Sterilization

The destruction or removal of all microbial life, including endospores.

Disinfectant

Any treatment used on inanimate objects to kill or inhibit the growth of microorganisms; removing pathogens. Doesn't kill spores.

Sanitization

The removal of microorganisms from eating utensils and food preparation areas.

Decontaminate

to make (an object or area) safe for unprotected personnel by removing, neutralizing, or destroying any harmful substance, as radioactive material or poisonous gas

We wish to control microbes under these two conditions

1. Destroy and reduce the transmission of pathogens

2. Reduce or eliminate contaminating microbes from food, water, special areas, etc.

De-germ

the removal of microorganisms from an area

Septic

infected with a toxic or pathogenic organism in the blood or tissue, especially in respiratory or urinary tracts

Aseptic

free from pathogenic organisms (especially on skin) that cause disease or infection

free from contamination

2 main chemical disinfecting agents that kill microorganisms or inhibit their growth

1. - cides
2. - static

- cides

agents which kill microbes

-static

Stops microbes from growing but do not kill them. The microbes are there and if you take the treatment away, they can resume growth.

Germicides

kill microorganisms and viruses, but not necessarily endospores

Alcohol kills microbes best at what %?

70%

Endospore

protective structure to endure environmental stress

Most resistant organism to being killed

prions

Microbes are considered to be dead when ______

they are unable to reproduce in conditions that normally support their reproduction

How do microbes die?

When you spray down a counter top, they're not all killed immediately.

Adding disinfectant in stationary phase makes death phase start the exponential decrease. This decrease will differ depending on the microbe.

When a population has been greatly reduced, the rate of death may slow due to survival of resistant organisms.

exponential decrease

The population will be reduced by the same fraction in each time interval

D-value

Decimal reduction value. Also called D process.

Time required to kill 90% of the microbial population under specific conditions at that particular dose.

the dose of the disinfectant and how long you have to expose it for your # of microbes to be reduced by a power of 10.

1 D-process reduces the number of microbes by ______

one exponent

Use-dilution Test

Where you set up microbes in liquid culture and add to that culture different concentrations of your test disinfectant. Determine MIC or MBC.

MIC

Minimum inhibitory concentration. What is the minimum dose we need to have to prevent microbial growth> Doesn’t tell you one particular aspect: did we kill the microbes or did we just stop them from growing?

MBC

After MIC, the second step you can do as an add on is take the cultures that don’t look like they have microbes growing in them and dilute them into fresh media so its been diluted down to where the disinfectant is not going to work and we will see if the microbe grows back. Then we can determine the concentration we need to kill the microbes. Not just make sure it slows down and stops growing but gets killed.

Dilution factor

how much can you dilute it?

5 disinfectant considerations

1. Dilution factor
2. Time of exposure
3. Target microbes
4. Cost
5. Surfaces of interest

Time of exposure

How long does it take for you to kill off the microbes? If you have to wipe down the counter for 30 minutes, its not useful.

Target of microbes

Making sure it kills the microbes you care about.

Surfaces of interest

Making sure it doesn’t degrade or have nasty effects on to whatever surface.

Disk-Diffusion Method

We use the size of that zone of inhibition to compare how effective different disinfectants are on killing any one microbe.

2 chemical control agents

1. gasses
2. liquids

2 gas control agents

1. sterilization
2. disinfection

3 liquid control agents

1. antisepsis
2. disinfection
3. sterilization

3 methods of mechanical control

1. sanitation
2. degermination
3. filtration sterilization

2 types of filtration sterlization

1. air
2. liquids

2 physical control agents

1. heat
2. raditation

2 types of radiation control agents

1. ionizing
2. non ionizing

2 types of heat control

1. dry
2. moist

ionizing radiation

uses x-rays and gamma rays to sterilize

Destroys bacterial endospores

not always effective against viruses

How does ionizing radiation work?

strips electrons from atoms

Penetrates deep into objects

Causes damage to DNA and potentially to plasma membrane

Also indirect damage by producing reactive molecules

what two byproducts does ionizing radiation produce?

1. Superoxide free radicals
2. hydroxyl free radicals

nonionizing radiation

uses UV rays to disinfect

Damages DNA causing thymine dimers

Generates free radicals

2 forms of dry heat control

1. incineration
2. dry oven

2 types of moist heat control

1. sterilization (steam under pressure)
2. disinfection (boiling water, hot water, pasteurization)

2 physical removal agents

1. surficants
2. soaps and detergents

surficant

breaks water surface tension

detergent

Emulsifies all hydrophobic lipids and fats so that you can physically remove the microbes from hands.

Ignatz Semmelweis

"savior of mothers"

The guy who figured out that washing hands is so important. Austrian surgeon in late 1800s. Delivered babies too. Before we had gloves they would go and do dissections of cadavers between giving birth. Friend of his got stuck with a scalpel and died and noticed that he died of what the pregnant women died of.

Figured out that if you wash your hands and instruments in a harsh chlorine bath (undiluted) then his patients survived. He became head of hospital and insisted everyone did this. Old surgical stink guys (see few slides later) did not like this and got offended by this saying I am a gentleman, I am clean. But he showed them the data.

Joseph Lister

He wore to surgery:
“an old blue frock-coat for operation, which he had previously worn in the dissecting room; stiff and glazed with blood”

Developed the first spray disinfectant: Carbolic Acid - phenol - will dissolve your skin. We do not use it anymore.

4 methods using heat and moisture

1. autoclave - true sterilization
2. canning
3. pasteurization
4. boiling

Pressurized steam

Autoclave used to sterilize using pressurized steam

use saturated steam under pressure to reach temperatures above boiling

Autoclave achieves sterilization at ___°C and ___psi in ____minutes

121
15
15

Pasteurization

Why developed?
What is it?
Does it sterilize?
What is it used for with our food?

