Browsing by Subject "Biofilms"

Now showing 1 - 5 of 5
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    Data supporting the manuscript Role of microbial mats in bed evolution and the formation of sedimentary structures
    (2024-12-05) Assis, Willian; Yang, Judy Q; wassis@umn.edu; Assis, Willian; University of Minnesota, Saint Anthony Falls Laboratory
    This dataset contains the data collected and presented in the manuscript "Role of microbial mats in bed evolution and the formation of sedimentary structures". It includes the bed topographies along the centerline of the channel for each tested case. Additionally, it contains the matlab codes used to process the data.
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    Development of Novel Tools to Study and Combat Pathogenic Microbial Biofilms
    (2014-12) Erickson, Joshua
    An increase in antibiotic resistance along with a decrease in antimicrobial products coming to market has compounded into a global issue that must be addressed. Biofilms are a morphological state of many pathogenic microbes that significantly augments their resistance to antimicrobial agents. Today, there is a need not only for groundbreaking strategies that are effective against drug resistant pathogens in their biofilm form, but also for tools to efficiently grow reproducible biofilms for development of anti-biofilm products. In this work, the design of a novel reactor for biofilm testing and the development of a model live biotherapeutic product that targets and delivers antimicrobial products to specific biofilms are described. The biofilm reactor is a high-throughput laminar flow reactor that is capable of producing uniform biofilm on surfaces for efficient subsequent testing. The live biotherapeutic is an engineered strain of Lactococcus lactis that specifically attaches to Pseudomonas aeruginosa biofilm structures using surface display technology. Preliminary testing was performed to characterize the anti-biofilm properties of multiple wild-type lactic acid bacteria (LAB) strains in order to choose the most effective strains for further development of the anti-biofilm component.
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    Electrical current generation by wild type and mutant Shewanella strains
    (2009-12) Baron, Daniel Benjamin
    The genus Shewanella has been reported to have the capacity to couple the transfer of electrons to insoluble metal oxides and solid carbon electrodes with cellular growth. While this process may be useful as an energy generation strategy or biotechnological tool, the electron transfer pathway by which this process occurs is not completely understood, and better techniques for studying the transfer mechanism are needed. This project used single chamber electrochemical cells to show that the current generation capabilities of Shewanella oneidensis are dependent on the ability of cells comprising a biofilm to shuttle soluble electron carriers between an electrode and its outer membrane cytochromes. The extracellular electron transfer capabilities of S. oneidensis mutant strains containing deleted or transposon-interrupted copies of genes known to be involved in extracellular electron transfer were also studied and compared to wild type. Amperometry was utilized to monitor real-time electron flow between attached anaerobic wild type and mutant cells and a poised carbon working electrode. Differential pulse voltammetry and cyclic voltammetry performed on electrode attached S. oneidensis MR-1 wild type cells detected both mediated and direct electron transfer reactions at the electrode surface. Ion exchange HPLC verified the presence of endogenously produced flavin compounds in S. oneidensis liquid cultures and confirmed the most common flavin in S. oneidensis MR-1 electrochemical cell analytes is riboflavin (vitamin B2). It was also discovered that removing the medium surrounding an electrode biofilm caused current production from the electrochemical cell to decrease. Returning the filtered original medium, or adding anaerobic riboflavin resulted in the restoration of current production. The amount of current produced at the carbon working electrode increased with biofilm development and accumulation of soluble electron mediator. A correlation was observed between the concentration of the redox shuttle in potentiostat-controlled electrochemical cells and the maximum sustainable current, as well as maximum electrode biofilm thickness. For example, wild type cultures with twice the natural amount of riboflavin approximately doubled their electrode current production and also attached to the electrode in larger numbers. Electrode phenotypes of Shewanella oneidensis MR-1 mutant strains were also observed and compared to wild type. The deletion of several genes, such as for the outer membrane cytochrome MtrC, the periplasmic cytochrome MtrA, or the membrane beta barrel protein MtrB severely impaired MR-1 cells from attaching to the carbon electrode. As a result, the deletion mutant strains were incapable of producing significant anodic current and were deficient in electrode attached biomass. However, deletion of the outer membrane cytochrome OmcA, or genes related to the formation of mature biofilms resulted in a percentage of the current production being retained. This data supports the theory that MtrC is a key component in the terminal electron transfer step for S. oneidensis MR-1 cells interacting with solid surfaces. Measurements of current production from MR-1 electrode biofilms revealed that the extracellular electron transfer process involves both cell associated enzymes and flavins acting as soluble electron transfer agents. However, these separate pathways most likely utilize many of the same, membrane proteins to accomplish their function. This study indicates it is likely that the deposition of electrons by S. oneidensis MR-1 to a poised electrode can be done both directly by MtrC while stabilized or otherwise assisted by other outer membrane elements such as OmcA or MtrB, as wells as through cycling of redox active shuttles such as flavins between MtrC and the electrode surface. As a result, for electrode attached Shewanella oneidensis MR-1 cells, a complex relationship exists between soluble flavin concentration, biofilm thickness, and electrical current production. These factors pertain greatly to the capabilities and limitations of S. oneidensis, especially while functioning as part of a electrochemical device, and must be taken into account when utilizing this organism for research or other applications.
