Chapter 5: Control of Microbial Growth

What is sanitzation?

Generally implies a process that substantially reduces the microbial population to meet accepted health standards that minimize the spread of disease. Most people expect a sanitized object to look clean. This term does not indicate any specific level of control.

What is the most common and reliable method used to kill microbes?

Heat treatment; but it can alter the flavor and appearance of the products.

What is Cryptosporidium parvum?

A pathogen that causes diarrhea, that can survive traditional infection procedures. Water treatment regulations now require facilities to minimize the level of both DBPs and C. parvum in treated water.

What are the classes of germicidal chemicals?

Alcohols, aldehydes, biguanide, ethylene oxide, halogens, ozone, peroxygens, phenolic compounds, and quaternary ammonium compounds.

What are membrane filters?

Also called microfilmers, they have microscopic pores that allow liquid to flow through while trapping particles too large to pass; filters of 0.2 micrometers are used to remove bacteria (thin)

What is Ozone?

An unstable form of oxygen, is a powerful oxidizing agent; decomposes quickly and must be generate on-site by passing air or 02 between two electrodes. Ozone is used as an alternative to chlorine for disinfecting drinking water and wastewater.

What does alcohol do for microbial growth?

Aqueos solutions of 60-80% ethyl or isopropyl alcohol quickly kill vegetative bacteria and fungi; do not destroy bacterial endospores and some enveloped viruses. Alcohol denatures essential proteins such as enzymes and damages lipid membranes; proteins are more soluble and denature more easily in alcohol mixed with water; used as antiseptics to clear skin before injections that break skin; also used as disinfectants for treating instruments; evaporates quickly, limiting contact time.

What does biguanides do for microbial growth?

Chlorhexidine is the most effective of this group, extensively used in antiseptic products; stays on skin and mucous membranes, is of relatively low toxicity, and destroys a wide range of microbes, including vegetative bacteria, fungi, and some enveloped viruses.

What does halogens do for microbial growth?

Chlorine is used as a disinfectant, 1:100 dilution of household bleach effective; very low levels disinfect drinking water, Cryptosporidium oocysts, Giardia cysts survive. Chlorine dioxide used as disinfectant and sterilant; Iodine is used as iodophore, Iodine slowly released from carrier molecule, Pseudomonas species can survive in stock solution

What can interfere with heat penetration and the action of chemical disinfectants?

Dirt, grease, and body fluids such as blood; this is a reason why it is important to thoroughly clean items before disinfection or sterilization.

Why is selecting an effective antimicrobial procedure complicated?

Every procedure is complicated but the fact that every procedure has disadvantages that limit its use; an ideal, multipurpose, non-toxic method simply does not exist.

What are some environmental conditions that effect microorganisms? (5.2)

Factors such as pH and presence of organic materials influence microbial death rates.

What are peroxygens?

Hydrogen peroxide and peracetic acid are powerful oxidizing agents that can be used as sterilants under controlled conditions; readily biodegradable and are less toxic than the traditional alternatives (ethylene oxide and glutaradehyde. Hydrogen peroxide has aerobic cells that produce enzyme catalase (aerobic metabolism), more effective on inanimate objects, vapor-phase can be used as sterilant. Peracetic acid is effective on organic material

What does dry heat do to microorganisms? (5.3)

Incineration burns cell components to ashes. Temperatures achieved in hot air ovens destroy cell components and irreversibly denature proteins.

What is incineration?

It burns the cell components to ashes. In microbiology laboratories, the wire loops continually reused to transfer bacterial cultures are sterilized by flaming--heating them in a flame until they are red hot.

How long does it take for heat or chemicals to kill microbial population?

It depends on the number of cells present; it takes more time to kill a large population that it does to kill a small population, because only a fraction of organisms die during a given time interval.

What does low-temperature storage do for microbial growth?

Low temperatures above freezing inhibit microbial growth. Freezing essentially stops all microbial growth.

How are medical instruments categorized based on antimicrobial procedure? (5.2)

Medical instruments are categorized as critical, semi-critical, and non-critical according to their risk of transmitting infectious agents.

What does reducing the available water do for microorganisms?

Salting and drying decreases the availability of water in food below the limits required for growth of most microbes; the high-solute environment causes plasmolysis, which damages microbial cells.

