Micro Chapter 7

Form of chlorine: Chloramines

A combination of chlorine and ammonia. Used as a sanitizer and for disinfection in municipal water systems.

What are the advantages and disadvantages of using an autoclave?

Advantages: Preferred method of sterilization. Disadvantages: Cannot use if material can be damaged by heat or moisture. Steam under pressure fails to sterilize when the air is not completely exhausted.

What is decimal reduction time and why may it be useful?

(D value) is the length of time, in minutes, required to kill 90% of the population of bacteria at a given temperature.

What is betadine and why is it useful? When is it used?

(providone iodine) A surface active iodophor that improves the wetting action and serves as a reservoir of free iodine. Skin disinfection and wound treatment.

What is triclosan and why is it important?

A bisphenol, an ingredient in antibacterial soaps and at least one toothpaste. It is so widespread that resistant bacteria have been reported. Inhibits an enzyme needed for the biosynthesis of fatty acids.

What is hexachlorophene and why is it important?

A bisphenol, an ingredient of a prescription lotion, pHisoHEx, used for surgical and hospital microbial control procdures. Used to control some infections in nurseries.

What is the disk-diffusion method? When might it be used?

A disk of filter paper is soaked in a chemical agent, which is placed on an inoculated surface of an agar plate. A clear zone around the disk indicates inhibition; Used in teaching lab to evaluate the efficacy of a chemical agent.

What is plasma sterilization and why is it used?

A method available for the difficult task of sterilizing surgical devices with small interior diameters. Destroy endospores at low temperatures.

What is the use-dilution test? When might it be used?

A series of tubes containing increasing concentrations of the test disinfectants is inoculated and incubated; testing the effectiveness of antimicrobial agents against endospores, mycobacteria that causes tuberculosis, viruses, and fungi, because they are difficult to control with chemicals.

Sterilant

A sterilizing agent (heat)

What are the advantages and disadvantages of using triclosan?

Advantages: Effective against gram-positive bacteria but also works well against yeasts and gram-negative bacteria. Disadvantages: It is now widespread and resistant bacteria have been reported to certain antibiotics.

What are the advantages and disadvantages of using high pressure to control microbes?

Advantages: High pressure applied to liquid suspensions such as fruit juices can kill vegetative bacterial cells while preserving flavors, colors, and nutrient values. Disadvantages: Endospores are relatively resistant.

What are the advantages and disadvantages of using phenolics as disinfectants?

Advantages: Remain active in the presence of organic compounds, are stable, and persist for long periods after application. Disadvantages: Injure lipid containing plasma membranes.

What are advantages and disadvantages of using alcohols to control microbial growth?

Advantages: acting and then evaporating rapidly and leaving no residue. Disadvantage: Alcohols are unsatisfactory antiseptics when applied to wound. They cause coagulation of a layer of protein under which bacteria continue to grow.

List the major cellular and molecular targets used by control agents to kill or inhibit microbes.

Alteration of membrane permeability and damage to proteins and nucleic acids.

What is an antiseptic? How does it differ from a disinfectant?

Antisepsis is the chemical disinfection of living tissue, antiseptic is the chemical. Disinfectant treats surfaces or substances.

What are surfactants? List some examples.

Can decrease surface tension among molecules of a liquid. Soaps and detergents.

What are chlorhexidine and alexidine? What are the advantages and disadvantages of using them?

Chlorhexidine is a biguanide, used for microbial control on skin and mucous membranes. Alexidine is a similar biguanide and is more rapid in its action than chlorhexidine. Advantages: used for surgical hand scrubs and preoperative skin preparation in patients.

What is supercritical sterilization and when might it be used?

Combines chemical and physical methods. It has properties of both liquid and gas. Used for decontamination of foods and medical implants.

When is ethanol an effective antiseptic?

Concentrations of 70% but can be 60%-95%

When is isopropanol an effective antiseptic and disinfectant?

Concentrations of 70% but can be 60%-95%

What is disinfection?

Control directed at destroying harmful microorganisms.

How does UV light kill microbes? What are the advantages and disadvantages of using UV light to control microbes?

Damages the DNA of exposed cells by causing bonds to form between adjacent pyrimidine bases, usually thymines, in DNA chains. Advantages: Use to disinfect vaccines and other medical products. Disadvantages: The radiation is not very penetrating, so the organisms to be killed must be directly exposed to the rays. UV light can damage human eyes and prolonged exposure can cause burns and skin cancer in humans.

When is hydrogen peroxide used to control microbial growth? What are advantages and disadvantages of using it? Can it sterilize?

Disinfects inanimate objects. Medicine cabinets and in hospital supply rooms . Advantages: Food industry is increasing its use of hydrogen peroxide for aseptic packaging. Disadvantages: It is quickly broken down to water and gaseous oxygen by the action of the enzyme catalase which is present in human cells. YES

Which microbes are biguanides effective against? Which ones can they not control?

