Exam 2 Physical and Chem Control 10/12

Question 1

sterilization

Answer 1

destruction or removal of all viable organisms
Sterilants

Question 2

disinfection

Answer 2

killing, inhibition, or removal of disease causing organisms
Disinfectants

Question 3

sanitization

Answer 3

reduction of microbial population

Question 4

antisepsis

Answer 4

Destruction or inhibition of microorganisms on living tissue
Antiseptics

Question 5

chemotherapy

Answer 5

use of chemicals to kill or inhibit growth of microorganisms within host tissue

Question 6

agents that kill microorganisms or inhibit their growth

Answer 6

cidal agents kill
static agents inhibit growth

Question 7

The Pattern of Microbial Death

Answer 7

microorganisms are not killed instantly

population death usually occurs exponential

measure of agent’s killing efficiency
decimal reduction time (D-value) – time to kill 90% of microorganisms and spores in a sample under specific conditions

Question 8

Conditions Influencing the Effectiveness of Antimicrobial Agent Activity

Answer 8

1) population size
larger populations take longer to kill than smaller populations

2) population composition
microorganisms differ markedly in their sensitivity to antimicrobial agents

3) concentration or intensity of an antimicrobial agent
usually higher concentrations or intensities kill more rapidly (not always, e.g., EtOH)
relationship is not linear

4) Contact time - duration of exposure
longer exposure  more organisms killed

5) temperature
higher temperatures usually increase amount of killing

6) local environment
many factors (e.g., pH, viscosity, and concentration of organic matter) can profoundly impact effectiveness

Question 9

Physical Control Methods

Answer 9

Filtration
Heat
Radiation

Question 10

Filtration

Answer 10

Physical removal of microbes by filtration
Filtration has been a method of purifying liquids for centuries
Lab applications use membrane nylon/Teflon filters with a pore size of 0.2 or 0.45 μm
Viruses can be removed from liquids by ultrafiltration methods (reducing pore size 10 to 100 nm)

Problems can result, though…
Large particles clog filters.
Ultrafiltration requires high pressure.
Viscous liquids don’t filter well.

Question 11

Membrane Filter Sterilization

Answer 11

-Removes microorganisms from heat sensitive liquids

Question 12

Biological Safety Cabinet and other filtration devices

Answer 12

N-95 masks removes 95% of particles 0.3um or larger

high-efficiency particulate air (HEPA) filters
used in laminar flow biological safety cabinets
Removes 99.97% of particles 0.3 um or larger

Question 13

Temperature

Answer 13

Heat
-proteins and nucleic acids disrupted

Freezing
-Can damage cells by forming ice crystals
-Can stop biochemical reactions in microbes

Question 14

Steam Sterilization

Answer 14

must be carried out above 100oC which requires saturated steam under pressure

carried out using an autoclave (Developed by Chamberland, 1884)

(121 C at 15 psi for 10-15 min)

effective against all types of microorganisms including spores
*^ spores usually have a harder time living in high pressure vs just high temperature, so to sterilize we need to apply pressure

quality control – indicator tape or ampules of Geobacillus stearothermophilus

Question 15

Tyndallization

Answer 15

Developed by John Tyndall

Intermittent sterilization

30-60 min of steam repeated 3 times with 23-24 hr incubations between

Used to kill spores – spores germinate and are then killed by the steam treatment

Question 16

Pasteurization

Answer 16

controlled heating at temperatures well below boiling (55 - 60 C)

used for milk, beer, and other beverages

process does not sterilize but does kill pathogens present and slows spoilage by reducing the total load of organisms present

Introduced to US in 1889

Question 17

Dry Heat Sterilization

Answer 17

less effective than moist heat sterilization, requiring higher temperatures and longer exposure times
items subjected to 160–170oC for 2 to 3 hours
E.g., C. botulium – 5 min at 121C or 2 hrs at 160C

oxidizes cell constituents and denatures proteins

Question 18

Dry Heat Incineration

Answer 18

bench top incinerators are used to sterilize inoculating loops used in microbiology laboratories

Question 19

Radiation-UV

Answer 19

Using electromagnetic radiation to control microbes

UV radiation of 260 to 280 nm wavelengths can damage DNA, forming thymine dimers.