How much time does it take to kill microorganisms? (5.2)

The amount of time it takes for heat or chemicals to kill population of microorganisms is dictated in part by the number of cells initially present. Microbial death generally occurs at a constant rate.

What is pasteurization?

The brief heat treatment usually applied to food items that reduces the number of spoilage organisms and destroys pathogens without changing the characteristics of the product.

What is the D value? (5.2)

The decimal reduction time, the time it takes to kill 90% of a population of bacteria under specific conditions.

What is disinfection?

The elimination of most or all pathogens on or in a material. In practice, the term generally implies the used of antimicrobial chemicals. Unlike with sterilization, some viable microbes may still remain after disinfection.

What is preservation?

The process of delaying spoilage of perishable products. Storage conditions can be adjusted to slow microbial growth. For example, food stored in a refrigerator will take longer to spoil than food left in a pantry. Alternatively, chemical preservatives can be added to a product. These are bacteriostatic.

What is membrane filtration?

Used to determine the number of bacteria in a liquid medium, retains bacteria, while allowing the fluid to pass through; this same principle can be used to physically remove microbes from liquids or air.

What does sterile mean?

A sterile item is free of all viable microbes, including endospores and viruses. Note, however, the term sterile does not consider prions. These infectious protein particles are not destroyed by standard sterilization procedures.

What are some ways to describe antimicrobial agents and processes? (5.1)

A sterile item is free of viable microbes, including endospores and viruses. Disinfection is the elimination of most or all pathogens on or in a material. Antiseptics are antimicrobial chemicals non-toxic enough to be used on body tissue.

What does the commercial canning process use to destroy microorganisms and viruses?

An industrial-sized autoclave (called a retort). The canning process is designed to endure that endospores of Clostridium botulinum are destroyed. This is critical because surviving spores can germinate in canned foods such as vegetables and meats. The resulting vegetative cells can grow in low-acid anaerobic conditions and produce botulinum toxin, one of the most potent toxins known.

What are the types of highly resistant microbes?

Bacterial endospores, protozoan cysts and oocysts, mycobacterium species, pseudomonas species, and non-enveloped viruses.

What are some chemical preservatives? (5.6)

Benzoic, sorbic, and propionic acids are sometimes added to food to prevent microbial growth. Nitrate and nitrite are added to some foods to inhibit the germination of endospores and subsequent growth of Clostridium botulinum.

The Centers for Disease Control (CDC) and Prevention has established precaution guideline for laboratories working with microorganisms, what are they called?

Biosafety levels (BSL); they range from BSL-1 (for work with microbes not know to cause disease in healthy people) to BSL-4 (for work with deadly pathogens for which no vaccine or specific treat exists).

How does moist heat destroy microbes?

By irreversibly denaturing their proteins. Examples include boiling, pasteurization, and pressurized steam.

What are quaternary ammonium compounds (quats)

Cationic detergents (positively charged), low toxicity, disinfection of food preparation surfaces; charged hydrophilic and uncharged hydrophobic regions. Most household soups are anionic (negatively charged). Positive charges of quotes attracted to negative charges of cell surface, reacts with membrane, not effective on endospores, mycobacteria, non-enveloped viruses, Pseudomonas resists, can grow in solutions

How do you select the appropriate germicide?

Consider toxicity, activity in the presence of organic material, compatibility with the material being treated, residue, cost and availability, storage and stability, and environmental risk.

To guide the selection of germicidal procedures, medical instruments are categorized according to their risk for transmitting infectious agents. These categories are what?

Critical instruments, semi-critical instruments, and non-critical instruments and surfaces.

What are protozoan cysts and oocysts?

Cysts and oocysts are stages in the life cycle of certain intestinal protozoan pathogens such as Giardia lamblia and Cryptosporidium parvum. These disinfectant-resistant forms appear in the feces of infected animals, including humans, and can cause diarrheal disease if ingested. Unlike endospores, protozoan cysts and oocysts are easily destroyed by boiling.

What are disinfectants?

Disifectants are chemicals used for disinfecting inanimate objects. They are toxic to many forms of life and therefore biocides (bio meaning "life", and cida meaning "to kill"). As they typically target harmful microbes, they are often called germicides. Bactericides kill bacteria, fungicides kill fungi, and virucides inactivate viruses.

