Chapter 6: Microbial Growth Flashcards
Physical requirements for microbial growth
Temperature
pH
Osmotic pressure
Chemical requirements for microbial growth
CHONPS
Growth factors and trace elements
Physical requirements - Temperature
all species have a minimum (lowest), optimum (best), and maximum (highest) at which they will grow
M/O can be classified by their optimum temperatures
Psychrophile
“Cold loving”
2 groups of psychrophiles
- Can grow at 0°C, optimum growth is 15°C, will not grow above 25°C
- Can grow at 0°C, optimum growth is 20-30°C, won’t grow above 40°C
- responsible for most food spoilage -> psychrotroph
Mesophiles
”Moderate-temp-loving “
optimum growth temperature is 25-40°C (~37°C)
most common group, includes most pathogens!
Thermophiles
”heat loving”
optimum growth temp. is 50-60°C
Hyperthermophiles
”extreme thermophiles”
optimum growth temp. is 80°C, or higher
usually members of the archaea
Danger zone
15-53°C
➖rapid growth of bacteria; may produce toxins
Physical requirements - pH
most M/O grow near neutrality ~6.5-7.5
➖pH of blood ~7.38, ideal for most pathogens
few bacteria can grow below a pH~4
Acidophiles
“acid loving”
very small group
several foods are preserved by acids produced by formative bacteria
➖cheese, sauerkraut, pickles
Physical requirements - osmotic pressure
The pressure required to stop the flow of water across a selectively permeable membrane
Plasmolysis
Osmotic loss of water -> shrinkage of plasma membrane away from the cell wall
principle of food preservation using salt and sugars -> increase the osmotic pressure
Plasmoptysis
Osmotic gain of water = cell bursting
Chemical Requirements - Carbon
Structural “backbone” of all living matter
~50% of the cell is made up of carbon
Nitrogen (N) 14%
Sulfur (S)
Phosphorus (P)
N+S Required for protein synthesis
N+P Required for DNA, RNA, and ATP
N sources include proteins, ammonium ions (NH4+), nitrate ions (NO3-), nitrogen gas (N2)
S sources include sulfate ions (SO42-), hydrogen sulfide gas (H2S), amino acids (cysteine)
P sources include phosphate ions (PO43-)
Trace Elements
Other minerals such as Fe, Cu, Zn, Mg,
etc. act as cofactors for enzymes
Chemical Requirements - Oxygen
Aerobic respiration is more efficient than anaerobic
Any organism that can grow in the presence of
oxygen must have…
Superoxide dismutase (SOD) to neutralize harmful forms of oxygen radicals (O2->H2O2 hydrogen peroxide); and
Catalase H2O2 -> H2O + O2 orPeroxidaseH2O2 + 2H+ -> 2H2O
Culture medium
“Food”
Material used to grow M/O
Media must meet what 3 criteria?
Contain appropriate nutrients, proper pH, moisture
Must be sterile!
Must be incubated at the proper temperature for growth
Inoculum
Microbes introduced into the media
Culture
The inoculum that grows on the media
General time
The time required for a cell to divide (or a population to double)
Typically 1-3 hours but varies, could be 12 days
Under ideal conditions could be 20 minutes
Bacterial growth curve
Demonstrates the growth of cells over time
Bacterial growth is exponential
