Chapter 7: The Control of Microbial Growth

sterilization

complete removal of all microorganisms (including endospores) and viruses from an object or surface

disinfection

reducing the number of microorganisms on a surface so that the risk of infection is minimized

disinfectant

antimicrobial agent that is applied to inanimate (non-living) objects only

antiseptic

antimicrobial agent that can be applied to living tissue

general categories of antimicrobial agents

• sanitizer

• bacteriostatic agent

• bactericidal agent or bactericide

• fungicide

• viricide

sanitizer

antimicrobial agent used to reduce the number of microorganisms on food-handling equipment and utensils

bacteriostatic agent

substance that inhibit growth of (but does not kill) bacteria

bactericidal agent or bactericide

antimicrobial agent that kill bacteria but not necessarily endospores

fungicide

chemical agent that kills fungi

viricide

chemical agent that destroys viruses

the effectiveness of an antimicrobial agent depends on the

1. number of microorganisms present, including whether they have formed a biofilm

2. environmental conditions (temperature, pH, salinity)

3. length of time of exposure

4. degree of microbial resistance

actions of antimicrobial agents

1. damage to cell membrane: some agents, such as surfactants, alter membrane permeability, making membranes “leaky”

2. damage to proteins: denaturation of proteins can be permanent (bactericidal) or temporary (bacteriostatic)

3. damage to nucleic acids: alkylating agents are chemical mutagens that alter nucleic acids. some are carcinogenic/cancer-causing (formaldehyde)

microorganism resistance to antimicrobial killing

least resistant —>most resistant

viruses, gram positive bacteria, viruses without envelopes, fungi (including fungal spores), gram-negative bacteria, vegetative protozoa, cysts of protozoa, mycobacteria, endospores of bacteria, prions

type of disinfectants

phenols/phenolics, iodine, chlorine, alcohols, and heavy metals

phenol/phenolic antimicrobial action

disrupt plasma membrane

iodine antimicrobial action

damage to membranes and alters protein synthesis

chlorine antimicrobial action

oxidizing agent that inhibits enzymatic functions

alcohols antimicrobial action

dissolves lipids (membrane damage) and denatures proteins

heavy metals antimicrobial action

denatures proteins

examples and uses of phenol/phenolics

lysol spray

examples and uses of iodine

tincture- iodine in aqueous alcohol and betadine

examples and uses of chlorine

hypochlorous acid (HOCI) added to water

examples and uses of alcohols

ethanol and isopropanol (isopropyl alcohol)

examples and uses of heavy metals

silver, mercury, and copper

types of surfactants (disinfectants)

soaps and detergents (anionic and cationic)

other types of disinfectants

aldehydes and peroxygens

antimicrobial action of soaps

physically washes away bacteria

antimicrobial action of anionic and cationic detergents

damage to membrane

antimicrobial action of aldehydes

inactivate proteins by reacting covalently with functional groups

antimicrobial action of peroxygens

oxidizing agent

examples and uses of soaps

body soap

examples and uses of detergents

laundry detergent and dish soap or mouth wash

examples and uses of aldehydes

glutaraldehyde and formaldehyde used to sterilize medical equipment

examples and uses of peroxygens

ozone and hydrogen peroxide. used to sterilize or decontaminate surfaces

types of chemical food preservatives

organic acids, sodium nitrite, and antibiotics

antimicrobial action of organic acids

inhibit metabolism

antimicrobial action of sodium nitrite

prevents endospore formation

antimicrobial action of antibiotics

prevents endospore formation and prevents mold

examples and uses of organic acids

sorbic acid, sodium benzoate, calcium propionate. controls growth of molds and bacteria in food and cosmetics

examples and uses of sodium nitrite

prevents endospore formation. in hot dogs, sausage, ham, and bacon

examples and uses of antibiotics

only nisin and natamycin added to dairy

types of physical methods of inhibiting microbial growth

temperature, filtration, desiccation, and osmotic pressure

notes for heat sterilization

denatures proteins. dry heat- slower than moist heat. moist heat- quickly penetrates and kills cells.

notes for pasteurization

denatures proteins. reduces number of pathogens and microorganisms but is not sterilization

notes for low temperature

decreased enzymatic activity. refrigeration (4 degrees C), freezing (-20 to 80 degrees C), lyophilization (freeze-drying)

notes for filtration

physical removal of bacteria from gas/liquid, HEPA filters- gasses, membrane filters- liquids

notes for desiccation

inhibits enzyme activity

notes for osmotic pressure

plasmolysis

uses of heat sterilization

dry powders and microbial medium

uses of pasteurization

milk, consumable liquids

uses of lower temperature

refrigerated foods

uses of filtration

BSL- 4 facility and liquid medium

uses of desiccation

dried cereal, dehydrated milk

uses of osmotic pressure

jams, sausage

types of radiation

ionizing, nonionizing, and microwave

notes on ionizing radiation

DNA destruction, destroys DNA through free radicals (X rays, gamma rays, electron beams)

notes on nonionizing radiation

DNA damage and ultraviolet (UV) radiation damages DNA by forming thymine dimers

notes of microwaves

heat, vegetative bacteria are killed by heat

uses of ionizing radiation

medical equipment, drugs, mail, tissue grafts

nonionizing radiation uses

UV lamp used in hospitals and laboratories

uses of microwave radiation

foods