What must water treatment facilities do?

Ensure that drinking water is free of of pathogenic microbes; chlorine has traditionally been used to disinfect water, saving hundreds of thousands of lives by preventing the spread of waterborne illnesses such as cholera. Chlorine and other disinfectants can react with naturally occurring chemicals in the water to form disinfection by-products (DBPs).

How do you select the appropriate germicidal chemical? (5.5)

Factors that must be included in the selection of an appropriate germicidal chemical include toxicity, residue, activity in the presence of organic matter, compatibility with the material being treated, cost and availability, storage and stability, and ease of disposal.

What are some other methods used to remove or destroy microbes? (5.4)

Filtration; membrane filters and depth filters retain microorganisms while letting the suspending fluid pass through. High-efficiency particulate air (HEPA) filters remove nearly all microorganisms from air. Radiation; ionizing radiation destroys cells by damaging cell structures and producing reactive oxygen species. Ultraviolet light damages the structure and function of nucleic acids. Microwaves kill microorganisms by generating heat. High pressure; this is thought to destroy microorganisms by denaturing proteins and altering the permeability of the cell.

What are chemical preservatives?

Germicidal chemicals that can be used to preserve non-food items (food preservatives must be non-toxic for safe ingestion); Benzoic, sorbic, and propionic acids are weak organic acids sometimes added to bread, cheese, and juice to prevent microbial growth. Nitrate and its reduced form nitrite serve a dual purpose in processed meats; inhibit endospore germination and vegetative cell growth, shown to be carcinogenic, form nitrosamines.

Why consider toxicity?

Germicides are at least somewhat toxic to humans and the environment; the benefit of disinfecting or sterilizing an item or surface be weighed against the risk associated with using the chemical.

Why consider environmental risk?

Germicides that retain their antimicrobial activity after use can interfere with wastewater treatment systems; the activity of those germicides must be neutralized before disposal.

What is boiling?

Getting water to 100 degrees Celsius easily destroys most microorganisms and viruses. Drinking water that might be contaminated during floods or other emergency situations should be boiled for at least 5 minutes; not method of sterilization because endospores can survive.

Who was Joseph Lister?

He was a British physician who revolutionized surgery by introducing methods that prevent wounds from becoming infected. He was impressed by Pasteur's work of fermentations and caused by "minute organisms" and wondered if they were responsible for the pus that formed in infected wounds. He then experimented by applying carbolic acid, a toxic compound, directly onto damaged tissues and found it prevented infections. Carbolic acid would dressing became standard in practice and his patients no longer developed gangrene. He also helped with the germ theory of disease. Lister also improved his methods even further by using surgical procedures that excluded bacteria from wounds. These procedures included sterilizing instruments before use and maintaining a clean environment in the OR. The oral antiseptic Listerine was named after him in 1879 when it was introduced as a surgical antiseptic.

Why is minimizing the numbers of microbes in healthcare settings is particularly important?

Healthcare-associate infections (HAIs); patients in healthcare facilities, particularly hospitals, are often more susceptible to infectious agents because of their weakened condition. In addition, patients may undergo invasive procedures such as surgeries, cutting the intact skin that would otherwise help prevent infection. Finally, pathogens are more likely to be found in healthcare settings because of the high concentration of patients in their feces, urine, respiratory droplets, or other body secretions.

Why are some sterilization and disinfection procedures inappropriate for certain types of material?

Heat treatment can damage many types of plastics and other materials. Irradiation provides an alternative to heat, but the process damages some types of plastics. Moist heat (such as boiling water) and liquid chemical disinfectants cannot be used to treat moisture-sensitive material.

Why consider activity in the presence of organic material?

Hypochlorite (bleach) and many other germicides react with organic matter, losing their effectiveness in doing so. Chemicals such as phenolics tolerate the presence of some organic matter.

What does ethylene oxide do for microbial growth?

