chapter 7- the control of microbial growth

Sterilization

the removal or destruction of all living microorganisms.

Heat

most common method used for killing microbes, including the most resistant forms such as endospores.

Sterilant

sterilizing agent

Commercial sterilization

limited heat treatment (canned food)

enough heat to destroy Clostridium Botulinum (can produce deadly toxins)

retorted (canned) soups, meats, and vegetables; aseptic milk; and vacuum-packed fish

Disinfection

control directed at destroying harmful microorganisms. destroy vegetative (non-endospore-forming) pathogens

alcohols (70% isopropyl), chlorine bleach solutions

Antisepsis

When disinfectant is directed at living tissue (chemical is called antiseptic)

washing hands with alcohol-based gel

mouthwash

Degerming

which mostly results in the mechanical removal rather than killing of most of the microbes in a limited area.

Washing hands with soap and water

Sanitization

which is intended to lower microbial counts to safe public health and minimize the chances of disease transmission to another user.

Restaurant glassware

biocide/germicide

kills microorganisms

fungicide kills fungi; a virucide inactivates viruses; and so on

bacteriostasis

Once a bacteriostatic agent is removed, growth might resume.

sepsis

indicates bacterial contamination, as in septic tanks for sewage treatment. a life-threatening, dysregulated host response to infection.

asepsis

is the absence of significant contamination (see Chapter 1). Aseptic techniques are important in surgery to minimize contamination from the instruments, operating personnel, and the patient.

Thermal Death Point (TDP)

is the lowest temperature at which all the microorganisms in a particular liquid suspension will be killed in 10 minutes.

Thermal death time (TDT)

the minimal length of time for all bacteria in a particular liquid culture to be killed at a given temperature.

Decimal Reduction Time (DRT)

is a third concept related to bacterial heat resistance.

is the time, in minutes, in which 90% of a population of bacteria at a given temperature will be killed

Autoclave

a pressure chamber used to sterilize equipment, media, and waste by utilizing high-pressure saturated steam

Pasteurization

a heat-treatment process that destroys pathogens and spoilage microorganisms in food and beverages.

prolongs milk’s good quality under refrigeration.

Thermoduric

Heat resistant bacterias which causes milk to spoil overtime.

Ultra high temperature treatments (UHT)

sterilizes liquid foods, most commonly milk, by heating them to 135–150°C (275–302°F) for 2 to 5 seconds. This process kills all bacterial spores, allowing the product to be shelf-stable for 6–12 months without refrigeration when paired with aseptic packaging.

Dry heat sterilization

Direct flaming

Hot air sterilization

a temperature about 170C maintained for 2 hrs ensures sterilization

High efficiency particulate air (HEPA) filters

removes almost all microorganisms larger than about 0.3 um in diameter.

Membrane filters

composed of such substances as cellulose esters or plastic polymers

Regular refrigeration

has a bacteriostatic effect

High pressure

it alters the molecular structures of proteins and

carbohydrates, resulting in the rapid inactivation of vegetative

bacterial cells.

Fruit juices preserved by high-pressure treatments

Desiccation

absence of water

can remain viable for years

Osmotic pressure

directly impacts microbial growth by controlling water availability.

salted meat, jam, honey, and brine-pickled vegetables

Ionizing radiation

carries more energy

gamma rays, X rays, and high-energy electron beams has a wavelength shorter

Nonionizing radiation

has a wavelength longer

ultraviolet (UV) light. UV light damages the DNA of exposed cells

Sunlight

Microwaves

1. Moist heat

a. Boiling or flowing steam

b. Autoclaving 

2. Pasteurization 

Protein denaturation

Mechanism of actions -dry heat and direct flaming

Burning contaminants to ashes

Incineration

Burning to ashes

Hot air sterilization

Oxidation

MOA Filtration

Separation of bacteria from suspending liquid

Refrigeration

Deep freezing

Lyophilization

Decreased chemical reactions and possible changes in proteins

MOA High pressure

Alteration of molecular structure of proteins and carbs

MOA Desiccation

Disruption of metabolism

MOA osmotic pressure

Plasmolysis

MOA Ionizing radiation

Destruction of DNA

Nonionizing

Damage to DNA

Phenol and phenolics

Disruption of plasma membrane, denaturation of enzymes

Lister was the first to use this to control surgical infections in the operating room

Halogens

Iodine inhibits protein function and is a strong oxidizing agent;

chlorine forms the strong oxidizing agent hypochlorous acid, which alters cellular components

Alcohols

Protein denaturation and lipid dissolution

kills bacteria and fungi but not endospores and nonenveloped viruses.

Heavy metals

Denature of enzymes and other essential proteins

Silver, mercury and copper for hospital infections

Soaps and detergents

Mehanical removal of microbes through scrubbing.

mechanical removal through scrubbing

Quaternary Ammonium Compounds

Enzyme inhibition, protein denaturation and disruption of plasma membranes.

Aldehydes

Protein denaturation

among the most effective antimicrobials. inactivate proteins by forming covalent cross links with several organic functional groups on proteins

Peroxygens

Oxidation

group of oxidizing agents that includes hydrogen peroxide and peracetic acid.

Disinfectants

Phenol & phenolics

Heavy metals

Soap and detergents

Antiseptics

Quats

Antibiotics

Aseptides

Peroxygen

Disinfectants vs Antiseptics

-Mainly used for cleaning surfaces and killing microbes on non-living objects

-Are used on living tissues to prevent infection.