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Microbial control Flashcards

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1
Q

How is microbial growth effected?

A

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

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2
Q

What does microbial growth involve the use of?

A

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

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3
Q

What are the principles of microbial control?

A
  • Prevention → Control of growth to prevent infection
  • Sterilization → Complete destruction
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4
Q

What are the levels of sterilization?

A
  • No ‘levels’ of sterilization → All or Nothing
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5
Q

What does sterilization utilize?

A
  • Utilizes
    a. Heat
    b. Radiation
    c. Some chemicals
    d. Physical removal
    (e. Other organisms)
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6
Q

What are the Principles of Microbial Control 2 ?

A
  • Disinfection → reducing growth on non living surfaces
    - (Organic matter interferes with heat treatments and chemical control agents)
  • Antisepsis → reducing growth on living tissue
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7
Q

What are the physical methods of controling microbial growth?

A

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

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8
Q

What physical method is most commonly used?

A

Heat

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9
Q

What are the variables of heat?

A
  1. Type of heat
  2. Time of Application
  3. Temperature
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10
Q

How is moist and heat used on microbes?

A

Boiling/autoclaves

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11
Q

How does heat kill microbes?

A

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

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12
Q

To what temperature do bacteria need to be heated?

A
  • 121o C for 30 minutes kills nearly all microbes
  • Prions may not be destroyed at the typical 134 °C for 3 min (hospital method)
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13
Q

What is the thermal death point?

A

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

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14
Q

What is TDP?

A

thermal death point

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15
Q

What is thermal death time?

A
  • time span required to kill all the bacteria in a broth at a given temperature
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16
Q

What is TDT?

A

Thermal death time

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17
Q

What is decimal reduction time?

A

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

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18
Q

WHat is DRT?

A

Decimal reduction time

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19
Q

How does an autoclave work?

A

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

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20
Q

What happens to heat-labile substances in an autoclave?

A

Heat-labile substances
will be denatured

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21
Q

Why is time vs pressure important?

A

pressure dictates the boiling temperature.

The higher the pressure, the higher the boiling temperature.

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22
Q

What is Dry Heat Sterilization also known as?

Study These Flashcards
A

Direct flaming

23
Q

What are the typical temps of a bunsen burner flame?

Study These Flashcards
A

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

24
Q

What flame is air hole closed?

25
What flame is air hole fully open?
roaring blue flame
26
What are the different methods of dry heat Sterilization?
Bunsen burner - direct flaming Incineration
27
How is incineration carried out?
Hot-air sterilization (in an Oven)
28
Describe Pasteurization.
- heating at high temperature for a short time - Batch method 63°C for 30 min - Flash method 72°C for 15 s
29
What product is always pasteurized?
Milk
30
How is milk pasteurized?
Ultra-High-Temperature (UHT) 140 °C for 3 seconds
31
What are the effects of pasteurized milk?
→Long shelf life →Taste change →Some nutritional loss can occur in UHT milk →(folate, some B vitamins, vitamin C)
32
What is filtration?
- The passage of a liquid or gas through a filter with pores small enough to retain microbes
33
Why is Filtration important?
important to sterilize solutions which would be denatured by heat (antibiotics, injectable drugs, amino acids, vitamins)
34
What does a decreasing temperature do for chemical acitivty?
Decreasing temperature decreases chemical activity. This means metabolism slows Thus growth slows.
35
Are low temperatures bactericidal or bacteriostatic?
bacteriostatic
36
Define bacteriostatic
“bacteriostatic” means that the agent/drug prevents the growth of bacteria; it keeps them in the stationary phase of growth.
37
Define bactericidal.
“bactericidal” means that the agent/drug kills bacteria/an antibiotic that kills bacteria.
38
What is antibiotic resistance?
Antibiotic resistance is when bacteria become resistant to the drugs which are supposed to kill them.
39
40
Does water frozen quickly kill bacteria?
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
41
Does water frozen slowly kill bacteria?
- 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
42
What is freezing food used to do?
 Used to slow down food deterioration
43
What temp is food usually frozen at?
Usually done at -18oC. Lower than -30oC is usually too expensive
44
How does freezing food help disrupt bacteria cells?
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”
45
How does desiccation and dehydration stop growth of bacteria?
 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
46
How is drying by osmotic pressure done?
Salting/curing foot or covering food with sugar. ----May still get some mould or yeast growth
47
How does curing meat stop microbial growth?
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
48
How does radiation kill bacteria?
- Destroys or damages DNA - Dependent on the wavelength, intensity, and duration. EG GAMMA RAYS AND RADIO WAVES
49
When are gamma rays used?
Commonly used for sterilization of disposable medical equipment (syringes, needles, cannulas)
50
When is radiotherapy used?
ionizing radiation to kill malignant cells
51
How does food irradiation work?
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
52
How are microwaves used to kill bacteria?
Kill microbes indirectly with heat (microwave radiation heats water and other polarized molecules in the food)
53
Give some examples of chemical methods used to control microbial growth.
- Antibiotics - Antibacterial drugs - Antiviral - Antifungal
54
What is an Antibiogram?
➢ 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

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