It is an extremely useful gaseous sterilizing agent that destroys all microbes, including endospores and viruses, by reacting with proteins. As a gas, it penetrates well into fabrics, equipment, and implantable devices such as pacemakers and artificial hips; useful for sterilizing heat- or moisture-sensitive items such as electrical equipment, pillows, and mattresses; many disposable laboratory items, including plastic Petri dishes and pipettes, are also sterilized with ethylene oxide; applied in a special chamber that resembles and autoclave; mutagenic and carcinogenic, increased malignancies in long-term users.

Why is heat treatment one of the most useful methods of microbial control?

It is reliable, safe, relatively fast and inexpensive, and does not introduce potentially toxic substances into materials. Some heat-based methods sterilized the product, whereas others decrease the number of microbes.

What consider compatibility with the material being treated?

Items such as electrical equipment often cannot withstand liquid chemical germicides, and so gaseous alternatives must be employed; corrosive germicides such as hypochlorite often damage metals and rubber.

How does drying food help with reducing microbial growth?

Lyophilization (freeze drying) is used for preserving foods such as coffee, milk, meats and vegetables; drying is often supplemented by salting; drying stops microbial growth but does not reliably kill, numerous causes of salmonellosis from dried eggs.

Why consider residue?

Many chemical germicides leave a toxic or corrosive residue; if such a germicide is used to treat an item, the residue must be removed by washing the item.

What are metal compounds?

Metal compounds kill microbes by combining with sulfhydryl groups of enzymes and other protein; high concentrations of most metals are too toxic to human tissue to be used medically. Silver is one of the few metals still used as a disinfectant.; doctors were required by law to add drops of another silver compound, 1% silver nitrate, into the eyes of newborns to prevent ophthalmia neonatorum caused by Neisseria gonorrhoeae. Compounds of mercury, tin, arsenic, copper, and other metals were once widely used as preservatives in industrial products and to prevent microbial growth in recirculation cooling water; extensive use resealed in serious pollution of natural waters, which is now strictly regulated.

What does moist heat do to microorganisms? (5.3)

Moist heat destroys microorganisms by causing irreversible coagulation of their proteins. Pasteurization utilizes a brief heat treatment to destroy spoilage and disease-causing organisms. Pressure cookers and autoclaves use pressurized steam to achieve temperatures that can kill endospores. The most important aspect of the commercial canning process is to ensure that endospores of Clostridium botulinum are destroyed.

Is dry heat as efficient as moist heat?

No, it does not penetrate microbes as well as moist heat, so it it is less efficient at killing them, and therefore requires longer times and higher temperatures. For example, 200 degree Celsius for 90 minutes of dry heat has the killing equivalent of 121 degrees Celsius for 15 minutes of moist heat.

How do you decide which antimicrobial procedure to use? (5.2)

One of the most critical considerations in selecting a method of destroying microorganisms and viruses is the type of microbial population thought to be present on or in the product.

Why are microorganisms in a biofilm more resistant to chemical disinfectants than their free-living counterparts?

Partly due to the protective nature of the accumulated extra polymeric substances, this means that materials that foster the development of biofilms should be scrubbed before being treated with a chemical disinfectant.

How do you use chemicals to destroy microorganisms and viruses? (5.5)

Potency of germicidal chemical formulations; germicides are grouped according to their potency as sterilants, high-level disinfectants, intermediate-level disinfectants, or low-level disinfectants.

How is pasteurization used?

Prevents spoilage of wine without changing the flavor; used to destroy heat-sensitive spoilage organisms in foods and beverages, increasing the product's shelf life without significantly altering its quality; widely used to destroy pathogens in milk and juices, protecting consumers from diseases such as tuberculosis, brucellosis, salmonellosis, and typhoid fever.

What is a relatively new concern for healthcare facilities?

Prions; fortunately, a disease caused by these agents is thought to be exceedingly rare--less than 1 case per 1 million persons per year. Healthcare facilities, however, must take special precautions when handling tissue that may be contaminated with prions, because these infectious particles are very difficult to destroy.

What is electromagnetic radiation?

Radio waves, microwaves, visible and ultraviolet (UV) light rays, and gamma rays are all examples; this form of energy travels in waves and has no mass; the amount of energy is related to the wavelength, which is the distance form crest to crest (trough to trough) of a wave.

What is decontamination?

Reduces the number of pathogens to a safe level. The treatment can be as simple as thorough washing, or it may involve the use of heat or disinfectants.

What is low-temperature storage?