Effective against gram-positive and gram-negative bacteria, enveloped viruses. Not against pseudomonads.

How does chlorine in its various forms control microbial growth?

Either in gas or chemical combination.

What is the relationship between change in temperature and change in time for heat-based sterilization methods?

Equivalent treatments: as the temperature is increased, much less times is needed to kill the same number of microbes.

List at least two chemical sterilizers and state under what circumstances they are used.

Ethylene Oxide: Depends on alkylation, which leads to a cross-linking of nucleic acids and proteins. Chlorine dioxide: Use in water treatment prior to chlorination, where its purpose is to remove or reduce the formation of certain carcinogenic compounds sometimes formed in the chlorination of water.

Ignoring endospores, why are gram-negative bacteria more resistant to chemical biocides than gram-positive bacteria?

External lipopolysaccharide layer of gram-negative bacteria. Porins and mycobacteria.

List two forms of dry heat sterilization. What are the advantages & disadvantages of each one?

Flaming (incineration): Advantages- efficient for limited purposes. Hot-air sterilization: Disadvantages- requires higher temperatures and longer times to ensure sterilization.

Name at least one aldehyde and state why aldehydes can be useful in controlling microbial growth.

Formaldehyde. They inactivate proteins by forming covalent cross-links with several organic functional groups on proteins.

Define sepsis.

From the greek for decay or putrid. Indicates bacterial contamination, as in septic tanks for sewage treatment.

List two forms of ionizing radiation used to control microbes.

Gamma rays and X rays.

Why might sterilization time increase when using an autoclave?

Heat requires extra time to reach the center of the solid materials, such as canned meats, because such materials do not develop the efficient heat-distributing convection currents that occur in liquids. Heating large containers also requires extra time.

List all the physical methods of microbial control that you can think of.

Heat, filtration, low temperature, high pressure, desiccation, osmotic pressure and radiation.

Describe methods of controlling microbial growth using osmotic pressure.

High concentrations of these substances create hypertonic environment that causes water to leave the microbial cell. Preservation by desiccation. Both these methods deny the cell the moisture it needs for growth.

How does iodine control microbial growth? When is it used?

Impairs protein synthesis and alters cell membranes, by forming complexes with amino acids and unsaturated fatty acids. Used for skin disinfection and wound treatment.

What is desiccation and why is it used? When is it useful and when is it not useful?

In the absence of water. Mircoorganims cannot grow or reproduce but can remain viable for years. Used in hospital settings. Not useful for viruses and bacterial endospores.

What does the suffix "stat or stasis" mean? What is bacterostasis?

Indicates only that the substance inhibits. To stop or to steady.

What methods are being used to destroy prions on inanimate objects?

Infected animal carcasses are incinerated. Combined use of sodium hydroxide and autoclaving at 134 C. Addition of protease enzymes to the cleaning solution.

Name some halogens that are effective in controlling microbial growth.

Iodine and chlorine.

Form of Chlorine: Chlorine dioxide

Is a gas used for area disinfection, most notably to kill endospores of anthrax bacteria. And surface disinfectant

Form of Chlorine: Sodium dichloroisocyanurate

Is a water disinfectant issued by the US military.

What is peracetic acid and can it sterilize?

Is one of the most effective liquid chemical sporicides available. For washing fruits and vegetables and it is used to disinfect medical equipment. YES

What is thermal death point and why is it important?

Is the lowest temperature required to kill a liquid culture of a certain species of bacteria in 10 minutes.

Form of chlorine: Calcium Hypochlorite.

Is used to disinfect utensils.

Why are ethanol and isopropanol used with other chemical agents?

It enhances the effectiveness.

Form of Chlorine: Hypochlorous acid.

It is a strong oxidizing agent that inhibits enzymatic function.

Why is it a bad idea to use aluminum foil when sterilizing with an autoclave?

It is impervious to steam and should not be used to wrap dry materials that are to be sterilized because the steam would not contact it.

What effect does ionizing radiation have on microbes? When is it used?

Kills microorganisms, carry high energy and break DNA strands. Food preservation, sterilize pharmaceuticals and disposable dental and medical supplies and certain classes of mail.

What is a germicide? What does the suffix "-cide" mean?

Kills microorganisms. Indicates the killer of a specified organism.

Which situations might require sterilization? Which ones would not and why?

Liquids and Gases. Surgical wounds, a drinking glass or a fork, the body can cope with a few microbes

What is pasteurization? When is it used? Why is it used?

Mild heating that is sufficient to kill particular spoilage or disease organisms without seriously damaging the taste of the product.

What is ultra-high temperature pasteurization? When is it used?

Milk can be sterilized and stored without refrigeration. Coffee creamers.

What kind of sterilization method is used when one uses an autoclave?

Moist heat sterilization and pasteurization.

What are the three heat-based methods of controlling microbial growth?

Moist heat sterilization, pasteurization and dry heat sterilization.

Which microbes grow more easily in low moisture or high osmotic pressure environments?

