UTA Microbiology Exam 3 All Answers Correct
Microbial Growth and Reproduction
#### 4 Basic Steps of Binary Fission
1. Growth of cell size
2. Replication of DNA
3. Division of cytoplasm
4. Septum formation & cell division
#### Z Ring Assembly - FtsZ: Assembles Z ring to form a divisom...
- FtsZ: Assembles Z ring to form a divisome (cell division apparatus).
#### Generation Time
- The time it takes for a microbial population to double.
### Growth Phases of Bacteria
1. Lag Phase:
- Cells adjust to culture medium; no change in population.
- Duration is affected by:
- Genetic makeup
- Media composition
- Initial inoculum size
2. Log Phase:
- Characterized by binary fission; cell replication rate exceeds cell death rate.
- Most appropriate phase for antibiotic use.
3. Stationary Phase:
, - Resources become depleted; cell respiration = cell death.
4. Death Phase:
- Endospores may form; cell replication rate is less than cell death rate.
5. Persisters:
- Surviving cells considered important in chronic infections (e.g., Tuberculosis).
### Culture Types
- Closed System Cultures: Have finite resources.
- Open System Cultures:
- Nutrients and air are replenished.
- Dead cells and waste are removed.
- Beneficial for industrial microbiology.
### Cell Counting Methods
- Microscopic Cell Count:
- Cells are counted under a microscope using a laser-etched slide.
- Inability to distinguish between live vs. dead cells is a limitation.
- Fluorescence Staining:
- Cell counting performed under a microscope or flow cytometer.
- Live cells stain Green; Dead cells stain Red.
- Coulter Counting:
- Detects electrical resistance change due to cell density.
- Viable Cell Counts:
- Samples are diluted and grown on solid media.
, - Counts only living cells.
- Countable range: 30-300 CFU/ml.
- Optical Density:
- Measured with a spectrophotometer; provides an indirect approach to measuring growth as it
measures light passed through a culture.
### Cell Counting Techniques
1. Pour Plate Technique:
- Sample mixed with warm agar (45-50°C), poured onto sterile plates, and swirled to mix.
2. Spread Plate Technique:
- Sample poured onto solid medium and spread using an L spreader.
3. Membrane Filtration:
- Used for counting colonies from drinking water.
4. Most Probable Number (MPN):
- Method used in food/water testing, particularly when counts are lower than 30 CFU/ml.
### Biofilm Formation Steps
1. Attachment of planktonic cells.
2. Cells become sessile.
3. Growth & Division on substrate.
4. Production of extracellular polymeric substances (EPS).
5. Attachment of secondary colonizers and dispersion.
#### Quorum Sensing
- Definition: Cell-to-cell communication regarding cell density.
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