Refrigeration inhibits growth of pathogens and spoilage organisms by slowing or stopping critical enzyme reactions; freezing preserves foods and other products by stopping all microbial growth, some microbial cells killed by ice crystal formation, but many survive and can grow once thawed

What is ultra high-temperature (UHT)?

Shelf stable boxed juices and milk, as well as single serving containers of half-cream served in restaurants are treated using this technique; this destroys all microorganisms that can grow under normal storage conditions. The UHT process for milk requires rapidly heating the milk to 140 degrees Celsius, holding it at that temperature for a few seconds and then cooling it.

Why consider cost and availability?

Sine germicides are less expensive and more readily available than others; hypochlorite can easily be purchased in the form of household bleach; ethylene oxide gas is not only expensive but requires a special chamber that effects cost and practicality.

What are some situational considerations for microbial growth? (5.1)

Situations encountered in daily life, hospitals, microbiology laboratories, food production facilities, water treatment facilities, and other industries warrant different degrees of microbial control.

What are the classes of germicidal chemicals? (5.5)

Solutions of 60-80% ethyl or isopropyl alcohol in water rapidly kill vegetative bacteria and fungi by coagulation enzymes and other essential proteins, and by damaging lipid membranes. Glutaral-dehyde, ortho-phthaladehyde and formaldehyde destroy microorganisms and viruses by inactivating proteins and nucleic acids. Chlorhexidine is a biguanide extensively used in antiseptic products. Ethylene oxide is a gaseous sterilizing agent that destroys microbes by reacting with proteins. Sodium hypochlorite (liquid bleach) is one of the least expensive and most readily available forms of chlorine. Chlorine dioxide is used as a sterilant and disinfectant, Iodophores are iodine-releasing compounds used as antiseptics. Metals interfere with protein function. Silver-containing compounds are used to prevent wound infections. Ozone is used was an alternative to chlorine in the disinfection of drinking water and wastewater. Peroxide and per acetic acid are both strong oxidizing agents that can be used alone or in combination as sterilants. Phenolics destroy cytoplasmic membranes and denature proteins. Quaternary ammonium compounds are cationic detergents; they are non-toxic enough to be used to disinfect food preparation surfaces.

Why consider storage and stability?

Some germicides are sold as concentrated stock solutions, decreasing the required storage space; the stocks are simply dilutes according to the manufacturers instructions before use; some have limited shelf life once prepared.

What does adding sugar to salt do for microorganisms?

Sugar and salt draw water out of cells, dehydrating them; food poisoning bacterium Staphylococcus aureus can grow in relatively high salt conditions.

How do you reduce the available water in microorganism?

Sugar and salt draw water out of cells, preventing the growth of microorganisms. Lyophilization is used for preserving food. The food is first frozen and then dried in a vacuum.

What influences the effectiveness of disinfection techniques on microbial death rates?

Temperature and pH; a solution of sodium hypochlorite (household bleach), can kill a suspension of M. tuberculosis at a temperature of 55 degrees Celsius in half the time it would take if the suspension were held at 50 degrees Celsius. The hypochlorite solution is even more effective at a low pH.

What does aldehydes do for microbial growth?

The aldehydes glutaraldehyde, oath-phthaladehyde (OPA), and formaldehyde destroy microorganism and viruses by forming chemical bonds that cross-link and inactivates proteins and nucleic acids A 2% solution of alkaline glutaraldehyde is one of the most widely used liquid chemical sterilants; formaldehyde is used as a gas or as formalin, an aqueous solution 37% solution; effective germicide that kills most microbes quickly; formalin is used to kill bacteria an inactivate viruses for use of vaccines.

What is the D value?

The decimal reduction time; the time required for killing 90% of a bacterial population under specific conditions. For example, if 90% of a bacterial population of 10,000 organisms is killed at a given temperature during the first 5 minutes, then 1,000 organisms remain. Approximately 90% of those organism will be killed in the next 5 minutes leaving 100, and so on; one D value reduces the number of cells by one order of magnitude (it would take 20 minutes, 4 D values to reduce a population of 10,000 to only one survivor.

What are bacterial endospores?

The endospores of Bacillus, Clostridium, and related genera are the most resistant form of life typically encountered. Only extreme heat or chemical treatment ensures their complete destruction.

