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Microbial Growth (Enviromental Factor (Temperature …
Microbial Growth
Enviromental Factor
Temperature
- Minimum growth temperature
- Optimum growth temperature
- Maximum growth temperature
- Psychrophile : 15-20 *c
- Mesophile : 25-40 *c
- Thermophiles : 50-60 *c
pH
- Acidophiles (optimum pH 0.1-5.5)
- Neutrophiles (optimum pH 5.5-7)
- Alkalophiles (optimum pH 8.5-11.5)
Oxygen
- Obligate
- organism needs strictly specific enviromental condition
- Facultative
- organism is able to adjust and tolarate to enviromental conditon
- Aerobes
- Obligate aerobes
- must have free oxygen for aerobic respiration (Pseudomonas sp.)
- Anaerobes
- do not require oxygen to grow
- Obligate anaerobes
- kill by the free oxygen (Bacteroides sp.)
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Phases of Growth
Log phase (exponential)
- Logarithmic (log) phase
- Highest metabolic activity (active)
- Most rapid growth
- Population double every generation
- No cell produced > no cell dying
Stationary phase
- No cell produced = no cell dying
- Cell division slow down
- Total no of viable cell constant
- Limited nutrient, oxygen
- Metabolic waste accumulates
- Critical population density
Lag phase
- Little or no cell division
- Adapt/adjust to new condition
- Metabolically active - grow in size, synthesize enzyme and incorporate molecules from medium
- Produce large quantities of energy in the form of ATP
Death phase
- Decline phase
- No cell produced < no cell dying
- Metablic waste accumulates and becomes toxic to cell
- Cell lose their ability to devide and thus die
Measurement of Growth
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Membrane Filtration
- Measure viable cells only
- Useful in analzing water purity
- Measure total coliform count
Standard Plate Count
- Dilution of original bacterial culture with known volume
- Transfer each dilution onto agar plate (spread/pour plate)
- Measure viable cell only
Direct Microscopic Count
Petroff-Hausser countin chamber (hemocytometer)
- Bacterial suspension introduced onto chamber with calibrated pipette
- Microorganisms counted in specific calibrated areas
- No per unit volume is calculated using appropriate formula
- Measure viable and non-viable cells
Electronic counter
- e.g. Coulter counter
- Count large microorganism (protozoa, yeast)
- Use current flow
- Measure viable and non-viable cells
Microbial Growth
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Microb grow and devided
- Binary fission (Bacillus)
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