What form of microbial life is the most difficult to destroy?

Define the term D value.

Would it be safe to say that if all bacterial endospores had been killed, then all other medically important organisms had also been killed?

-The endospores of Bacillus and Clostridium are by far the most resistant forms of life.

-The D-value is the time it takes to reduce the population by 90%

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Compare and contrast pasteurization, sterilization using pressurized steam, and the commerical canning process.

Pasteurization significantly decreases the number of heat-sensitive microorganisms, including spoilage microbes and pathogens (except sporeformers). Using high-temperature-short-time (72Cº 15 sec) method & Ultra-high-temperature method(140-150Cº for several sec).

Pressurized steam such as autoclavingheat water in an envlosed vessel that achieves temperatures above 100C and additional atmospheric pressure for 15 minutes. Endospores die at 121Cº.

Commercial cannin process uses pressurized steam in an industrial-sized autoclave called a retort.

Explain the drawbacks and benefits of using dry heat rather than moist heat to kill microorganisms.

-Dry heat is not as efficient as wet heat in killing microorganisms, requiring longer times and higher temperatures.

-But dry heat can be used to destroy medical wastes and contaminated animal carcasses.

Why is it important that the commercial canning process destroys the dendospores of Clostridium botulinum?

What are two purposes of pasteurization?

Would endospores be destroyed in the pasteurization process?

-Surviving spores can germinate and the resulting vegetative cells can grow in the anaerobic conditions of low-acid canned foods, producing botulinum toxins.

-Used to destroy spoilage organisms and kill pathogens.

-No because the porcess is not long enough to sterilize large volumes.

Describe how depth filters, membrane filters, and HEPA filters, are each used to remove microorganisms.

Depth filters - trap material within the thick filtration material such as cellulose fibers or diatomaceous earth.

Membrane filters - have microscopic pores that allow liquid to flow through while trapping particles that are too small to pass through the pores. A vacuum is used to help pull the liquid through the filter.

High-Efficiency-Particulate-Air filters - remove from air nearly all microorganisms that have a diameter greater than 0.3µm.

Describe how gamma irradiation, ultraviolet irradiation, and microwaves each destroy microorganisms.

Ionizing radiation - causes biological harm both directly, by destroying DNA and possibly damaging cytoplasmic membranes, and indirectly, by producing reactive molecules such as superoxide and hydroxyl free radicals.

Ultraviolet radiation - Non-ionizing radiation that destroys directly, by affecting the DNA molecules to form covalent bonds creating thymine dimers.

Microwaves - Microwaves do not affect microorganism directly but can kill microbes by the heat they generate in an item.

What is the difference between sterilants, high-level disinfectants, intermediate-level disinfectants, and low-level disinfectants.

Sterilants- can destroy all microorganisms, including their endospores and viruses. Treat heat-sensitve critical instruments such as scalpels.

High-level disinfectants - destroy all viruses and vegetative microorganisms, but they do not reliably kill endospores.

Intermediate-level disinfectants - destroy all vegetative bacteria including mycobacteria, fungi, and most, but not al viruses.

Low-level disinfectants - destroy fungi, vegetative bacteria except mycobacteria, and enveloped viruses.

Describe important factors to consider when selecting an appropriate germicidal chemical.

When selecting the appropriate germicidal chemical consider:

-Toxicity - risk of exposure

-Activity in the prescence of organic matter - inactivated by organic matter

-Compatibility with the material being treated - damage and tolerance of materials

-Residue - toxic or corrosive residue, thoroughly rinse with water

-Cost and availability - less expensive and readily available or expensive

-Storage and stability - limited shelf life

-Environmental risk - germicides must be neutralized before disposal into sewage treatment.

Compare and contrast the characteristics and use of alcohols, aldehydes, biguanides, ethylene oxide gas, halogens, metals, ozone, peroxygens, phenolic compounds, and quaternary ammonium compounds as germicidal chemicals.

Alcohol (ehanol and isopropanol) Easy to obtain and inexpensive. Rapid evaporation limits their contact time.

Aldehydes(glutaraldehyde and formaldehyde) Capable of destroying all forms of microbial life. Irritating to the respiratory tract, skin, and eyes.

Biguanides (chlorhexidine) Relatively low toxicity, destroys a wide range of microbes, adheres to and persits on skin and mucous membranes.