What does commercially sterile mean?

The endospores of some thermophiles may survive. Theses are not usually a concern because they grow only at temperatures well above those of normal storage. The commercial canning process is designed to reduce a population of 10^12 C botulinum endospores to only one spore.

What are some approaches to control microbial growth? (5.1)

The methods used to destroy or remove microbes can be physical, such as heat treatment, irradiation, and filtration, or chemical.

What is irradiation?

The process of exposing food to radiation; used to destroy microbes and chemical additives to prevent their growth, but the risk of toxicity must always be a concern; The Food and Drug Administration (FDA) regulates these options.

What are some of the processes to control microorganisms?

The processes used to control microorganisms are either physical or chemical, or a combination of both. Physical methods include heat treatment, irradiation, filtration, and mechanical removal (washing).

What is sterilization?

The removal or destruction of all microorganisms and viruses on or in a product. Microbes can be removed by filtration or destroyed using heat, certain chemicals or irradiation. Destruction of microorganisms means they can not be "revived" to multiply even when they transfer from the sterilized product to an ideal growth medium.

What does the ultimate choice depends on then selecting an effective antimicrobial procedure?

The type and number of microbes to be controlled, environmental conditions, risk for infection, and the composition of the item to be treated.

What is aseptic technique?

The use of specific methods to prevent microorganism from contaminating an environment; although all microbiology laboratory personnel must use these measures, those who work with known pathogens must be more careful.

What are mycobacterium species?

The waxy cell walls of mycobacteria make them resistant to many chemical treatments. Because of this, stronger, more toxic chemicals must be used to disinfect environments that may contain mycobacterium tuberculosis.

What are non-critical instruments and surfaces?

These come into contact only with unbroken skin so they pose little risk for infection. Countertops, stethoscopes, and blood pressure cuffs are examples.

What are semi-critical instruments?

These come into contact with mucous membranes, but do not penetrate body tissue; they include gastrointestinal endoscopes and endotracheal tubes. They must be free of all viruses and vegetative bacteria. The few endospores that may remain pose little risk for infection because mucous membranes are effective barriers agains their entry into deeper tissue.

What are pseudomonas species?

These common environmental organisms are not only resistant to some disinfectants, but in some cases actually grow in them. Pseudomonas species can cause serious healthcare-associated infections.

What are intermediate-level disinfectants?

These destroy all vegetative bacteria, including mycobacteria, fungi, and most, but not all viruses; do not kill endospores even with prolonged exposure; used to disinfect noncritical instruments such as stethoscopes.

What are high-level disinfectants?

These destroy all viruses and vegetative microorganisms, but do not readily kill endospores; used to treat semi critical instruments such as gastrointestinal endscopes.

What are low-level disinfectants?

These destroy fungi, vegetative bacteria except mycobacteria, and enveloped viruses; do not kill endospores nor do they always destroy non-enveloped viruses; general purpose disinfectants

What are antiseptics?

They are antimicrobial chemicals non-toxic enough to be used on skin or other body tissue. These are routinely used to decrease bacterial numbers on skin before invasive procedures such as surgery.

How are potent germicidal chemical formulations grouped?

They are grouped according to their potency; sterilants, high-level disinfectants, intermediate-level disinfectants, low-level disinfectants

What are sterilants?

They can destroy all microbes including endospores and viruses; also called spores; destruction of endospores take 6-10 hours; used to treat heat-sensitive critical instruments (scalpels)

What are critical instruments?

They come in direct contact with body tissues; they include needles and scalpels and MUST be sterile.

How do microwaves effect microorganisms?

They do not effect them directly, but the heat they generate can be lethal; it is important to remember that they heat food unevenly, so even heat-sensitive cells can sometimes survive.

What are phenolic compounds (phenols)?

They have unpleasant odors and irritate the skin; phenolics kill most vegetative bacteria, Mycobacterium at high concentrations; wide activity range, reasonable cost, remain effective in presence of detergents and organic contaminates; considered non-toxic for skin applications, use cautioned by FDA and EPA, Triclosan and Hexachlorophene

What does bacteriostatic mean?

They inhibit the growth of bacteria but do not kill them.

What are high-efficiency particulate air (HEPA) filters?