Question 20

Ionizing Radiation

Answer 20

gamma radiation penetrates deep into objects

destroys bacterial endospores; not always effective against viruses

used for sterilization and pasteurization of antibiotics, hormones, sutures, plastic disposable supplies, and food

Question 21

Chemical Control Agents

Answer 21

Disinfection
Antisepsis
Sterilization

Question 22

Chemical Methods:

Answer 22

Chemical methods of controlling microbes

Disinfectants: Chemicals used on non-living surfaces to kill pathogenic microbes.

Antiseptics: Chemicals that can be used on living tissue to kill pathogenic

Question 23

What makes a good chemical agent?

Answer 23

Should kill a wide-range of microbes
Shouldn’t be corrosive or overly toxic
Shouldn’t leave a residue
Shouldn’t emit fumes or smell TOO bad
Should be cheap
Should be temperature stable

Question 24

Which Method to use?

Answer 24

How do you pick a method?

What microbes are present? What about endospores?
How many microbes are present? Do they all need to die?
What kind of object needs to be treated?
If using a physical method, how long/intense does it need to be?
If using a chemical method, how powerful must it be, and how long does it need to be applied?
Do we need to worry about toxicity to humans or other life?

Question 25

Phenolics

Answer 25

Phenol was 1st widely used antiseptic and disinfectant. Used in 1867 by Joseph Lister
commonly used as laboratory and hospital disinfectants (e.g., Lysol)
act by denaturing proteins and disrupting cell membranes
tuberculocidal, effective in presence of organic material, and long lasting
disagreeable odor and can cause skin irritation
E.g., triclosan is used in hand sanitizers

Question 26

Aldehydes

Answer 26

commonly used agents are formaldehyde and glutaraldehyde
highly reactive molecules
sporicidal and can be used as chemical sterilants
combine with and inactivate nucleic acids and proteins

Question 27

Alcohols

Answer 27

among the most widely used disinfectants and antiseptics
two most common are ethanol and isopropanol (60 – 80 %)
not sporicidal
inactivate some viruses
denature proteins and possibly dissolve membrane lipids

Question 28

Halogens - Iodine

Answer 28

skin antiseptic

oxidizes cell constituents and iodinates proteins

at high concentrations kills spores

skin damage, staining, and allergies can be a problem

iodophore

Question 29

Halogens - Chlorine

Answer 29

oxidizes cell constituents

destroys vegetative bacteria and fungi,

chlorine gas is sporicidal

can react with organic matter to form carcinogenic compounds

E.g., Bleach is highly effective (10% with a little vinegar)

Question 30

Heavy Metals

Answer 30

e.g., ions of mercury, silver, arsenic, zinc, and copper

effective but usually toxic

combine with and inactivate proteins; may also precipitate proteins

Question 31

Quaternary Ammonium Compounds

Answer 31

amphipathic organic cleansing agents
act as wetting agents and emulsifiers
Disrupt membranes and denature proteins
kill most bacteria, but not Mycobacterium tuberculosis or endospores
safe and easy to use, but inactivated by hard water and soap

Question 32

Evaluating a disinfectant

Answer 32

Disk-diffusion method

Question 33

Sterilizing Gases

Answer 33

used to sterilize heat-sensitive materials like plastics

microbiocidal and sporicidal

ethylene oxide sterilization is carried out in equipment resembling an autoclave

EtO is a very strong alkylating agent

betapropiolactone and vaporized hydrogen peroxide

Question 34

Which physical or chemical agents would be the best choice for sterilizing the following items: glass pipettes, tryptic soy broth tubes, antibiotic solution, plastic-wrapped Petri plates?