Module 4: Physical and Chemical Growth Control

Question 1

5 Methods of Controlling Microbial Growth (Physical and Chemical)

Answer 1

1. Heat Sterilization
2. Pasteurization
3. Radiation
4. Filtration
5. Chemicals

Question 2

Decontamination Definition

Answer 2

Inhibit the growth of microbes
-cidal : kill
-static : inhibits

Question 3

Decimal Reduction Time (D)

Answer 3

Time required at a given temperature for a tenfold reduction in the viability of a microbial population

Question 4

Thermal Death Time (TDT)

Answer 4

Time it takes to kill all cells at a given temperature

Question 5

4 Factors affecting Thermal Death Time

Answer 5

1. Presence of endospore forming bacteria
2. Medium in which heating takes place
3. Concentration of sugars proteins and fats
4. Concentration of salt

Question 6

Two molecules present in endospores that improve heat stability

Answer 6

1. Dipicolinic Acid (Ca+ complex)
2. Small-acid Soluble Proteins (SASP)

Question 7

D(endospore)
D(vegetative)
Time and temperature to reach 1/10th *

Answer 7

D(endospore) - 4-5 mins @ 121 degrees celsius
D(vegetative) - 0.1-0.5 @ 65 degrees celsius

Question 8

Dry Heat vs Moist Heat

Answer 8

DRY HEAT
- slow heat and steam production
- sterilizes glasswear
- flame sterilization
- hot or correction areas
- 160-120 degrees celsius for 1-16 hours

MOIST HEAT
- higher heat and steam production
- produces faster D
- Autoclaves
- 121 degrees celsius, for 15 Psi, for 15-20 minutes

Question 9

Autoclave conditions

Answer 9

20-30 minutes
121 degrees celsius
15 Psi

Question 10

3 Types of Pasteurization

Answer 10

1. Flash Pasteurization
   - controlled milk flow rate
   - 71 degrees for 15s
2. Holding Pasteurization
   - not palatable for most consumers
   - 62 degrees for 30mins
3. Ultrahigh Temperature
   - 74 degrees –> 140 degrees –> 74 degrees for <5s

Question 11

4 Types of Low temperatures

Answer 11

1. Refrigeration
   - ~5 degrees
2. Freezing
   - ~-20 degrees
3. Drying
   - absence of water inhibits enzymatic activities
4. Freeze-Drying
   - LYOPHILIZATION: process in which water in the form of ice under low pressure is removed from a material by sublimation

Question 12

2 Types of Radiation

Answer 12

1. Ultraviolet light
   - 220-300nm
   - causes breaks and modifications in DNA resulting in cell death
   - may become ineffective because of activated repair mechanisms
   - limited to disinfecting exposed surfaces
2. Ionizing Radiation
   - X-rays & gamma rays
   - highly reactive molecules that can destroy DNA, lipids and proteins resulting in cell death
   - measured in ROENTGEN (radiation absorbed per g of tissue)

Question 13

LYOPHILIZATION

Answer 13

: process in which water in the form of ice under low pressure is removed from a material by sublimation

Question 14

2 Types of Filtration

Answer 14

1. Depth Filters
   - fibrous sheath of randomly overlapping paper or borosilicate fibers
   - HEPA filters
2. Membrane Filters
   - most commonly used in liquid sterilization
   - high tensile strength polymers
   - syringe + pump + collecting vessel
   —> NUCLEATION TRACK/NUCLEOPORE: uniformly-sized pores; isolate specimen for SEM

Question 15

3 types of Chemical Growth Rate Control

Answer 15

1. Bacteriostatic
   - inhibitors of protein synthesis
   - viable and total cells are the same
2. Bactericidal
   - binds to cellular target; kills it
   - viable cell count is lower than total cell count
3. Bacteriolytic
   - kills cells via cell lysis
   - viable and total cells are the same (but both decreasing)

Question 16

Measuring Antimicrobial Activity (2)

Answer 16

1. Disc Diffusion Technique
   (i) inoculate plate w/ test organisms
   (ii) discs containing antimicrobial agents are placed on surface
   (iii) test organisms demonstrates “zone of inhibition”
2. Minimum Inhibitory Concentration
   - tube dilation technique
   - smallest amount of agent to inhibit microbial growth (clear test tube)

Question 17

4 Factors affecting MIC

Answer 17

1. Bacterial species
2. Inoculum size
3. Culture medium
4. Incubation conditions

Question 18

Antiseptics & Germicides

Answer 18

Nontoxic agents that can kill/inhibit growth of organisms; LIVING TISSUE

Question 19

Disinfectants

Answer 19

Kills organisms; INANIMATE ORGANISMS

Question 20

Sanitizers

Answer 20

Reduces microbial numbers

Question 21

Sterilant

Answer 21

Destroy all forms of microorganisms

Question 22

PHENOLS & PHENOLICS

Answer 22

• antiseptic
• mode of action:
  i) disrupts cytoplasmic membrane
  ii) denatures DNA
  iii) inactivates enzyme
• soaps, lotions, cosmetics, body deodorant

Question 23

HALOGENS

Answer 23

• sterilant, disinfectant, sanitizer
• modes of action:
  i) iodine binds to tyrosine residues of proteins; inhibits protein production
  ii) iodine oxidizes sulfhydryl groups; disrupts protein structure
  iii) Water + Cl = oxidizing agent (hypocholorous acid)
• topical antiseptic, disinfectant of lab surfaces

Question 24

ALCOHOLS

Answer 24

-antiseptic (@70%)
- Mode of actions
i) denatures proteins (w/ water)
ii) disrupts cellular membrane
iii) lipid solvent
- topical antiseptic

Question 25

Quaternary Ammonium Compounds

Answer 25

- Disinfectant, antiseptic, sanitizer - Mode of actions: i) disrupts the membrane ii) interacts with phospholipids - medical food and dairy equipment; soaps lotion topical disinfectant - support the growth of Psuedomonas sp.

Question 26

ALKYLATING AGENTS

Answer 26

- disinfectant, sterilant - Modes of action: i) disrupts proteins and structure of nucleic acids - surface disinfectant, sterilant for temp-sensitive materials (plastics); high level disinfectant for medical instruments

Question 27

OXIDIZING AGENTS

Answer 27

- antiseptic, disinfectant, sterilant - Modes of action: i) membrane and protein stability