Showing papers on "Biofilm published in 1984"

Activity of Pseudomonas aeruginosa in biofilms: Steady state

Abstract: Aerobic glucose metabolism by Pseudomonas aeruginosa in steady-state biofilms at various substrate loading rates and reactor dilution rates was investigated. Variables monitored were substrate (glucose), biofilm cellular density, biofilm extracellular polymeric substance (EPS) density, and suspended cellular and EPS concentrations. A mathematical model developed to describe the system was compared to experimental data. Intrinsic yield and rate coefficients included in the model were obtained from suspended continuous culture studies of glucose metabolism by P. aeruginosa. Experimental data compared well with the mathematical model, suggesting that P. aeruginosa does not behave differently in steady-state biofilm cultures, where diffusional resistance is negligible, than in suspended cultures. This implies that kinetic and stoichiometric coefficients for P. aeruginosa derived in suspended continuous culture can be used to describe steady-state biofilm processes.

The Etiology and Persistence of Cryptic Bacterial Infections: A Hypothesis

Abstract: The growth and survival mechanisms used by Pseudomonas aeruginosa in human infections are similar to those used by the organism in aquatic systems. P. aeruginosa attaches to inert solid or tissue surfaces and grows predominantly in biofilms that release mobile swarmer cells into the surrounding fluid phase. These natural and pathogenic biofilms are covered by an exopolysaccharide matrix (glycocalyx) that serves as a barrier against hostile environmental factors, such as host defense mechanisms and antibiotics. Glycocalyx-enclosed biofilms of P. aeruginosa or other bacteria have been identified in experimental or clinical infections arising from contaminated prostheses and in chronic refractory infections, such as endocarditis, osteomyelitis, and P. aeruginosa pneumonia associated with cystic fibrosis. Conventional in vitro antibiotic susceptibility tests are directed against unprotected, mobile, swarmer cells. Antibiotics used to treat sequestered infections should be tested against populations of pathogens in intact biofilms to determine the ability of the antibiotics to penetrate the glycocalyces and to kill the component bacteria.

Biofilm Development: A Process Analysis

Abstract: This paper will provide a framework for understanding the process of biofilm development in the context of stoichiometry and kinetics Biofilm development is described in terms of selected fundamental rate processes and environmental parameters which influence their rate and extent The properties of the biofilm and its microenvironment lead to topics of microbial ecology within the biofilm and the physiology of the organisms immobilized within it These topics will be discussed in terms of unstructured models for the microbial processes

Comparative Physiology of Attached and Free-living Bacteria

Abstract: The environmental conditions at a solid-liquid interface differ from those in the bulk aqueous phase, and, accordingly, the physiological activity of bacteria attached to surfaces may differ from that of free living cells. There are three principal ways in which environmental conditions at a solid surface may influence the physiology of attached cells. First, nutrient concentration and/or accessibility may be different at the interface because of adsorption or irreversible binding of low molecular weight or macromolecular substrates. Second, processes, e.g., substrate transport and energy generation, which are sited in the cell membrane and which are central to all physiological processes, may be modified by elastic deformation of the cell envelope. Third, surfaces provide a site for colonization and the development of a bacterial biofilm, in which cells are embedded in a polymeric matrix. Such a colony microenvironment allows interactions between resident organisms, which frequently include a range of functional types, and affords protection from outside perturbations or lethal agents. Experimental measurements of the effects of solid surfaces on the activity of associated bacteria have varied considerably. The type of result obtained, ranging from promotion to inhibition of activity, has depended upon the type of activity measured, the organism, the substrate and/or its concentration, and the chemical composition of the substratum.

Methanogenic activity and structural characteristics of the microbial biofilm on a needle-punched polyester support.

Abstract: In a downflow stationary fixed-film anaerobic reactor receiving a swine waste influent, few bacteria were observed to be tightly adherent to the surfaces of the needle-punched polyester support material. However, there was a morphologically complex, dense population of bacteria trapped within the matrix. Frequently large microcolonies of a uniform morphological type of bacteria were observed. These were particularly evident for methanosarcina-like bacteria which grew forming large aggregates of unseparated cells. Leafy deposits of electron-dense, calcium- and phosphorus-enriched material coated the polyester matrix and some cells. As the biofilm matured there was more extensive mineral deposition which completely entrapped cells. The entrapped cells appeared to autolyze, and many were partially degraded. Further impregnation of the matrix with minerals and apparent cell death may eventually have a deleterious effect on the methanogenic activity of the biofilm. Images

