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Microbial Growth and Environmental Influences

  • Medical Biofilms

    • Biofilms are thin layers of microorganisms embedded in a matrix material, often contaminating medical devices.
    • Example: Staphylococcus aureus bacteria are shown attached to catheter walls in an electron micrograph.
    • Biofilms provide a protected environment for microorganisms, aiding in their colonization and resisting cleaning efforts.
    • Clinical significance includes plaque on teeth, infections in cystic fibrosis patients, and endocarditis.

  • Biofilm Formation and Environmental Impact

    • Biofilms have been found on the International Space Station, causing issues with equipment and potentially threatening long-term space missions.
    • Research indicates methods for biofilm prevention through surface preparations to hinder microbial adhesion.

  • Learning Objectives Involved

    • Define generation time and binary fission.
    • Describe microbial growth phases: lag, log, stationary, and death phases.
    • Explain laboratory techniques for cell counting and biofilm characteristics.
    • Identify health risks associated with biofilms and discuss quorum sensing.

  • The Bacterial Cell Cycle

    • Bacterial reproduction mainly occurs through binary fission.
    • Process includes DNA replication and partitioning into daughter cells.
    • FtsZ protein plays a significant role as it forms a Z ring in cell division; the divisome structure activates to form a division septum.

  • Generation Time

    • Defined as the time it takes for a population to double.
    • Varies between species:
      • E. coli: ~20 minutes in optimal conditions.
      • M. tuberculosis: 15-20 hours.
      • M. leprae: 14 days.

  • Calculating Cell Numbers

    • The number of cells can be modeled mathematically by 2^n , where n is the number of divisions.
    • An initial example of one cell dividing every 30 minutes can lead to a vast population size after 24 hours by using scientific notation for large numbers.

  • Microbial Growth Phases

    • Lag Phase: Initial adjustment with no change in cell number but increased metabolic activity.
    • Log Phase: Rapid growth with constant metabolic activity; cells are most susceptible to antibiotics.
    • Stationary Phase: Growth rate slows due to resource limitations; number of new cells equals the number of dying cells.
    • Death Phase: Fatal conditions result in more cells dying than being created.

  • Lab Techniques for Counting Cells

    • Direct Cell Count: Using a Petroff-Hausser chamber for microscopic counting.
      • May not distinguish between live and dead cells effectively without viability staining methods.
    • Electronic Counters: Coulter counter detects cells by measuring resistance changes without differentiating live or dead cells.
    • Viable Plate Count: Counts CFUs based on colony growth from viable cells.
    • Most Probable Number (MPN): Statistical method used for very dilute samples.
    • Turbidity Measurement: Estimating bacterial density through spectrophotometry correlates absorbance with cell concentration.

  • Biofilm Formation Steps

    • Initial adhesion of free-floating planktonic cells to surfaces, followed by irreversible attachment, EPS formation, and maturation into complex structures.
    • Quorum Sensing: Mechanism allowing cells to communicate and coordinate behavior based on population density, affecting gene expression and biofilm stability.

  • Quorum Sensing and Health Implications

    • Biofilms in human health: can promote chronic infections, resist antibiotic treatment, and encapsulate high resistance traits.
    • Clinical infections examples include lung infections in cystic fibrosis and infections around medical devices.

  • Oxygen Requirements for Microbial Growth

    • Classifications: obligate aerobes, obligate anaerobes, facultative anaerobes, aerotolerant anaerobes, microaerophiles, and capnophiles.
    • Detoxification mechanisms involve enzymes like catalase and superoxide dismutase.

  • pH and Temperature

    • Microbial pH tolerance varies, with most bacteria thriving at neutral pH (around 7).
    • Temperature classifications include psychrophiles, mesophiles, thermophiles, and hyperthermophiles.

  • Culturing Methods

    • Different types of media: all-purpose, enriched, selective, differential, and defined media.
    • Objective of culturing: isolate specific organisms from mixed populations and study their characteristics.

  • Conclusion

    • Understanding the mechanisms of microbial growth and biofilm formation has wide applications in medicine, biotechnology, and ecology.
    • Continual research is vital to develop effective treatments against biofilm-associated infections and manage microbial behavior in various environments.