(LE2) Microbial Growth and Control

Question 1

What physical requirements are needed to be optimal for bacterial growth?

Answer 1

1. temperature
2. pH
3. osmotic pressure

Question 2

What are mesophiles? Give an example

Answer 2

Bacteria with optimal growth temperature of 37 degrees Celsius (human body temperature)
- pathogens
- Escherichia

Question 3

What are psychrophiles? Give an example

Answer 3

Bacteria with very cold optimum temperatures. Thrive in fridge
Flavobacterium

Question 4

What are thermophiles? Give an example

Answer 4

Bacteria with a very hot optimal growth temperature. Thrive near thermal vents
Thermus, Thermococcus

Question 5

What are acidophiles? Give an example

Answer 5

bacteria that prefer low pH
e.g. Helicobacter pylori (cause ulcers)

Question 6

How do we prevent drops in pH when culturing bacteria?

Answer 6

Adding buffers

Question 7

What byproduct is produced when bacteria eat sugars? Proteins?

Answer 7

Sugar = acid byproduct
Proteins = base byproduct

Question 8

Why are salt and sugar used as food preservatives?

Answer 8

Cause solute concentration around bacteria to be hypertonic, which causes plasmolysis

Question 9

What are halophiles? Give an example

Answer 9

Bacteria that prefer higher than normal salt concentration
e.g. Staphylococcus aureus (common cause of food poisoning)

Question 10

What common nutritional requirements do all cells have? Why?

Answer 10

All needed for cellular energy and building organic molecules
- carbon
nitrogen (proteins and nucleic acids)
phosphorus (nucleic acids and lipids)
sulfur (proteins)

• trace elements (mostly enzyme co-factors)
• vitamins and other organic growth factors (co-enzymes)

Question 11

What is normally formulated in nutrient agar and for what purpose?

Answer 11

Extracts and digests (beef protein)
- general growth

Question 12

What is normally formulated in enriched media and for what purpose?

Answer 12

extra ingredients like blood in BAP, for certain growth requirements

Question 13

What is chemically defined media? Give an example

Answer 13

Growth media formulated with specific ingredients to grow specific organisms
- e.g. citrate agar

Question 14

What growth media is used to measure microbial oxygen requirements?

Answer 14

Thioglycollate broth: O2 concentration gradient. Present at top, absent on bottom

Question 15

What enzymes are required for protection against oxidative damage?

Answer 15

Superoxide dismutase and catalase

Question 16

What are obligate aerobes? What is their appearance in Thioglycollate broth? What enzymes do they have against oxidative damage?

Answer 16

• Use aerobic respiration only
• contain both Superoxide dismutase and catalase

Question 17

What are facultative anaerobes? What is their appearance in Thioglycollate broth? What enzymes do they have against oxidative damage? Provide an example.

Answer 17

• use aerobic respiration if O2 available and anaerobic pathways if not
• contain both Superoxide dismutase and catalase
• majority of bacteria

Question 18

What are aerotolerant anaerobes? What is their appearance in Thioglycollate broth? What enzymes do they have against oxidative damage?

Answer 18

• do not use O2 but can survive if present
• contains only Superoxide dismutase

Question 19

What are microaerophiles? How do they appear in Thioglycollate broth? What enzymes do they have against oxidative damage? Provide an example.

Answer 19

• use aerobic respiration, but require low O2 concentration, ~ 1%
• contains both Superoxide dismutase and catalase at low concentration
• Neisseria gonorrhoeae

Question 20

What are obligate anaerobes? What is their appearance in Thioglycollate broth? What enzymes do they have against oxidative damage? Provide an example.

Answer 20

• do not use aerobic respiration. O2 is toxic
• contains no enzyme against oxidative stress
• Clostridium difficil

Question 21

What waste is produced after aerobic respiration? What does it do?

Answer 21

superoxide (O2-) - highly reactive, damages DNA, proteins, etc.

Question 22

How do SOD and catalase work against superoxides?

Answer 22

• SOD neutralizes O2- with H2O to make H2O2 (hydrogen peroxide)
• Catalase neutralizes H2O2 into water and oxygen

Question 23

What stage of the bacterial growth curve is indicated in the picture? What occurs in that phase?

