Chatper 7- The Control of Microbial Growth

Question 1

Sterilization

Answer 1

destroys all forms of life

Question 2

commercial sterilization

Answer 2

sufficient heat treatment to kill C. botulinum endospores in canned food

Question 3

disinfection

Answer 3

treatment used to kill bacteria on objects

Question 4

antisepsis

Answer 4

treatment to kill bacteria on tissue

Question 5

degerming

Answer 5

removing microbes from a limited area

Question 6

sanitization

Answer 6

removing microbial counts on eating utensils

Question 7

sepsis

Answer 7

presence of a toxin or pathogen in blood/tissue

Question 8

asepsis

Answer 8

the absence of contamination by unwanted bacteria

Question 9

factors that influence effectiveness of microbial control agents

Answer 9

# of microbes
presence of organic matter
temperature (heat is more effective in acidic conditions, heat is less effective against microbes in the presence of fats and proteins)
time exposure 
microbial characteristics

Question 10

actions of microbial control agents

Answer 10

damage to the cell membrane (susceptible due to lipid/protein components)
damage to proteins and nucleic acids

Question 11

Methods of control

Answer 11

Physical: Moist heat (denatures proteins), pasteurization, dry heat (coagulates proteins, dries cells, oxidizes), filtration, cold, high pressure, desiccation, radiation. And chemical

Question 12

Thermal Death Point

Answer 12

lowest temperature where all microbes in a liquid will be killed in 10 minutes.

Question 13

thermal death time

Answer 13

length of time required to kill all bacteria in a liquid culture at a given temperature

Question 14

decimal reduction time

Answer 14

length of time required to kill 90% of a bacterial population at a given temperature

Question 15

pasteurization

Answer 15

eliminates pathogens/reduces spoilage organisms

equivalent treatments 63 C for 30 min, HTST(72C for 15 sec)

Question 16

Dry heat sterilization

Answer 16

examples are hot-air sterilization, direct flaming to a red glow, and incineration.

Question 17

filtration

Answer 17

• High-efficiency particulate Air (HEPA) filters remove microbes larger than 0.3 microns
• membrane filters remove microbes more than 0.22 microns or even 0.01 microns

Question 18

Low temperatures on microbial growth

Answer 18

refrigeration (0-7C) is bacteriostatic as even psychrotrophs will still grow slowly and eventually alter food.

deep-freezing usually renders them dormant without killing them. However, ice crystals can be formed which will disrupt structure( slow freezing is more harmful than rapid)

Question 19

high pressure on microbial growth

Answer 19

Very high pressure for 3-5 min applied to a liquid suspension is instantly transferred equally through a food package. This can cause denaturation of proteins, phospholipid gelation, and irreversible damage resulting in loss of membrane. This method can be used for food because is doesn’t use heat (while it inactivates most vegetative cells, it doesn’t work on endospores)

Question 20

Desiccation

Answer 20

metabolism is prevented but cells can remain viable.

Resistance: endospore>viruses>vegetative cells

Question 21

Osmotic pressure on microbial growth

Answer 21

high salt/sugar concentrations create hypertonic conditions which will cause the cell to crenate. However, yeast/molds are much better at growing on low moisture/high osmolarity foods).

Question 22

Radiation

Answer 22

Ionizing(X-rays, gamma, high energy electron beams): ionize H2O to release hydroxyl radicals that will react with cell components.

Nonionizing (UV, 260nm): causes thymine dimers

Microwaves kill by heat

Question 23

Phenol

Answer 23

significant bacteriocidal effects above 1%, but rarely used because it irritates skin; it works by injuring the cell membrane.

Question 24

Phenolics

Answer 24

derivatives of phenol that were made to reduce irritation and increase antimicrobial effects (active in presence of organics, stable, persist long after application)

Question 25

Bisphenols

Answer 25

made up of two phenolic groups covalently linked, disrupts membrane. However, triclosan inhibits enzyme needed for biosynthesis of fatty acids.

Question 26

Biguanides

Answer 26

broad spectrum (same as bisphenols), disrupt cell membrane, used as surgical hand scrubs when combined with alcohol or detergent. (Examples are chlorhexidine and alexidine)

Question 27

Iodine

Answer 27

complexes with unsaturated fatty acids and amino acids to disrupt the membrane and impair protein synthesis, respectively. available as a tincture (in aqueous alcohol) or as an iodophor (combined with an organic molecule so they do not stain or irritate).

Question 28

Chlorine

Answer 28

when added to water, chlorine becomes HOCl which oxidizes proteins, nucleic and fatty acids, and is effective because it can diffuse through the membrane as quickly as water. *effective against endospores and cytsts at high concentrations.

Question 29

Alcohols

Answer 29

Kills by denaturing proteins and dissolving lipids, but it requires water for denaturation (so it us usually a bit diluted with water). They bolster the effects of tinctures. However, they are not effective against spores or non-enveloped viruses.

Question 30

Heavy metals

Answer 30

Very few amounts are necessary for antimicrobial action. They denature proteins by combining with sulfhydryl groups.

Question 31

Soaps and detergents

Answer 31

little value as an antiseptic but assist in degerming by removal with scrubbing.

Question 32

Acid-anionic detergents

Answer 32

Used at low pH. The anion reacts with the plasma membrane and are used for cleaning dairy equipment.

Question 33

Quarternary ammonium compounds (cationic detergents)

Answer 33

Kills fungi, protozoans, bacteria (more effective against Gram + than Gram -) and enveloped viruses. disrupts plasma membrane, denatures proteins.

Question 34

Sodium benzoate/Potassium Sorbate

Answer 34

bacterio/fungistatic in cheese and soft drinks.

Question 35

calcium proprionate

Answer 35

inhibit mold growth (fungistatic) by interfering with the mold’s metabolism or integrity of the membrane.

Question 36

Sulfur dioxide

Answer 36

preservative for wine/dried fruits. inhibits microbial growth

Question 37

nitrates/nitrites

Answer 37

Prevents endospore formation by C. botulinum by binding to iron-containing enzymes.

Question 38

Nisin

Answer 38

added to cheese; effective in many gram + organisms and spores.

Question 39

Natamycin

Answer 39

active against fungi

Question 40

Aldehydes

Answer 40

Among the most effective Inactivates proteins by cross-linking with functional groups (NH2, OH, COOH, SH)

formaldehyde is used with water
glutaraldehyde is less irritating but more effective than formaldehyde and when in 2% solution, it’s bactericidalm tuberculocidal, and virucidal in 10 min. It is sporicidal in 3-10 hours.

Question 41

Chemo-sterilants

Answer 41

requires a closed chamber and is used for heat-sensitive material. Ethylene oxide alkylates by replacing the protein’s labile hydrogen atoms with a radical. (chlorine dioxide also achievees this).

this requires long exposures and is toxic/explosive when in pure form.

Question 42

Plasma

Answer 42

ionized gas that can sterilize almost any material

Question 43

peroxygens

Answer 43

• H2O2- disinfects inanimate objects and can be sporicidal at high concentrations. sterilant as a heated gas
• peracetic acid- effective on endospores and viruses within 30 min and is fungicidal/bactericidal in 5 min. sterilant
• Ozone generated by passing oxygen through high-voltage electrical discharges. supplements chlorine in H2O disinfection and is more effective, but difficult to maintain residual activity in H2O.

Question 44

How do you get rid of prions?

Answer 44

autoclaving with sodium hydroxide at 134 C, or incineration.