Biofilm Formation and Structure
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Questions and Answers

What does the Most Probable Number (MPN) method estimate?

  • The total turbidity of a liquid sample
  • The size of bacterial colonies on a plate
  • The number of viable microorganisms in a sample (correct)
  • The average generation time of microorganisms
  • Which of the following best describes coliform bacteria?

  • Bacteria that indicate water is safe for drinking
  • Non-pathogenic bacteria exclusively found in soil
  • Lactose-fermenting bacteria that signal potential water contamination (correct)
  • Bacteria that do not ferment lactose
  • In the MPN method, how many tubes showed growth in the 1-mL dilution?

  • No tubes showed growth
  • All tubes showed growth
  • 2 out of 5 tubes showed growth (correct)
  • 1 out of 5 tubes showed growth
  • What is the purpose of the pH indicator in lactose broth during the MPN method?

    <p>To change color when lactose is fermented, indicating growth</p> Signup and view all the answers

    What does a high turbidity in a liquid bacterial culture indicate?

    <p>High cell density of microorganisms</p> Signup and view all the answers

    Which dilutions in the MPN method showed positive growth results?

    <p>10 mL and 1 mL</p> Signup and view all the answers

    Which environmental factor can influence microbial growth in the MPN method?

    <p>pH of the lactose broth</p> Signup and view all the answers

    What term describes the time it takes for cells to divide?

    <p>Intrinsic growth rate</p> Signup and view all the answers

    How is the estimated number of bacteria derived from the MPN results?

    <p>Using a mathematical formula based on growth observations</p> Signup and view all the answers

    During which phase do cells become less sensitive to antibiotics?

    <p>Stationary phase</p> Signup and view all the answers

    Which factor primarily causes the growth to slow in the stationary phase?

    <p>Nutrient depletion</p> Signup and view all the answers

    What is the main purpose of using a chemostat in microbial growth?

    <p>To provide a consistent nutrient supply</p> Signup and view all the answers

    Which staining method differentiates between live and dead cells?

    <p>Viability staining</p> Signup and view all the answers

    What does the direct microscopic cell count method use for counting cells?

    <p>Petroff-Hausser chamber</p> Signup and view all the answers

    Which type of cells may survive during the death phase and potentially cause chronic infections?

    <p>Persister cells</p> Signup and view all the answers

    In what condition is the intrinsic growth rate predominantly measured?

    <p>In a closed culture system</p> Signup and view all the answers

    What role does the extracellular polymeric substance (EPS) play in a biofilm's structure?

    <p>It maintains the biofilm's structure and keeps it hydrated.</p> Signup and view all the answers

    During the initial stages of biofilm formation, what characterizes the attachment of planktonic cells?

    <p>The binding starts reversible before becoming permanent.</p> Signup and view all the answers

    How do microorganisms within a biofilm collaborate metabolically?

    <p>Waste from one species serves as a nutrient for another.</p> Signup and view all the answers

    What mechanism allows bacteria in biofilms to sense their population density?

    <p>Quorum sensing through autoinducers.</p> Signup and view all the answers

    What is a significant effect of biofilms on human health?

    <p>They can support the development of dental plaque and infections.</p> Signup and view all the answers

    What is a common resistance mechanism found in pathogens within biofilms?

    <p>Metabolically inactive cells in deeper biofilm layers.</p> Signup and view all the answers

    Which structures facilitate the interaction of cells with the extracellular polymeric substances (EPS) in mature biofilms?

    <p>Fimbriae, pili, and flagella.</p> Signup and view all the answers

    What is a potential drawback of biofilms in medical devices?

    <p>They can clog devices and compromise their functionality.</p> Signup and view all the answers

    Study Notes

    Biofilms Overview

    • Biofilms in slow-moving water exhibit a mushroom-like shape and contain clusters of microorganisms.
    • Extracellular polymeric substances (EPS) comprise 50%-90% of biofilm mass, primarily made of polysaccharides, proteins, nucleic acids, and lipids.
    • EPS maintains biofilm structure, ensures hydration, and protects microorganisms from predation.