Chemical Characterization of Films

Abstract: Biofilms represent a complex assembly of different groups of attached microbes with their excretory products. Sensitive measures of the biomass, community structure, nutritional status, and metabolic activities, as well as the chemical characterization of their extracellular polymers, have given insight into the ecology of this system. Exposure of surfaces to flowing waters produces a succession of microbes whose community structure and metabolic activity is affected by the chemistry, biodegradability, and microtopography of the surface, as well as the shear forces and nutrient content of the flowing waters. The grazing of the biofilm by predators or the mechanical or chemical disruption of the biofilm greatly affect the metabolic activity and the potential for secondary reaccumulation and the secretion of extracellular polymers. The extracellular polymers formed by the biofilm microbes are particularly important as they greatly increase the resistance of the microbes to biocides and the efficiency of heat transfer. The metabolic activity of thin biofilm can create microanaerobic sites that facilitate the growth of fermenters and hydrogen utilizers whose acidic fermentation products can greatly facilitate corrosion. The microanalytical methods currently available require the destruction of the biofilm in its assay. With progress in instrumentation the destructive sampling can be supplanted by nondestructive continuous monitoring, possibly utilizing a Fourier transforming infrared system which may provide insights into the chemical basis of adhesion and interactions between the components of the biofilm microbial assembly.

Microbial adhesion and aggregation : report of the Dahlem Workshop on Microbial Adhesion and Aggregation, Berlin 1984, January 15-20

Abstract: Mechanisms of Adhesion.- Physicochemical Interactions of the Substratum, Microorganisms, and the Fluid Phase.- Stereo-biochemistry and Function of Polymers.- Adhesion to Inanimate Surfaces.- Adhesion to Animal Surfaces.- Bacterial Adhesion to Plant Root Surfaces.- Genetic Control of Bacterial Adhesion.- Biofilm Development and Its Consequences.- Surface Colonization Parameters from Cell Density and Distribution.- Biofilm Development: A Process Analysis.- Chemical Characterization of Films.- Effects of Network Structure on the Phase Transition of Acrylamide-Sodium Acrylate Copolymer Gels.- Colonization by Higher Organisms.- Activity on Surfaces.- Comparative Physiology of Attached and Free-living Bacteria.- Activities of Microorganisms Attached to Living Surfaces.- Utilization of Substrates and Transformation of Solid Substrata.- Attachment of Bacteria: Advantage or Disadvantage for Survival in the Aquatic Environment.- Aggregation.- Physiology of Cell Aggregation: Flocculation by Saccharom yces cerevisiae As a Model System.- Aggregation, Cohesion, Adhesion, Phagocytosis, and Morphogenesis in Dictyostelium - Mechanisms and Implications.- Consequences of Aggregation.- Microcolony Formation and Consortia.- Epilogue.- List of Participants with Fields of Research.- Author Index.

Biological-particulate fouling interactions: effects of suspended particles on biofilm development

Abstract: The effect of suspended solids on fouling biofilm development was investigated using kaolin particles (2–5μm) and the bacterium Pseudomonas fluorescens as the model system. At a flow velocity of 1.2ms–1, 50 mg 1–1 kaolin significantly extended the lag phase of biofilm growth. After exposure for up to 48 hours attached cell numbers were only 8% of the control values with no kaolin present. Despite this initial inhibition the biofilm weight increase was ultimately greater in the presence of the particles, presumably due to a stimulation of attached cell growth or to the entrapment of kaolin within the attached cell matrix, or both. The implications of these observations for foulant control and plant operation are discussed.

Estimation of the biofilm formation ability of Pseudomonas putida in discrete samples from continuous culture

Abstract: Test systems were set up in order to evaluate the ability of biomass from a continuous culture to form biofilms. A film-forming strain of Pseudomonas putida was used as the test organism. The adsorption of resting cells onto glass surfaces was measured in specially designed chambers containing 1 ml of cell suspension. Both the quantity and the physiological activity of the adsorbed cells, in terms of optical density after detachment and pH change of a substrate exposed to the adsorbed cells, were measured. The analysis of biomass from continuous cultures of Pseudomonas putida verified the suitability of the methods. Furthermore, other properties of importance to biofilm formation such as hydrophobicity and flocculation capacity of the cells were investigated.