Bacterial growth curve:
When inoculated in a liquid nutrient medium, bacteria reproduce via
binary fission.
They follow a standard curve of 4 major phases
1. Lag phase:
a. Initial phase
b. Vigorous metabolic activity occurs
c. Nutrients are incorporated
d. Bacterial cells do NOT divide.
e. Lasts from minutes to hours.
2. Log (exponential) phase:
a. Rapid cell division occurs
b. Medically important period
c. β-lactam antibiotics are most effective in this phase
d. Work best when bacteria are synthesizing peptidoglycan to
divide.
3. Stationary phase:
a. Bacterial growth slows down as nutrients deplete and waste
products accumulate.
b. Number of new cells exactly balances dying cells
c. On a special apparatus, “chemostat” bacterial cells bypass the
stationary phase and remain in log phase. Chemostat
continuously provides nutrients and removes waste.
4. Death phase:
a. Final phase
b. Significant decline in number of viable bacteria
c. Essential nutrients are completely exhausted, causing most
cells to die.
Factors that affect bacterial growth:
Rate of growth is dependent on species of bacteria, temperature, pH,
amount of nutrients etc.
1. Oxygen availability:
a. Critical determinant of growth
i. Obligate aerobes:
1. Strictly require oxygen
2. ATP generating systems depend on it as a hydrogen
acceptor
When inoculated in a liquid nutrient medium, bacteria reproduce via
binary fission.
They follow a standard curve of 4 major phases
1. Lag phase:
a. Initial phase
b. Vigorous metabolic activity occurs
c. Nutrients are incorporated
d. Bacterial cells do NOT divide.
e. Lasts from minutes to hours.
2. Log (exponential) phase:
a. Rapid cell division occurs
b. Medically important period
c. β-lactam antibiotics are most effective in this phase
d. Work best when bacteria are synthesizing peptidoglycan to
divide.
3. Stationary phase:
a. Bacterial growth slows down as nutrients deplete and waste
products accumulate.
b. Number of new cells exactly balances dying cells
c. On a special apparatus, “chemostat” bacterial cells bypass the
stationary phase and remain in log phase. Chemostat
continuously provides nutrients and removes waste.
4. Death phase:
a. Final phase
b. Significant decline in number of viable bacteria
c. Essential nutrients are completely exhausted, causing most
cells to die.
Factors that affect bacterial growth:
Rate of growth is dependent on species of bacteria, temperature, pH,
amount of nutrients etc.
1. Oxygen availability:
a. Critical determinant of growth
i. Obligate aerobes:
1. Strictly require oxygen
2. ATP generating systems depend on it as a hydrogen
acceptor
