Chapter 7: Control of Microbial Growth

Question 1

Physical Methods of Control

Answer 1

1. Heat
   a. Moist heat (boiling, autoclave, pasteurization)
   b. Dry Heat (inoculating loops, incineration, hot-air sterilization
2. Filtration
3. Radiation
   a. Ionizing
   b. Non-ionizing

Question 2

Chemical Methods

Answer 2

1. Phenol
2. Halogens
3. Alcohols Denature
4. Quats
5. Gas

Question 3

Moist Heat

Answer 3

Denaturation of Proteins

1. Boiling: hot removal of all microbial life; also leaves endospores.
2. Autoclave: steam under pressure. 121c/ 18 mins/ 15 psi.
   - eg, for surgical instruments, media/culture media. A small-scale example is a pressure cooker.
3. Pasteurization
   a. Classic/Baten - 63c / ~30 mins.
   b. High temp short time (flash) - 72c / 15 secs.
   c. Ultra-high temp: 140c for ~4 seconds

Question 4

Dry Heat

Answer 4

1. Flaming of inoculating loops
2. Incineration - nothing sharp (needles)
3. Hot-air sterilization: 170c for 2 hours.

Question 5

Filtration

Answer 5

1. Vaccines, enzymes, antibodies
2. Mask (N95)
3. O.R. burn units use this.

Question 6

Ionizing Radiation

Answer 6

1. Process. Radiation ionizes H20 - forms OH+ - damages DNA
2. Hospital settings that use this
   - pharmaceuticals
   - dental supplies
   - medical supplies like sutures

Question 7

Non-ionizing Radiation

Answer 7

Forms T=T (double bonded thiamine) dimers that damage the DNA.
Used in: 
- Nurseries
- Cafeterias
- O.R's

Question 8

Phenols

Answer 8

Phenol - Phenolics

eg. Lysol

Question 9

Halogens

Answer 9

I2 - iodophor - attaches to tyrosine - di-iodo-tyrosine
The process of iodophor attaching to tyrosine causes denaturation and cell death.

Cl2 + H2O = HOCl
this is a redox reaction

Question 10

Alcohols

Answer 10

1. Ethanol: use 70-30% instead of 100% because it’s more effective
2. Isopropanol

Question 11

Quats

Answer 11

Ammoniums
H
H - N - H
H

Question 12

Gas

Answer 12

Ethylene Oxide

H2C - CH2
    \        /
        O
\+ Proteins
- The proteins denature
Used for:
- Machines
- Dialysis
- Respirators
- Mattresses