Molds and yeasts.

What is the listing of microorganisms in descending order of resistance to chemical biocides? Why are they placed in this particular order?

More resistant: Prions, endospores of bacteria, mycobacterium, cysts of protozoa, vegetative protozoa, gram-negative bacteria, fungi including most fungal spores, viruses without envelopes, gram-positive bacteria, viruses with lipid envelopes./ Many biocides tend to be more effective against gram-positive bacteria, than against gram-negative bacteria.

What are quats? What are the advantages and disadvantages of using them?

Most effective against gram-positive bacteria, less so against gram-negative bacteria. Advantages: Are fungicidal, amebicidal, and virucidal against enveloped viruses. Disadvantages: They do not kill endospores or mycobacteria.

Are low temperatures sterilizing?

NO

Are microbial control methods uniformly effective against all microbes?

NO

What is a problem when deciding on using one disinfectant?

No single disinfectant is appropriate for all circumstances.

Why are heavy metals sometimes useful as antimicrobial agents?

Oligodynamic Action: a silver coin on an incoluated nutrient medium will inhibit growth for some distance.

List all the different kinds of disinfectants that you can think of.

Phenol and Phenolics, Bisphenols, Biguanides, Halogens, Alcohols, Heavy metals and their compounds, surface-active agents, Quaternary Ammonium Compouds, Chemical foods preservatives, antibiotics, aldehydes, chemical sterilization, plasmas, supercritical fluids, peroxygens and other forms of oxygen.

When may heavy metals be used to control microbes? What are some examples? Why do they work?

Plastic food containers infused with silver nanoparticles, which are intended to keep food fresher, and silver infused athletic shirts and socks, which are claimed to minimize odors. Mercury controls mildew in paints. Copper is used to destroy green algae that grow in reservoirs, stock ponds, swimming pools and fish tanks. Hand-sanitizer. Zinc: Weathered roofs of buildings down-slope from zinc-coated fittings. Mouthwashes and shampoos.

How do alcohols control microbial growth?

Protein denaturation, but can also disrupt membranes and dissolve many lipids.

What factors are important when deciding on which disinfectant to use?

Read the label, consider the nature of the material being disinfected. Whether the disinfectant will easily make contact with the microbes.

If washing with soap and water does not kill microbes, why is it used?

Reduces them

Which heavy metals are used to control microbes?

Silver, Mercury, copper and zinc.

What effects do low temperatures have on microorganisms?

Slows the metabolic rate of microbes

What effects do freezing have on bacteria?

Some can still grow.

What are some examples of chemical food preservatives and how do they control microbial growth?

Sorbic acid: inhibits mold spoilage in foods such as cheese. Benzoic Acid: an antifungal used in soft drinks and other acidic foods. Calcium propionate: prevents mold growth in bread. Inhibit enzymatic or metabolic activity. Sodium nitrate and nitrite: added to meats to produce a red color and to inhibit outgrowth of botulism endospores.

What happens if air is not exhausted during the autoclaving process?

Steam under pressure fails to sterilize.

Define asepsis.

The absence of significant contamination.

How could microwaves control microbial growth?

The heat of the microwave will kill most vegetative pathogens.

What is thermal death time and why is it important?

The length of time required to kill all bacteria in a liquid culture at a given temperature.

What factors influence the rate of antimicrobial treatments?

The number of microbes, environmental influences, time of exposure, microbial characteristics.

What is sanitization? When it usually used?

The reduction of microbial populations on objects to safe public health levels. Restaurant glassware, china, and tableware.

What is degerming? How does it differ from disinfection? From sterilization?

The removal of transient microbes from skin by mechanical cleansing or by an antiseptic. Disinfection destroys harmful microbes. Sterilization destroys all living microbes.

Sterilization

The removal or destruction of all living microoorganisms.

What is a disinfectant?

The use of a chemical (disinfectant) to treat an inert surface or substance.

When is filtration used? What kinds of filters may be used?

To sterilize heat-sensitive materials, such as some culture media, enzymes, vaccines, and antibiotic solutions. High-efficiency particulate air filters and membrane filters.

List all the different chemical methods of microbial control that you can think of.

Use-Dilution Tests and The Disk-Diffusion Method.

What is high-temperature short-time pasteurization? When is it used?

Uses temperatures of at least 72C for about 15 seconds to pasteurize milk. lowers total bacterial counts.

What are the conditions needed for sterilization when using an autoclave?

Vessels in which high steam pressures can be contained. Temperatures above that of boiling water.

If a population of bacteria dies at a constant rate of 90% per minute, what does that mean if the population starts at 1 million.

We are now left with 100,000 microbes.

Give two examples of popularly used quats.

Zephiran and Cepacol.

Why are nitrites used to preserve some foods?

added to meats to produce a red color and to inhibit outgrowth of botulism endospores. Prevent the germination and growth of any botulism endospores that might be present.

Form of chlorine: Sodium Hypochlorite

household bleach