UNIT 3 Flashcards
• Orderly increase in the sum of all the
components of an organism
• cell multiplication, increase in the
number of single bacteria making up
population , “culture”.
Growth
• Measure of cell concentration
The measurement of Microbial
concentration
• Can be measured by cell
concentration (the number of
viable cells per unit volume of
culture)
• biomass concentration (dry
weight of cells per unit volume
of culture)
Viable cell count
_________
• Measured by photoelectric means
• Related to viable count using a
________
• a barely turbid suspension of Escherichia coli contains about 107 cells per
milliliter, and a fairly turbid suspension contains about 108 cells per milliliter.
Turbidity
standard curve
• The Growth Rate Constant
• Can be measured in grams of
biomass produced per hour
Exponential growth
Physical Requirements for Growth:
Temperature
• Minimum growth temperature
• Optimum growth temperature
• Maximum growth temperature
Five groups based on optimum growth temperature
- Psychrophiles
- Psychrotrophs
- Mesophiles
- Thermophiles
- Hyperthermophiles
period of little or no cell division and it can last for 1 hour or several days
LAG
cells begin to divide and enter a period of growth or logarithmic
increase; cells are most active metabolically
LOG
metabolic activities of individual surviving cells slow; microbial death balance the no. of new cells; period of equilibrium
Stationary
no. of death exceeds the no. of new cells formed
Death
Definition and Measurement of Death
▪ death mean irreversible loss
▪ if it fails to give rise to a colony
▪ depends on the medium
▪ first hour after treatment are also critical in the determination of “killing.”
▪ how to control the growth of bacteria?
▪ immune system and nutrient limitation
▪ physical methods:
__________
__________
__________
__________
▪ sterilization
▪Disinfection
▪Pasteurization
▪ aseptic technique