Pasteur developed to avoid spoilage of wine

Controlled heating at temperatures well below boiling

Does not sterilize but significantly reduces organisms

Used to increase shelf life of food

flash pasteurization

What is it used for?

(High temperature short-term – HTST)

72°C for 15 seconds then rapid cooling (milk)

82°C for 20 seconds (ice cream)

ultra high temperature pasteurization

What is it used for?

(UHT) sterilization

140 to 150°C for 1 to 3 seconds

Used for single serving cream containers and boxed juices

The problem is that the higher the temp, the more likely you are to break down the chemical components of that food and alter the taste

dry heat

Not as effective as moist heat

Sterilization requires longer times and higher temperatures

200°C for 1.5 hours vs. 121°C for 15 minutes

oxidizes cell constituents and denatures proteins

Incineration

Oxidizes cell to ashes

Used to destroy medical waste and animal carcasses

Flaming laboratory inoculation loop incinerates organism

radiation

electromagnetic radiation

Energy released from waves

Shorter wavelength, higher frequency = more energy

Range of wavelengths is electromagnetic spectrum

Radiation can be ionizing or non-ionizing

Why is UV radiation limited to surface sterilization?

Limited to surface sterilization because UV radiation does not penetrate glass, dirt films, and other substances

irradiation

99.9-99.99% effective against E. coli on leafy greens

Breaks down cell walls a bit though

Meats, poultry, some shellfish and spices are also approved

#1 way to sterilize plastics

ionizing radiation is used for sterilizing what?

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

nonionizing radiation is used for what?

Used to destroy microbes in air, drinking water and surfaces

main sterilizing gas

Ethylene Oxide

How does sterilizing gas work?

Destroys microbes including endospores and viruses

Combines with and inactivates proteins

What is sterilizing gas used to sterilize?

Used to sterilize heat- or moisture- sensitive materials

what is the down side to using sterilizing gas?

Mutagenic and potentially carcinogenic

Extensive aeration of sterilized materials necessary

What are the vital targets for chemical microbial killing? (5)

1. Proteins (enzymes) - target its function, denature
2. Ribosomes - target its function
3. DNA - mutate it
4. Plasma membrane - poke holes in it, lysis
5. Cell wall - poke holes in it

3 main chemical methods of killing

1. disruption of plasma membrane
2. protein denaturation
3. oxidation

carbolic acid

Phenol

First used by Lister ca. 1870

disruption of plasma membrane

How do phenols work?

Act by denaturing proteins and disrupting cell membranes

effective in presence of organic material and long lasting

Kill most vegetative cells (5-10% kill Mycobacterium)

Not reliable against all viruses

Things that poke holes in membranes and trigger cell lysis are things that contain phenol in them. Effective against most bacteria but not mycobacterium and spores. But lots of disinfectants have phenol type compounds in them. It can poke holes in plasma membranes and can poke holes in membranes of our cells.

Examples of phenols

lysol
triclosan

4 main types of protein denaturation

1. alcohols
2. phenolics
3. heavy metals
4. quaternary ammonia

How does alcohol work as a chemical method of killing microbes?

Solutions of 60% - 80% isopropyl or ethyl alcohol kill vegetative bacteria and fungi. effective against mycobacteria.

Not effective against endospores and some naked viruses

Coagulates proteins and essential enzymes and damages lipid membranes

Commonly used as antiseptic and disinfectant

2 limitations to using alcohol as a chemical method of killing microbes

1. Evaporates quickly, limiting contact time
2. May damage material such as rubber and some plastics

How do heavy metals work as a chemical method of killing microbes?

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

Compounds combine with enzymes and proteins interfering with function

High concentrations of many metals toxic to human tissue

Silver still used as a disinfectant

Creams containing silver sulfadiazine used to prevent secondary infections

Also available on bandages for wound care

How does ammonia work as a chemical method of killing microbes?

It denatures proteins. Common in hospitals as detergent and denaturant. Pseudomonas bacteria causes infections in burn patients and in contact lens wearers. This bacteria has developed resistance against ammonia compounds.

2 main types of oxidation used in chemical microbial killing

1. halogens (iodine and chlorine)
2. hydrogen peroxide

How does hydrogen peroxide function as a chemical microbial killing agent?

Powerful oxidizing agent

Effectiveness depends on surface being treated

Living tissue produces catalase enzyme which breaks down hydrogen peroxide

More effective on inanimate objects

Useful as disinfectant

Leaves no residue

Doesn’t damage most materials

Hot solutions commonly used in food industry

Vapor-phase is more effective and can be used as sterilant

Readily biodegradable

oxidation

transfers electrons from one to another to break down physical components

How halogens work at killing microbes

Oxidize proteins and other cell components

tincture

alcoholic solution

idophore

carrier molecule

How is iodine used as a chemical microbial killer?

Kills vegetative cells but not reliable with endospores

Used as a skin antiseptic in tincture or iodophore

effective with mycobacteria

How is chlorine used as a chemical microbial killer?

Important disinfectant

Works through oxidation

Used to disinfect water supplies and swimming pools, dairy and food industries

Effective household disinfectant

Caustic to skin and mucous membranes

Destroys vegetative bacteria and fungi, but not spores

Can react with organic matter to form carcinogenic compounds

8 points to consider in choosing a chemical microbial killer

1. Highly effective - Fast acting, even when dilute, have a broad range of activity over various environmental conditions, soluble and active in both water and oils

2. Activity in presence of organic material - Many germicides inactivated in presence of organic matter

3. Toxicity

4. Compatibility with material being treated - Liquids cannot be used on electrical equipment

5. Residue - Residues neither toxic or corrosive, odorless, non-staining

6. Cost and availability

7. Storage

8. Environmental risk