Answer 23

Lag Phase
- acclimation to new environment

Question 24

What stage of the bacterial growth curve is indicated in the picture? What occurs in that phase?

Answer 24

Log Phase
- Max rate of exponential growth
- birth rate > death rate

Question 25

What stage of the bacterial growth curve is indicated in the picture? What occurs in that phase?

Answer 25

Stationary Phase - Running out of food - birth rate = death rate

Question 26

What stage of the bacterial growth curve is indicated in the picture? What occurs in that phase?

Answer 26

Decline/death phase - death rate > birth rate

Question 27

At what phase in the growth curve will bacteria begin to produce endospores?

Answer 27

Stationary phase

Question 28

What is sterilization?

Answer 28

killing or removal of all microorganisms on a material or object

Question 29

What is disinfection? What two agents are used for disinfection?

Answer 29

- reduction of the number of pathogenic microorganisms to the point they pose no danger of disease - antiseptics and disinfectants

Question 30

What are antiseptics?

Answer 30

chemical agent that can be safely used on living tissue to destroy or inhibit growth of microorganisms

Question 31

What are disinfectants?

Answer 31

Chemical agent used on inanimate objects to destroy microorganisms. Don't kill spores

Question 32

What is a bacteriostatic agent?

Answer 32

Chemical agent that inhibits the growth of bacteria

Question 33

What is a bacteriacide?

Answer 33

An agent that kills bacteria. Most do not kill spores

Question 34

How does growth rate influence microbial control?

Answer 34

faster growth rate = easier to kill slower growth rate = harder to kill

Question 35

How does temperature influence microbial control?

Answer 35

chemical agents work slower at colder temperatures

Question 36

How does the type/number of microbes affect microbial control?

Answer 36

some microbes are more difficult to kill

Question 37

How does the environment influence microbial control?

Answer 37

some chemical agents are deactivated by the presence of other organic compounds (i.e. blood, pus, feces, etc.)

Question 38

Describe the different methods of heating used to control growth

Answer 38

Dry heat: effective, but slow (incineration, oven) Moist heat: - Boiling: doesn't kill spores - autoclave: superheated steam (121*C) under pressure (15 PSI) = sterilization Soft heat: pasteurization: not sterile ; leaves some microbes

Question 39

Why would we use filtration as a method of control? What are the different pore sizes?

Answer 39

Used for heat-labile substances (vaccines and medication) - 0.45 microns: bacteria - 0.05 microns: viruses

Question 40

What methods of control do we use with low temperature and drying?

Answer 40

Refrigeration: bacteriostatic Desiccation: spores survive Lyophilization: freeze-drying

Question 41

How is osmotic pressure a method of control?

Answer 41

causes plasmolysis

Question 42

How is radiation a method of control? What are the types of radiation?

Answer 42

Damages DNA and proteins Ionizing: penetrating (e.g. x-rays and gamma rays) Non-ionizing: good for surfaces (e.g. UV light)

Question 43

How do soaps and detergents work? Give an example

Answer 43

They are surfactants (like phospholipids), damages cell membranes - quaternary ammonium compounds (mopping solutions) for surfaces

Question 44

How do phenol and it's derivatives work? Give an example

Answer 44

Damage membranes and denature proteins - not inhibited by organic materials e.g. Lysol or Cholorohexidine

Question 45

How do alcohols work? Give an example

Answer 45

Highly effective in damaging membranes and denature proteins - safe for skin - evaporates quickly e.g. hand sanitizer

Question 46

How do organic acids work? Give an example

Answer 46

Bacteriostatic by slowing /preventing fermentation e.g. food preservatives

Question 47

How do halogens work? Give an example

Answer 47

Damages proteins e.g. Chlorine and Iodine (antiseptic)

Question 47

How do heavy metals work? Give an example

Answer 47

Damages proteins - silver nitrate: newborn eyedrops - organic mercury: antisepsis

Question 47

How do oxidizing agents work? Give an example

Answer 47

Denature proteins e.g. peroxide (antiseptic)