Chemical & Physical Methods of Microbial Control

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Differentiate between a disinfectant & antiseptic

*disinfection (sanitation) - reduces the number of pathogens to a level at which they pose no danger of disease; used on inanimate objects like bathroom surfaces, etc
*antiseptics - kill microbes or inhibit their growth on skin or other living tissue

Differentiate between microbiocidal & microbiostatic

-Microbiocidal - kills
-Microbiostatic - limits growth

Differentiate between sterilization and commercial sterilization

*Sterilization - destroy all microbial life (even all bacterial endospores and fangal spores)
*Commercial sterilization - food is subjected only to enough heat to destroy Clostridium botulinum spores; there are some thermophiles that are spore-producers and could spoil food, but do not cause human disease

What are 2 advantages to using heat to control microbes?

simple, inexpensive

What is the mode of action of heat?

Protein denaturation

What is a disadvantage to boiling?

Does not kill all endospores or thermophiles

What are the conditions for autoclaving? (include time, temp, pressure)

121 C, 15psi, for 15-20 min

What is the effect of pressure in autoclaving?

Increases temp above boiling

Can you think of a disadvantage to autoclaving?

Cannot use with heat sensitive materials

Which is more effective - boiling or autoclaving?

Autoclaving - it kills all endospores & thermophiles

What is an advantage of pasteurization?

Does not change the taste/appearance of food

When is it used?

Dairy products, wine, beer, egg beaters

What is the effect of using cold to control microbes?

Microbiostatic; does not sterilize

What is the mode of action of cold?

Slows down metabolic rate

As far as temperature goes, most disease-causing microbes are ______philes

meso - philes

The two types of radiation that kill bacteria are ________________&______________.

nonionizing (UV) and ionizing (X-rays, Gamma rays)

What is the mode of action of radiation?

Mutates DNA

What is it's effect?

sterilization

What are the disadvantages of using UV light?

Only kills on surfaces (doesn't penetrate) & can be harmful to humans

Name 2 types of ionizing radiation?

X-rays & Gamma rays (does not change taste of food)

What is the disadvantage to using this type of radiation?

Technically complex (need special equipment)

How is this type of radiation currently being used?

Meat, produce, grains, spices, poultry

Filtration is replacing pasteurization in some cases. Why?

Filtration causes even less damage to heat sensitive substances; used with media, antibiotics, beer

What are some microorganisms that can pass through a filter? Why?

Viruses, mycoplasma, spirochetes; Viruses are small, mycoplasma have no cell wall so they can squeeze through pores in filter, spirochetes corkscrew through pores

Another word for lyophilization is _________ _____________. In this process materials are frozen and then the ice is changed directly to a _________________.

freeze drying;
gas

What is an advantage to using this process over heat drying?

Avoids chemical changes caused by heat drying

What is the mode of action of lyophilization?

Slows down metabolic rate like freezing; also bacteria don't like dry environment

What is a disadvantage to this process?

expensive

What is the mode of action of using high concentrations of salt or sugar to control microbes?

Create hypertonic environment that "sucks" the water out of bacterial cells

Germicides are tested by comparing their effectiveness to _________, a traditional germicide.

phenol

Describe the paper disc method for testing germicides

Paper discs are saturated with the chemical agent and placed on the surface of an agar plate inoculated with a test organism. Clear "zones of inhibition" appear around the discs if the chemical agent is effective

The phenol coefficient of a germicide is 2. Which solution would be more effective (phenol or the germicide being tested)

the germicide being tested
(A disinfectant w/ a p.c. of 1.0 has the same effectiveness as phenol. Greater than 1 means it's more effective than phenol, less means it's not as effective)

Name the 2 test organisms traditionally used to test germicides

Staphylococcus aureus, Salmonella typhi

What are the disadvantages to using alcohols?

Evaporates quickly, doesn't kill endospores; not good for wound treatment (causes coagulation of proteins, producing a layer under which microbes grow)

Why is Staphylococcus relatively resistant to hydrogen peroxide?

It produces the enzyme catalase which breaks down hydrogen peroxide into water and oxygen; the bubbles you see is the oxygen

Explain the mode of action of surfactants

Penetrates oily substances in water & breaks them apart into small droplets that become coated with surfactant molecules. The hydrophobic end of the surfactant sticks into the droplets & the hydrophilic end is attracted to the water. The result is an emulsion, a fine suspension of oily droplets in water, which can now be rinsed away.

What is an advantage of using alkylating agents?

Sterilize

What's a disadvantage?

Carcinogenic to humans

What are the 2 factors that determine safe heat treatments for canning?

