Microbial control

Question 1

How is microbial growth effected?

Answer 1

Effected in two basic ways:
1. Killing microorganisms
2. Inhibiting microbial growth

Question 2

What does microbial growth involve the use of?

Answer 2

Involves the use of:
1. Physical agents that kill or prevent growth
2. Chemical agents that kill or prevent growth

Question 3

What are the principles of microbial control?

Answer 3

• Prevention → Control of growth to prevent infection
• Sterilization → Complete destruction

Question 4

What are the levels of sterilization?

Answer 4

• No ‘levels’ of sterilization → All or Nothing

Question 5

What does sterilization utilize?

Answer 5

• Utilizes
  a. Heat
  b. Radiation
  c. Some chemicals
  d. Physical removal
  (e. Other organisms)

Question 6

What are the Principles of Microbial Control 2 ?

Answer 6

• Disinfection → reducing growth on non living surfaces
  - (Organic matter interferes with heat treatments and chemical control agents)
• Antisepsis → reducing growth on living tissue

Question 7

What are the physical methods of controling microbial growth?

Answer 7

Heat
Filtration
Low temperatures
Desiccation
Osmotic pressure
Radiation

Question 8

What physical method is most commonly used?

Answer 8

Heat

Question 9

What are the variables of heat?

Answer 9

1. Type of heat
2. Time of Application
3. Temperature

Question 10

How is moist and heat used on microbes?

Answer 10

Boiling/autoclaves

Question 11

How does heat kill microbes?

Answer 11

denatures enzymes - kills most vegetative cells
and inactivates viruses within 10 min

Question 12

To what temperature do bacteria need to be heated?

Answer 12

• 121o C for 30 minutes kills nearly all microbes
• Prions may not be destroyed at the typical 134 °C for 3 min (hospital method)

Question 13

What is the thermal death point?

Answer 13

lowest temperature to kill all the bacteria in a broth in 10 Minutes

Question 14

What is TDP?

Answer 14

thermal death point

Question 15

What is thermal death time?

Answer 15

• time span required to kill all the bacteria in a broth at a given temperature

Question 16

What is TDT?

Answer 16

Thermal death time

Question 17

What is decimal reduction time?

Answer 17

length of time in which 90% of a bacterial population will be killed at a given temperature

Question 18

WHat is DRT?

Answer 18

Decimal reduction time

Question 19

How does an autoclave work?

Answer 19

Steam under pressure.
121 degrees c for 30 min at 15 lb/in^2
Steam must contact material in order to work.

Question 20

What happens to heat-labile substances in an autoclave?

Answer 20

Heat-labile substances
will be denatured

Question 21

Why is time vs pressure important?

Answer 21

pressure dictates the boiling temperature.

The higher the pressure, the higher the boiling temperature.

Question 22

What is Dry Heat Sterilization also known as?

Answer 22

Direct flaming

Question 23

What are the typical temps of a bunsen burner flame?

Answer 23

Typical temperatures of Bunsen burner flame: 1,300 to 1,600 °C)

Question 24

What flame is air hole closed?

Answer 24

Safety flame

Question 25

What flame is air hole fully open?

Answer 25

roaring blue flame

Question 26

What are the different methods of dry heat Sterilization?

Answer 26

Bunsen burner - direct flaming
Incineration

Question 27

How is incineration carried out?

Answer 27

Hot-air sterilization (in an Oven)

Question 28

Describe Pasteurization.

Answer 28

• heating at high temperature for a short time
• Batch method 63°C for 30 min
• Flash method 72°C for 15 s

Question 29

What product is always pasteurized?

Answer 29

Milk

Question 30

How is milk pasteurized?

Answer 30

Ultra-High-Temperature (UHT) 140 °C
for 3 seconds

Question 31

What are the effects of pasteurized milk?

Answer 31

→Long shelf life
→Taste change
→Some nutritional loss can occur in
UHT milk
→(folate, some B vitamins, vitamin C)

Question 32

What is filtration?