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    Evaluating the antimicrobial mechanism of neutral electrochemically activated water on foodborne pathogens and their biofilms
    (2012-12) Yang, Hongshun
    Sanitizing is a key step in ensuring food safety. Neutral electrochemically activated water (NECAW) not only has antimicrobial effects but also is relatively friendly to handlers and foods, and it complies with organic food practices. However, its antimicrobial effects on different pathogens and strains have not been examined and its antimicrobial mechanisms are not fully understood. The goal of this project was to investigate the use of NECAW as a sanitizer in inactivating foodborne pathogens. The first objective of this study was to determine the effectiveness and broadspectrum activity of NECAW against foodborne pathogens. The sanitizing efficacy of NECAW against 40 different strains of E. coli O157:H7, L. monocytogenes, and Salmonella as liquid cultures, dried cells on stainless steel (SS) surfaces, and biofilms on SS was examined. It was found that NECAW with 100 mg/l free available chlorine (FAC) caused more than 5 log CFU/ml reductions for all strains in liquid culture, more than 3 log CFU/coupon reductions for 92.5% of the strains dried on stainless steel (SS) surfaces and for 27.5% of biofilms. Among all the strains, S. Newport B4442CDC was the most resistant strain to NECAW on surfaces while E. coli O157:H7 ATCC 43895 was the most resistant strain in biofilms and liquid pure cultures. Overall, NECAW was effective and had a broad-spectrum activity against foodborne pathogens. The second objective was to evaluate the sanitizing effect of NECAW and other commercial ‘active water’ technologies on foodborne pathogens. Five individual strains of each foodborne pathogen including E. coli O157:H7, L. monocytogenes, and Salmonella as liquid cultures and dried cells on stainless steel surfaces were studied by iv comparing the sanitizing effect of NECAW and available commercial technologies on these pathogens. The results showed that 100 mg/l ECAW had sanitizing effects of at least 5 log CFU/ml reductions on liquid culture and more than 4 log CFU/coupon reductions for pathogens dried on SS surfaces. In contrast, the other commercial technologies tested were not effective in sanitizing. They, however, washed the bacteria off the surface into rinse water, which would lead to a significant safety concern of cross contamination. The third objective of this study was to examine the three dimensional morphology of foodborne pathogen biofilms using atomic force microscopy (AFM). AFM experiments were conducted by directly imaging the three-dimensional morphology of the foodborne pathogens biofilms (five strains for each pathogen), and imaging the biofilms pre- and post-NECAW treatment. Images of AFM showed tree-like structures as well as individual cells. L. monocytogenes biofilms had a higher percentage of tree-like structures than E. coli O157:H7 and Salmonella. The biofilm structures and microbial cells on SS were destroyed by the treatment with NECAW according to the AFM study, providing morphological evidence that NECAW was effective in controlling surface contamination of pathogenic bacteria and biofilm growth. The fourth objective of this study was to assess the role of sigB and inlA genes in L. monocytogenes biofilm formation and the antimicrobial efficacy of NECAW treatment on L. monocytogenes. The expression levels of sigB and inlA genes were investigated by using qPCR, and sanitizing effects of NECAW on wild-type (WT) and sigB/inlA mutant L. monocytogenes strains were determined by the direct plating method. After NECAW v treatment, expression of both genes increased for the WT. While sigB gene expression of the ΔinlA strain increased to a level comparable to that of the WT, inlA gene expression of the ΔsigB strain did not significantly increase. Both genes were expressed more in biofilms than in liquid cultures. The level of inlA gene expression in WT increased by 4.28 and 5.51-fold by treatment with 4 mg/l NECAW for 10 min in liquid cultures and biofilms, respectively, while the corresponding values were 5.91 and 10.05-fold for the sigB gene. Mutant strains were more sensitive to NECAW treatment than the WT strain. The sigB gene was more important than inlA for the pathogen’s survival under NECAW treatment. Surviving L. monocytogenes cells post-sublethal NECAW treatment might become resistant to further sanitizer treatment.
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    The role of Enterococcus faecalis biofilm formation in the regulation of conjugation.
    (2012-06) Cook, Laura Carol Case
    Enterococcus faecalis has recently emerged as an important nosocomial pathogen. Pathogenicity of these organisms depends greatly on a few important aspect of enterococcal physiology. The ability of enterococci to form biofilms greatly enhances their virulence. Their innate resistance to many antibiotics and their ability to transfer these resistance genes through conjugation heightens their threat to human health. The work described in this thesis attempts to explain the roles of biofilm growth, conjugation, and cell communication in E. faecalis. To examine the role of biofilm growth on the E. faecalis transcriptome, RNAseq analysis was undertaken. We found that over 100 genes were measurably upregulated during biofilm growth while approximately 26 genes were downregulated. These data gives us important insights into the biology of enterococcal biofilms. In clinical settings, biofilms are likely locations for antibiotic resistance transfer events involving nosocomial pathogens such as E. faecalis. Conjugation is an important mode of horizontal gene transfer in bacteria, enhancing the spread of antibiotic resistance. In this work, I demonstrate that growth in biofilms alters the induction of conjugation by a sex pheromone in E. faecalis. Mathematical modeling suggested that a higher plasmid copy number in biofilm cells would enhance a switch-like behavior in the pheromone response of donor cells with a delayed, but increased response to the mating signal. Alterations in plasmid copy number and a bimodal response to induction of conjugation in populations of plasmid-containing donor cells were both observed in biofilms, consistent with the predictions of the model. The pheromone system may have evolved such that donor cells in biofilms are only induced to transfer when they are in extremely close proximity to potential recipients in the biofilm community. These results have important implications for development of chemotherapeutic agents to block resistance transfer and treat biofilm-related clinical infections.