Biofilm Formation and Structure

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.

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.