Ethylene Oxide Gas - Easily penetrates hard-to-reach places and fabrics and does not damage moisture-senstive material. It is toxic, explosive, and potentially carinogenic.

Halogens (chlorine and iodine) - Chlorine solutions are inexpensive and readily available; however, organic compounds and other impurities neutralize the activity. Some forms of chlorine may react with organic compounds to form toxic chlorinated products. Iodine is more expensive than chlorine and does not realiably kill endospores.

Metals (silver) - Most metal compounds are too toxic to be used medically.

Ozone - This unstable form of molecular oxygen readily breaks down.

Peroxygens (hydrogen peroxide adn peracetic acid) - Readily biodegradeable and less toxic than traditional alternatives. The effectiveness of hydrogen peroxide as an antiseptic is limited because th eenzyme catalase breakes it down. Peracetic acid is a more potent germicide than is hydrogen peroxide.

Phenolic Compounds (triclosan and hexachlorophene) - wide range of activity, reasonable cost, remains effective in the presence of detergents and organic contaminants, leaves an active antimicrobial residue.

Quaternary ammonium compounds (benzalkonium chloride and cetylpridinium chloride) - Non-toxic enough to be used on food preparation surfaces. Inactivated by anionic soaps and detergents.

Explain why it is essential to dilute iodophores properly.

Why would a heavy metal be a more serious pollutant than most organic compounds.

-Nosocomial infections can result if a Pseudomonas-contaminated iodophore is unknowingly used to disinfect instruments.

-Mecury, tin, arsenic, copper, and other metals result in serious pollution of natural waters if not controlled.

Explain how chemical preservatives, low-temperature storage, adding salt or sugar, and drying food can all be used to preserve perishable products.

Chemical preservatives are weak organic acids that are added to foods to alter cell membrane functions and interfere with energy transformation. They prevent the growth of bacteria and fungi.

Low-temperature storage - At low temperatures above freezing, many enzymatic reactions are very slow or nonexistant.

Adding salt or sugar- salting creates a high-solute environment which causes plasmolysis, and inhibits cell growth. Brine - salty water soaking.

Drying food- removing water by desiccating.

What organism that causes food poisoning is able to grow under high-salt conditions?

What is the risk of consuming nitrate- or nitrite-free cured meats?

Preservation by freezing is sometimes compared to drying. Why would this be so?

-Staphylococcus aureus

-Nitrates and nitrites can be converted to nitrosamines during hte frying of meats in hot oil or by metabolic activites of the intestinal bacteria. Nitrosamines have been shown to be potent carcinogens.

-Freezing essentially stops all microbial growth. The formation of ice crystals can irreversibly damage microbial cells, killing up to 50% of microorganisms.

What is the primary reason that milk is pasteurized?

To kil pathogens, and increase shelf life

What is the primary reason that wine is pasteurized?

To destroy spoilage organisms

What is the most chemically resistant non-spore forming bacterial pathogen?

Mycobacterium species, the waxy cell walls of mycobacterium make them resistant to many chemical treatments.

Why are low acid foods processed at higher temperatures than high acid foods?

Surviving spores can germinate and the resulting vegetative cells can grow in the anaerobic conditions of low-acid canned foods, such as vegetables and meats.

Explain why it takes longer to kill a population of 10⁹ cells than it does to kill a population of 10³ cells.

It takes more time to kil a large population than it does to kill a small population, because only a fraction of organisms die during a given time interval.

How is an iodophore different from a tincture of iodine?

A tincture contains the iodine dissolved in alcohol.

An iodophore links iodine to a carrier molecule that releases free (unbound) iodine slowly.

How does microwaving a food product kill bacteria?

Do not affect microorganisms directly but can kill microbes by the heat they generate in an item.

How is preservation different from pasteurization?

Preservation are added to prevent or slow the growth of microbes, but Pasteurization does not sterilize substances but significantly reduces the numbers of heat-sensitive organisms, including pathogens.

How are heat-sensitive liquids sterilized?

Filtration is used extensively to remove organism from heat-senstive liquids. Such as unpasteurized beer, sterilization of sugar solutions, and clarification of wine.

Name two products commonly sterilized using ethylene oxide gas.

As a gas it penetrates well into fabrics, equipment, and implatable devices. It is particularly useful for sterilizing heat- or moisture- sensitive items such as electrical equipment, pillows, and mattresses. Many disposable laboratry items, including plastic Petri dishes and pipets, are also sterilize with ethylene oxide.