Control of Microbial Growth

Question 1

Sterilization

Answer 1

The killing or removal of all viable organisms within a growth medium

Question 2

Inhibition

Answer 2

• Effectively limiting microbial growth
• No killing taking place

Question 3

Decontamination

Answer 3

The treatment of an object to make it safe to handle

Question 4

Disinfection

Answer 4

• Directly targets the removal of all pathogens
• Not necessarily all microorganisms

Question 5

Heat Sterilization

Answer 5

is the most widely used
method of controlling microbial growth

Question 6

Endospores

Answer 6

Can survive heat that would rapidly kill vegetative cells

Question 7

Pasteurization

Answer 7

is the process of using precisely controlled heat to
reduce the microbial load in heat-sensitive liquids
- Does not kill all organisms-> not sterilization

Question 8

Autoclave

Answer 8

The autoclave is a sealed device that uses steam under pressure
- Allows temperature of water to get above 100℃

Question 9

Radiation

Answer 9

• Physical method of growth control
• Microwaves, UV, X-rays, gamma rays, and electrons can reduce microbial growth
• UV has sufficient energy to cause modifications and breaks in DNA
• UV is useful for decontaminating surfaces
• Cannot penetrate solid, opaque, or light-absorbing surfaces

Question 10

Ionizing radiation

Answer 10

Electromagnetic radiation that produces ions and other reactive molecules generates electrons, hydroxyl radicals,
and hydride radicals
- Some microorganisms are more resistant to radiation than others.
- amount of energy required to reduce viability tenfold is analogous to D value

Question 11

Filtration

Answer 11

avoids the use of heat on sensitive liquids and gases
- Pores of filter are too small for organisms to pass through
- Allow liquid or gas to pass through
- Ex) HEPA filters, membrane filters

Question 12

Membrane Filters

Answer 12

Filtration can be accomplished by:
- Syringe
- Pump
- Vacuum

Question 13

How can antimicrobial agents be classified?

Answer 13

1. Bacteriostatic: prevents cell growth as long as the antimicrobial agent is
   present
2. Bacteriocidal: kills the cells (does not lyse them)
3. Bacteriolytic: kills and lyses the cells

Question 14

Minimum inhibitory concentration (MIC)

Answer 14

• The smallest amount of an agent needed to inhibit
  growth of a microorganism
• Varies with the organism used, inoculum size,
  temperature, pH, etc.
• Increasing concentration of antibiotic from left to
  right.
• Lowest concentration with no growth = MIC
• May still have living (non-growing) organisms
• i.e. the antibiotic may be bacteriostatic

Question 15

Minimal Lethal Concentration (MLC)

Answer 15

• Plate aliquots of broth from the MIC and from tubes with higher concentrations of antibiotic, on appropriate nutrient agar plates, without antibiotic
• Do colonies form? No colonies = Minimal Lethal Concentration (MLC)
• MLC usually higher than MIC

Question 16

Disc diffusion assay

Answer 16

• Uses solid media
• Antimicrobial agent is added to filter paper disc
• The MIC is reached at some distance
• Forms a zone of inhibition
• Area of no growth around disc

Question 17

What the two categories antimicrobial agents can be divided into?

Answer 17

1. Products used to control microorganisms in commercial and industrial applications
2. Products designed to prevent growth of human pathogens in inanimate
   environments and on external body surfaces

Question 18

Products used to control microorganisms in commercial and industrial applications

Answer 18

Ex) chemicals in foods, air conditioning cooling towers, textile and paper
products, fuel tanks

Question 19

Products designed to prevent growth of human pathogens in inanimate
environments and on external body surfaces

Answer 19

• Sterilant: destroys all microorganisms including endospores
• Disinfectant: kills microorganisms but not all endospores.
  
  • Used on inanimate objects
• Sanitizer: reduces the numbers of microorganisms on surfaces (e.g. hand
  sanitizers)
• Antiseptic: kills or inhibits the growth of microorganisms (non-toxic enough to be applied on living tissue (e.g. mouth wash))