Answer 32

• The passage of a liquid or gas through a filter with pores
  small enough to retain microbes

Question 33

Why is Filtration important?

Answer 33

important to sterilize solutions which would be
denatured by heat (antibiotics, injectable drugs, amino acids, vitamins)

Question 34

What does a decreasing temperature do for chemical acitivty?

Answer 34

Decreasing temperature decreases chemical activity.
This means metabolism slows
Thus growth slows.

Question 35

Are low temperatures bactericidal or bacteriostatic?

Answer 35

bacteriostatic

Question 36

Define bacteriostatic

Answer 36

“bacteriostatic” means that the agent/drug prevents the growth of bacteria; it keeps them in the stationary phase of growth.

Question 37

Define bactericidal.

Answer 37

“bactericidal” means that the agent/drug kills bacteria/an antibiotic that kills bacteria.

Question 38

What is antibiotic resistance?

Answer 38

Antibiotic resistance is when bacteria become resistant to the drugs which are supposed to kill them.

Question 40

Does water frozen quickly kill bacteria?

Answer 40

When you freeze water quickly the water modules bond in a
haphazard way
- The water crystals are small
- The ice is white
- And not very strong
- Bacteria can survive

Question 41

Does water frozen slowly kill bacteria?

Answer 41

• When water is frozen slowly the water molecules can move
  and form a large crystals
• The ice is clear
• It is stronger than concrete
• It can break open cells
• And thus, kill cells

Question 42

What is freezing food used to do?

Answer 42

 Used to slow down food
deterioration

Question 43

What temp is food usually frozen at?

Answer 43

Usually done at -18oC.

Lower than -30oC is usually
too expensive

Question 44

How does freezing food help disrupt bacteria cells?

Answer 44

Water molecules do not stop
moving until -140oC
 So, water rearranges itself from a small loose crystal over time
to a large had compact one in a freezer over time
 This not only disrupts bacterial cells, but the cells of the frozen
food
 The food is ‘mushy’ when defrosted
 This is why frozen foods have a “best before date”

Question 45

How does desiccation and dehydration stop growth of bacteria?

Answer 45

 Most metabolic reactions take place between molecules
dissolved in water
 The other medium is lipid
 Remove the water from a cell and metabolism slows or stops
 Growth thus slows or stops

Question 46

How is drying by osmotic pressure done?

Answer 46

Salting/curing foot or covering food with sugar.

—-May still get some mould or yeast growth

Question 47

How does curing meat stop microbial growth?

Answer 47

1. Meat rubbed with salt (sodium
   chloride or sodium nitrite)
2. The salt draws out the water
3. Water evaporates off
   dehydrating the meat
4. Water content too low for
   life to survive
5. Nitrite kills organisms by
   oxidation

Question 48

How does radiation kill bacteria?

Answer 48

• Destroys or damages DNA
• Dependent on the wavelength, intensity, and
  duration.
  EG GAMMA RAYS AND RADIO WAVES

Question 49

When are gamma rays used?

Answer 49

Commonly used for sterilization of disposable medical
equipment (syringes, needles, cannulas)

Question 50

When is radiotherapy used?

Answer 50

ionizing radiation to kill malignant cells

Question 51

How does food irradiation work?

Answer 51

Treating certain foods to a specific dosage of ionizing radiation
Damages the DNA & RNA of pathogens
Food does not accumulate radiation. Less effect on appearance and texture

Question 52

How are microwaves used to kill bacteria?

Answer 52

Kill microbes indirectly with heat (microwave radiation
heats water and other polarized molecules in the food)

Question 53

Give some examples of chemical methods used to control microbial growth.

Answer 53

• Antibiotics
• Antibacterial drugs
• Antiviral
• Antifungal

Question 54

What is an Antibiogram?

Answer 54

➢ Method of testing the efficacy of antibiotics to cultured bacteria
➢ Clear zone indicates bactericidal activity.
➢ The greater the diameter of the zone, the higher the efficacy of the antibiotic