Microbiology Lecture 5

Question 1

Do bacterial growth curves exhibit symmetry? What are they like?

Answer 1

Not symmetrical, they can tolerate temperatures below their optimal, but will quickly die above.

Question 2

What is the optimum temperature for mesophiles?

Answer 2

37C

Question 3

What 3 factors limit bacterial growth when temperatures are lower than the optimum?

Answer 3

• Cell membrane loses fluidity
• Enzymes stop working
• Transport slows down

Question 4

What 3 factors limit bacterial growth when temperatures are higher than the optimum?

Answer 4

• Protein denaturation
• rRNA denaturation
• Cell membrane becomes too fluid

Question 5

Do cycles of freezing and thawing encourage or inhibit bacterial growth, and why?

Answer 5

Inhibits, as the ice crystals poke holes in the cells of the bacteria’s host, releasing nutrients and encouraging growth.

Question 6

Are pH growth curves symmetrical? What is the typical tolerance range for bacteria?

Answer 6

Yes, they tend to be.

Most grow between 6.5-7.5

Question 7

When bacterial cultures grow, does pH tend to increase, or decrease? Why is this so? What effect does this have? What can be done to avoid this when culturing them?

Answer 7

They tend to release acids, resulting in decreasing pH. These acids interfere with their growth.
Buffers can be used to minimise this.

Question 8

True or false

Yeast and fungi do not tolerate low pH well.

Answer 8

False

Question 9

Do mycoplasma have a true cell wall?

Answer 9

No.

Question 10

Define moderate halophile.

Answer 10

Only grows when a minimum amount of salt exists, cannot grow in its complete absence.

Question 11

Define halotolerant.

Answer 11

Do not require salt to grow, but can tolerate a certain range only.

Question 12

Define aW.

Answer 12

Amount of water free to react.

Question 13

Which organism grows well at low aW?

Answer 13

Fungi.

Question 14

Define aerobe.

Answer 14

Requires oxygen for growth.

Question 15

Define anaerobe.

Answer 15

Grows only in the absence of oxygen.

Question 16

Facultative anaerobe.

Answer 16

Will grow with or without oxygen.

Question 17

Which bacteria is responsible for allowing anaerobes to live in the bowel? How does this work out?

Answer 17

E. coli. Is a facultative anaerobe that will use up all the oxygen in the bowels, depriving it entirely.
This allows anaerobes to grow.
E. coli is a facultative anaerobe, and will continue to grow regardless.

Question 18

Define strict/obligate aerobe.

Answer 18

Strictly requires oxygen for growth, used in oxidative metabolism.

Question 19

Name the shape and gram status of pseudomonas, and its oxygen requirements.

Answer 19

Strict aerobe

Gram negative rod

Question 20

What kind of environment do strict anaerobes require?

Answer 20

Reducing environment.

Question 21

Do strict anaerobes die on exposure to air?

Answer 21

Yes.

Question 22

Can strict anaerobes tolerate oxygen exposure?

Answer 22

Yes, but only some.

Question 23

How do strict anaerobes derive energy?

Answer 23

Fermentative metabolism.

Question 24

Do strict anaerobes have an electron transport pathway?

Answer 24

No.

Question 25

Define aerotolerant anaerobe.

Answer 25

Grows the same in O2 as it does in anO2

Question 26

Do facultative anaerobes grow better with or without oxygen?

Answer 26

With.

Question 27

Define capnophilic.

Answer 27

Prefers the presence of 10% CO2

Question 28

Define microaerophilic.

Answer 28

Requires less oxygen than atmosphereic O2, but not 0%.

Question 29

Define the lag phase, and what occurs during this phase.

Answer 29

Bacterial numbers are constant. Bacteria are preparing for growth by making the required proteins for growth and nutrient uptake.

Question 30

Define the exponential growth phase, and what occurs during this phase.

Answer 30

Cell numbers double at a constant rate.

Question 31

Define the stationary phase, and what occurs during this phase.

Answer 31

If nutrients are limited, growth cannot continue indefinitely. Net number remains constant.

Question 32

Define the death phase, and what occurs during this phase.

Answer 32

No cell growth, cells begin to die and may lyse.

Question 33

Describe the morphology, gram status, and oxygen requirements of campylobacter.

Answer 33

Gram negative curved rod. | Capnophilic.

Question 34

Describe the morphology, gram status, and oxygen requirements of E. coli.

Answer 34

Gram negative rod. | Facultative anaerobe.

Question 35

Describe the morphology, gram status, and oxygen requirements of lactobacillus.

Answer 35

Gram positive rod. | Aerotolerant anaerobe.

Question 36

Describe the morphology, gram status, and oxygen requirements of clostridium.

Answer 36

Gram positive rod. | Strict anaerobe.

Question 37

What 4 symptoms are caused by clostridium?

Answer 37

Gas gangrene Botulism Tetanus Hospital acquired diarrhoea

Question 38

Describe the morphology, gram status, and oxygen requirements of pseudomonas.

Answer 38

Gram negative rod. | Strict anaerobe.