They remove nearly all airborne particles 0.3 micrometer or larger. These filters are used for keeping microorganisms out of specialized hospital rooms designed for patients extremely susceptible to infection.

What do microbiology laboratories do as an approach of controlling microorganisms?

They routinely work with microbial cultures and consequently must use rigorous methods to control microorganism; to ensure that cultures remain pure, all media and instruments that contact the culture must first be sterilized to avoid contaminating the culture with environment microbes. All materials used to grow microorganisms must be treated before disposal to avoid contaminating workers and the environment.

What are depth filters?

They trap material within thick porous filtration material such cellulose fibers. They have complex passages that retain microorganism while letting the suspending fluid pass through the small holes.

What happened to patients undergoing surgery before the late 19th century?

They were at great risk of developing fatal infections, due to unsanitary medical practices and hospital conditions. Physicians did not know that their hands could pass diseases from one patient to the next, or that microscopic organisms could infect open wounds. Modern hospitals use strict procedures to avoid microbial contamination.

What is ionizing radiation?

This radiation has enough energy to remove electrons from atoms. This harms cells directly by destroying DNA and damaging cytoplasmic membranes; high energy gamma rays are used extensively to sterilize heat-sensitive materials, including medial equipment, disposable surgical supplies, and drugs such as penicillin. Gamma rays break DNA and RNA strands, killing the microbes but not changing the chemical composition; high energy gamma rays are approved for use on foods, although consumer resistance has limited uses; FDA has approved for spices and dried hers, fruits, vegetables, and grains (insect control), pork (parasite control), and poultry, beef, lamb, and pork (bacterial control).

What is the most important step in stopping the spread of many infectious diseases?

Thorough hand washing with soup and water; washing and scrubbing with soaps and detergents achieves routine control. Beneficial skin microbiota reside deeper on underlying layers of skin and hair follicles.

Why must food-processing facilities keep their surfaces relatively free of microorganisms?

To avoid contamination; if machinery used to grind meat is not cleaned properly, it can create an environment in which bacteria multiply, eventually large quantities of product.

Why must health facilities be especially careful to control microorganisms in the operating rooms?

To avoid infection; instruments used in invasive surgical procedures must be sterile to avoid introducing even normally harmless microbes into deep body tissue where they could easily cause infection.

What is ultraviolet radiation?

Ultraviolet light in wavelengths of approximately 220-300 nm destroys microbes by damaging their DNA. It penetrates poorly; cannot be used to destroy microbes in solid substances or turbid liquids; most effective when used at close range against exposed microorganisms; can damage skin and the eyes and promote the development of skin cancers.

What is filtration used for?

Used extensively to remove organisms from heat-sensitive fluids such as sugar solutions, beer, and wine.

What is high-temperature-short-time (HTST)?

Used in most pasteurization techniques; milk is heated at 72 degrees Celsius for 15 seconds, but the parameters must be adjusted for different products; ice cream is rich in fats so it is is pasteurized at 82 degrees Celsius for 20 seconds.

What is high pressure processing?

Used to decrease the number of microbes (pasteurization) in commercial food products without using high temperatures; destroys microbes by denaturing proteins and altering cell permeability; employs high pressure up to 130,000 psi; products keep their color and flavor associated with fresh foods.

How are heat and moisture tolerant items such as surgical instruments, most microbiological media, and reusable glassware sterilized?

Using autoclave; water in a chamber in the autoclave is heated to form steam, causing the pressure in the chamber to increase. The higher pressure, in turn, increases the temperature at which steam forms. Steam at atmospheric pressure never exceeds 100 degrees Celsius, but steam at an additional 15 psi (pounds per square inch) is 121 degrees Celsius, a temperature that kills even endospores. Typical conditions for sterilization is at 15 psi and 121 degrees Celsius in 15 minutes. To destroy prions, autoclaving takes place at 132 degrees Celsius for 1 hour is effective.

What are non-enveloped viruses?

Viruses such as poliovirus that lack a lipid envelope are more resistant to disinfectants. Conversely, enveloped viruses, such as HIV, tend to be very sensitive to these chemicals.

How do foods and other perishable products retain their quality longer?

When contaminating microbes are destroyed, removed, or inhibited.