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.