Chapter 6: Microbial Growth

Question 1

Factors that Determine Microbial Growth

Answer 1

1. Temperature
   a. Psychrophiles
   b. Mesophiles
   c. Thermophiles
2. pH
3. Osmotic Pressure
4. Oxygen
   a. Obligate Aerobes
   b. Obligate Anaerobes
   c. Facultative Anaerobes
   d. Aerotolerant Anaerobes
   e. Microaerophiles

Question 2

Psychrophiles

Answer 2

Temperature: Cold-loving

1. True:
   a. Can grow 0c
   b. Optimum growth 15c
   c. Can’t grow 20-25c
2. Facultative (psychrotrophs)
   a. Can grow 0c
   b. Optimum 25c
   c. Cannot grow ~40c
   - causes diseases (food spoilage)

Question 3

Mesophiles

Answer 3

Temperature: Middle

a. Can grow: 25-40c
b. Optimum: 37c
c. Cannot grow: ~50c

Question 4

Thermophiles

Answer 4

Temperature: Prefers hot
a. Can't grow below 45c
b. Optimum is 50-60c
c. Can grow 80-130c
no health concerns

Question 5

pH

Answer 5

• Most bacteria can grow between 6.5-7.5

- Molds and yeasts grow b/w 5-6

Question 6

Osmotic Pressure

Answer 6

Isotonic, hypertonic, hypotonic

- Prefers Isotonic

Question 7

Obligate Aerobes

Answer 7

1. Needs O2 to grow
2. Produces 38 ATP
3. Final electron acceptor is oxygen
4. Most bacteria belong to this group

Question 8

Obligate Anaerobes

Answer 8

1. Can’t use O2
2. Produces variable ATP (only does glycolysis and part of krebs_)
3. Harmed by O2
4. The final electron acceptor is an inorganic molecule eg. Clostridium bacteria (Clostridium tetani)

Question 9

Facultative Anaerobes

Answer 9

1. When O2 is available, they prefer it (increased growth) can produce 38 ATP in aerobic mode
2. When O2 is unavailable, they still function (variable ATP in anaerobic mode)
3. Could go into fermentation if necessary
4. Final electron acceptor can be O2 or any other
   eg. Escherichia coli

Question 10

Aerotolerant Anaerobes

Answer 10

1. Tolerate oxygen
2. Choose not to use O2 for energy-yielding purposes
3. Obligate fermenters
4. Lactobacillus species, yeast

Question 11

Microaerophiles

Answer 11

1. Use O2, but in micro quantities (are anaerobes). 2-10% of atmospheric O2.
2. Helicobacter pylori (grows in stomach and causes peptic ulcers), Campylobacter jejuni (grows in intestine and causes gastroenteritis)

Question 12

Toxic Oxygen

Answer 12

1. Singlet oxygen: O2 boosted to a higher energy state
2. Superoxide Radical O2.
   a. Steals an electron –> cell death
   b. 2 O2 + 2 O2 + 2H+ –> H2O2 + O2
   - Superoxide Diomotase
3. Peroxide Anion
   a. H2O2 –> O2^2-
   - Enzyme Catalase: H2O2 –> H2O + O2
   - Peroxide H2O2 –> 2H2O
   
   • Peroxide will steal electrons and become hyperoxide radical if it is not neutralized.

Question 13

Culture Medivuis

Answer 13

1. Nutrient proton after a while cultures will grow
2. Nutrient Agar
   - used as a solidifying agent
   - can be melted and resolution
   - Solid at 37 degrees
   - Can’t be “taken away” by organs

Question 14

Selective Media

Answer 14

Biomath sulphite Agar
- To grow Salmonella typhi
Causes: typhoid fever

Question 15

Differential Media

Answer 15

Blood Agar
- To grow Streptococcus pyogenic
Causes: strep throat

Question 16

Selective and Differential Media

Answer 16

Monnital Salt Agar
- To grow: Staphylococcus aureus
Causes: Toxic Shock Syndrome

Question 17

Bacteria Phase Growth

Answer 17

1. Lag Phase: Intense activity preparing for population growth but no increase in population
2. Log Phase: generation time logarithmic or exponential increase in population
   - Due to binary fission in bacteria, or mitosis in yeast
   - 60 mins x hours / # of generations = Gen time
   2^0 - 2^1 - 2^2 (subscript is generation number)
   Every cell divides into two
   - Log phase is the most susceptible phase to antibiotics
3. Stationary Phase: Period of equilibrium; microbial deaths balance the production of new cells.
4. Death Phase: population is decreasing at a logarithmic rate