Heat and time

Name 2 chemical preservatives that are added to commercially prepared foods.

Sodium benzoate, sobic acid, sodium nitrate (& nitrite), calcium propionate

For many germicides, the higher the concentration, the more effective the germicide. This is not the case for what chemical? (a 70% solution is more effective than a 100% solution)

Alcohol

Why is chloramine considered more effective than chlorine for the disinfection of drinking water?

More stable than chlorine and does not react with organic materials

Why would an alcohol gel be preferred to antimicrobial soap for handwashing by health care professionals?

Works well in the presence of blood, no bacterial resistance, quicker to use, less drying than soap

_____a phenolic; common ingredient in household & hospital disinfectants; remains active in the presence of blood & feces

Lysol

______also known as gentian violet; blocks cell wall synthesis; inhibits G (+) bacteria & yeasts

Crystal Violet

______alkylating agent; used to preserve tissues & to embalm; low concentrations are used to inactivate microbes for vaccines

formalin

______a surfactant added to another chemical agent to help them penetrate fatty substances

wetting agent

_____a chlorinated phenolic; used in soaps & lotions (Physohex); now known to increase risk of brain damage in babies

hexachlorophene

______heavy metal; applied to newborn's eyes to prevent gonorrhea

silver nitrate

_____charged nanospheres of oil droplets; disrupt cell envelope

PCMX (nanotechnology)

______now used by water treatment facilities to disinfect drinking water

chloramines

______used as an antiseptic & disinfectant; bubbles when it comes into contact with tissue

hydrogen peroxide

______alkylating agent; gas; used to sterilize heat labile (heat sensitive) materials; toxic to humans

ethylene oxide

______an alcohol; widely used as skin antiseptics; a 50-70% solution in water is the most effective

ethanol

______heavy metal containing mercury; antiseptic; basic first aid kit supplies; contains thimerosal

merthiolate

______heavy metal containing mercury; antiseptic; "monkey blood"; now banned by FDA; now contain quats instead

mercurochrome

______heavy metal containing mercury; found in merthiolate; also used as a vaccine preservative and in cosmetics, nasal sprays, etc

thimerosal

______heavy metal used to treat fungal skin infections; included in dandruff shampoos

selenium sulfide

______heavy metal used as a fungicide on crops and produce; used as an algaecide and a molluscicide

copper sulfate

______a halogen; a mixture of iodine and surfactants; used for surgical scrubs and to disinfect skin before surgery

iodophor; betadine/isodine; povidone-iodine (PVP iodine)

______prevents germination of Clostridium botulinum spores in meats

sodium nitrate

______a halogen; household bleach; added to drinking water and swimming pools

chlorine (Chlorox)

______surfactants; wash away microbes, but do not kill them

soaps/detergents

______a halogen; a mixture of iodine & alcohol; used as an antiseptic

iodine tincture

______a phenolic from the greasewood bush used to prevent the rotting of wooden posts, fences, railroad ties, etc

cresol

______surfactant; widely used; effectiveness decreased in presence of soap; supports Pseudomonas growth

quats; zephiran/cepacol/bactine

______biguanide; used in mouthwashes, surgical hand scrubs skin creams, to treat gum disease (Peridex, Periogaurd, Periochip); interferes with vitamin K absorption; teeth staining occurs when taking iron

chlorhexidine

______phenol used in many antibacterial soaps and cutting boards

triclosan

What are the advantages to using PCMX, a product that uses nanotechnology?

Works as well as Quats and chlorine-based products, non-irritating, kills quickly, no toxic fumes, non flammable, noncorrosive, non-drying to skin, do harmful dermal effects, doesn't require EPA handling statements

Why is thimerosal used in vaccines?

Thimerosal contains mercury and is used in vaccines as a preservative.

Why is there concern over the use of thimerosal in vaccines?

There is public concern over a proposed link between mercury and autism

T or F Thimerosal has been removed from childhood vaccines

The FDA claims that thimerosal has been removed from childhood vaccines (DTAP, HepB, HepA, IPV, Hib, MMR etc). There are still a few manufacturers that use thimerosal during the manufacturing process and then the thimerosal is removed; technically there is a trace left in the vaccine, but the FDA says that these vaccines should be considered thimerosal free. The good thing is that there are thimerosal free alternatives to these vaccines, so you don't have to receive the ones that have the trace amt. There is still thimerosal in adult vaccines such as tetanus, diphtheria (single dose are thimerosal free)

If consumers are concerned about the use of thimerosal in vaccines, what kind of vaccines should they worry about and why?

Some multi-dose preps of vaccines may still contain thimerosal

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