PowerPoint 5 - Microbial Growth

Definition: Microbial growth refers to the increase in the number of bacterial cells, not the size of individual microorganisms.
Colony Formation:
- Starts from a single mother cell.
- Cell division occurs via binary fission, creating offspring that form visible colonies in favorable conditions.

Mechanism of Cell Division:
- Common in bacteria, binary fission is a form of asexual reproduction.
- The cell grows and duplicates its cellular components before dividing.
DNA Replication:
- Begins at the origin of replication on the circular chromosome, attached to the inner cell membrane.
- Continues until reaching the terminus, leading to the formation of new daughter cells through cytokinesis.
Visual Representation:
- Electron micrographs depict the process and stages of binary fission in bacteria like Salmonella typhimurium.

Role of FtsZ Protein:
- A key protein (similar to tubulin in eukaryotic cells) directs cytokinesis.
- It assembles a Z ring on the cytoplasmic membrane, defining the division plane between daughter cells.
Divisome Formation:
- Additional proteins join the Z ring to form the divisome, initiating new cell wall synthesis and septum formation.

Definition: Time for a bacterial population to double through one round of binary fission.
Escherichia coli: Optimal doubling time of about 20 minutes, which may extend to several days under harsh conditions.
Generation Figures:
- A single cell increases to over 1 million in 20 generations (~7 hours).
- Example: Mycobacterium leprae doubling time is 14 days.

Growth Curve Phases:
- Lag Phase: Initial phase, characterized by cell adjustment and preparation for division.
- Log Phase: Rapid exponential growth and division; cells are most metabolically active and susceptible to antibiotics.
- Stationary Phase: Balance between cell division and death, reaching carrying capacity.
- Death Phase: Increased waste and nutrient depletion lead to cell death; persister cells may survive.

Methods:
- Plate Count: Viable cells counted based on visible colonies, expressed in CFUs.
- Serial Dilution: Helps achieve manageable counts within accurate statistical ranges for microbial estimates.
- Filtration Method: Used for low bacterial counts in samples like water to detect coliforms.
- Coulter Counter: Counts cells as they pass through a detector in a liquid sample.

Characteristics:
- Structured microbial communities that thrive on surfaces, secreting extracellular polymeric substances (EPS) to form a protective matrix.
Quorum Sensing:
- Communication between cells in biofilms using signaling molecules to coordinate responses based on population density.
Clinical Relevance:
- Biofilms can enhance resistance to antibiotics and contribute to chronic infections.

Anaerobic Environments: Locations like bogs or the rumen provide oxygen-free conditions favorable for specific bacteria.
pH and Temperature Tolerance:
- Microbes have specific ranges required for optimal growth (e.g. neutrophiles near pH 7, thermophiles thrive at high temperatures).
Salt Concentration: Halophiles adapt to high salinity environments, such as those found in salt lakes.

Types of Media:
- Agar: The most common solidifying agent, solidifies at temperatures below 40°C.
- Selective and Differential Media: Used to isolate specific microbes or distinguish between different species based on color change.
Examples:
- MacConkey agar differentiates lactose fermenters (e.g., E. coli) from non-fermenters.
- Blood agar identifies hemolytic bacteria like Listeria.