional surfaces. The membranes created presented smooth, non-woven and well defined fibers without beading and with diameters of a few hundreds of nanometers. The results showed that the irradiation treatments applied to different functionalized surfaces triggered the transition from a hydrophobic to hydrophilic surface. Such modifications, measured from contact angles, played a determinant role on the initial attachment of bacterial cells to the engineered surfaces. Several studies carried out during this work revealed that bacterial colonization was favored in surfaces with intermediate hydrophilicity whereas hydrophobic or super-hydrophilic surfaces were less prone to bacterial adhesion, irrespective of the surface charge, measured as the zeta potential. On the other hand, the simulation of the solar radiation on the surfaces functionalized with photocatalytic nanoparticles displayed strong biocidal activity in all cases. The conditions for which the elimination of the biofilms formed during dark periods is feasible have been studied. For a certain surface a solar irradiation treatment was able to completely avoid biofilm accumulation keeping the surface free of cells and bacterial exopolymeric matrix. The results are relevant for applications that require enhanced or suppressed biocompatibility of engineered materials.