    Biofilm Formation

    • Planktonic cells attach to surfaces and transition to sessile cells.
    • Initial attachment is reversible, but cells soon produce EPS, solidifying the connection.
    • Water channels develop within the biofilm matrix, facilitating nutrient and waste exchange.
    • Structures such as fimbriae, pili, and flagella are pivotal in forming mature biofilms.
    • Cells can later revert to planktonic states, spreading to colonize new areas.

    Biofilm Dynamics

    • Inter-microorganism collaboration allows for mutual benefit; waste from one can feed another.
    • Aerobic organisms generate anaerobic zones, supporting anaerobic species.

    Quorum Sensing

    • Microbial communication occurs through quorum sensing, utilizing autoinducers to gauge population density.
    • Upon reaching critical density, genes that enhance survival are activated, including those aiding pathogen immunity evasion.

    Communication Molecules

    • Gram-negative bacteria employ N-acylated homoserine lactones for communication.
    • Gram-positive bacteria use small peptides, leading to signaling cascades that modify gene expression.

    Impact on Human Health

    • Biofilms can be beneficial (e.g., gut microbiota) or detrimental (e.g., dental plaque, infections).
    • Pathogenic biofilms, such as those formed by Pseudomonas aeruginosa, exhibit heightened antibiotic resistance due to:
      • Metabolically inactive cells in deeper layers.
      • EPS hindering antibiotic penetration.
      • Enhanced efflux pumps expelling antibiotics from cells.
      • Horizontal gene transfer for antibiotic resistance among biofilm members.

    Biofilms in Medical Devices and Equipment

    • Biofilms can impede functioning of devices like CPAP machines and ISS filtration systems.
    • The intrinsic growth rate denotes the time required for cell division; growth is exponential.
    • Exponential growth phases are critical for industrial applications as cells are most vulnerable to disinfection.

    Stationary Phase

    • Growth deceleration occurs due to nutrient depletion and waste buildup, leading to a stable population.
    • Organisms may enter survival mode, reducing antibiotic sensitivity, with some producing spores and virulence factors.

    Death Phase

    • Nutrient exhaustion and toxic waste lead to cell death outpacing division.
    • Some surviving cells can form endospores or "persister" cells that maintain low metabolism, potentially causing chronic infections.

    Sustaining Microbial Growth

    • Chemostats support continuous microbial growth in closed systems by providing nutrients and removing waste, keeping cells in a log phase.

    Measurement of Bacterial Growth

    • Bacterial count assesses cell quantity in samples; important for clinical infection levels and contamination control in various sectors.
    • Direct methods involve physical counting, while indirect methods gauge activity or presence without actual counting.

    Direct Cell Count

    • Methods like direct microscopic count using calibrated slides allow for quick assessments of cell concentrations.
    • Limitations include ineffectiveness for dilute samples and inability to differentiate between live and dead cells.

    Fluorescence Staining

    • Viability stains identify live (green) versus dead (red) cells.
    • Most Probable Number (MPN) method statistically estimates viable microorganisms, especially useful for low-concentration samples in food and water.

    Coliform Bacteria and MPN Method

    • Coliforms indicate water contamination, especially from fecal matter.
    • MPN involves diluting water samples and monitoring fermentation growth in lactose broth, with pH indicators signifying result.
    • Results are interpreted using probability tables to estimate concentrations in water, e.g., 49 bacteria per 100 mL.

    Indirect Cell Counts

    • Turbidity measures indicate bacterial density; spectrophotometers facilitate this by analyzing light transmission through samples.

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    Bacterial Growth Curve PDF

    Description

    Explore the fascinating world of biofilms and discover how they form in slow-moving water. This quiz covers the characteristics of biofilms, including their mushroom-like shapes, the role of extracellular matrix (EPS), and the significance of polysaccharides in maintaining structure and hydration.

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