Chapter 13: Control of Microbial Growth (Talia)

CFU

Colony forming units (instead of bacteria/cells) CFU per area (surface) CFU per mL (liquid)

Freezing vs. Refrigeration

Freezing reserves but does not reliably kill pathogens. Just slows growth. Refrigeration slows microbe growth, but not as much as freezing. Temps are between 0°C and 7°C. Freezing below -2°C may stop microbial growth and even kill susceptible organisms. Bacterial cultures and medical specimens requiring long-term storage or transport are often frozen at ultra-low temperatures of −70 °C or lower.

Asceptic Techniques

• Any procedures that minimize contaminating a patient. Method or protocol designed to prevent microbial contamination of sterile objects, locations, or tissues. • Ex: Using sterile equipment and sterilizing or disposing of contaminated equipment properly. Involves a combination of protocols that collectively maintain sterility, or *asepsis*, thus preventing contamination of the patient with microbes and infectious agents. Failure to practice aseptic technique during many types of clinical procedures may introduce microbes to the patient's body and put the patient at risk for *sepsis*, a systemic inflammatory response to an infection that results in high fever, increased heart and respiratory rates, shock, and, possibly, death.

Disinfection vs. Sanitization

• Both reduce numbers of microbes on fomites. • *Neither destroy endospores, so they do not accomplish sterilization*. • Disinfection requires longer exposure of the fomite to chemicals. Sanitization requires shorter exposure, but still meets public health standards. Sanitization is usually talking about maybe a minute or less of wiping down a surface. Disinfection can lower microbes even more and they usually ask you to let it sit for at least 15 minutes.

Listeria monocytogenes

• There is one important exception. Listeria monocytogenes is a psychrophilic bacterium that grows well at cold temperatures. • Susceptible foods include dairy products and lunch meats. • Preservatives help control its growth, but heating foods until they steam or avoiding susceptible foods is safest.

Pasteurization

• Uses heat but does not render the food sterile. Kills pathogens and reduces the number or spoilage-causing microbes while maintaining food quality. • Uses high heat at brief exposures to kill pathogenic and spoilage microbes. • Used for milk, dairy products, juice, and sometimes eggs and honey. • "Raw" milk, juice, honey that has not been treated should not be given to young children or anyone who is immunocompromised. Milk is shot through thin, little, heated tubes. The exposure is incredibly brief. Modern pasteurization is incredibly brief exposure, really old fashioned pasteurization is a much longer exposure to a lower temperature. Refrigeration simply slows down the growth of pathogens.

-cidal vs -static

-cidal refers to killing -static refers to inhibition -cidal chemicals kill microbes. Ex. A fungicidal chemical would kill a fungi. -static inhibit microbial growth. Ex. A bacteriostatic chemical would slow microbial growth. Food preservative chemicals are -static.

Desiccation (drying or dehydration)

A centuries old *preservation* technique. Works because all cells, including microbes, require water for their metabolism and survival. Although drying controls microbial growth, it might not kill all microbes or their endospores, which may start to regrow when conditions are more favorable and water content is restored.

Disk-Diffusion Method

A disk-diffusion assay is used to determine the effectiveness of chemical agents against a particular microbe. (a) A plate is inoculated with various antimicrobial discs. The zone of inhibition around each disc indicates how effective that antimicrobial is against the particular species being tested. Involves applying different chemicals to separate, sterile filter paper disks. The disks are then placed on an agar plate that has been inoculated with the targeted bacterium and the chemicals diffuse out of the disks into the agar where the bacteria have been inoculated. As the "lawn" of bacteria grows, zones of inhibition of microbial growth are observed as clear areas around the disks. Although there are other factors that contribute to the sizes of zones of inhibition (e.g., whether the agent is water soluble and able to diffuse in the agar), larger zones typically correlate to increased inhibition effectiveness of the chemical agent. The diameter across each zone is measured in millimeters.

noncritical

A medical item that comes into contact with intact skin and does not penetrate sterile tissues or come into contact with mucous membranes is called a(n) ________ item.

Amphyl

A phenol that is tuberculocidal. Kills Mycrobacterium tuberculosis.

Supercritical Fluid Sterilization

A pressurization technique used to sterilize tissues for transplant. *Yes, you can sterilize tissues for transplant.*

Disinfection

A process that inactivates most microbes on the surface of a fomite by using antimicrobial chemicals or heat. Because some microbes remain, the disinfected item is not considered sterile. Application examples: Cleaning surfaces like laboratory benches, clinical surfaces, bathrooms. Agents: Chlorine bleach, phenols (e.g. Lysol).

Tincture

A solution of an antiseptic compound dissolved in alcohol.

Autoclave

A specialized device for sterilizing materials with pressurized steam before use or disposal. Used to raise temperatures above the boiling point of water to sterilize items such as surgical equipment from vegetative cells, viruses, and especially endospores, which are known to survive boiling temperatures, without damaging the items. Rely on moist-heat sterilization.

BSL-1

Agents that generally do not cause infections in healthy humans. Few precautions are necessary.

Air Filtration

Air is commonly filtered through *High-Efficiency Particulate Air (HEPA) filters*. HEPA filters have effective pore sizes of 0.3 μm, small enough to capture bacterial cells, endospores, and many viruses, as air passes through these filters, nearly sterilizing the air on the other side of the filter. These are available for residential or commercial use. Ex: vacuum cleaners, A/C filters, air purifiers. *Yes, you could sterilize with this method.* You can combine HEPA filters with UVC light.

Phenols

Also known as a carbolic acid. First used by Joseph Lister to prep surgical instruments. A skin irritant. Less common in consumer products now. Triclosan is a hospital-grade disinfectant that should be reserved for hospital environments. *Disinfect*.

Disinfectants

Antimicrobial chemicals applied to a fomite during disinfection that *may be toxic to tissues*. Ideally, ________________ should be fast acting, stable, easy to prepare, inexpensive, and easy to use. An example of a natural disinfectant is vinegar; its acidity kills most microbes. Chemical disinfectants, such as chlorine bleach or products containing chlorine, are used to clean nonliving surfaces such as laboratory benches, clinical surfaces, and bathroom sinks.

Antiseptics

Antimicrobial chemicals safe for use on living skin or tissues. Examples include hydrogen peroxide and isopropyl alcohol. In addition to the characteristics of a good disinfectant, antiseptics must also be selectively effective against microorganisms and able to penetrate tissue deeply without causing tissue damage.

Fomites

Any non-living object that may be contaminated with microbes. Metals tend to not carry too many fomites.

Sonication

Application of ultrasound waves causes rapid changes in pressure within the intracellular liquid; this leads to *cavitation*, the formation of bubbles inside the cell, which can disrupt cell structures and eventually cause the cell to lyse or collapse. Useful in the laboratory for efficiently lysing cells to release their contents for further research; outside the laboratory, it is used for cleaning surgical instruments, lenses, and a variety of other objects such as coins, tools, and musical instruments. *Dental practices.* *Sterilization depends on the time, just as nonionizing radiation is time dependent for sterilization.*

B

Bleach is an example of which group of chemicals used for disinfection? a. heavy metals b. halogens c. quats d. bisbiguanides

Dry Heat Sterilization

Bunsen burner flame or Bacti-Cinerator. Not to be used on plastics.

Sterilants

Chemicals that can be used to achieve sterilization. Effectively kill all microbes and viruses, and, with appropriate exposure time, can also kill endospores.

Phenolics

Class of chemical disinfectants and antiseptics characterized by a phenol group that denatures proteins and disrupts membranes. Phenolics tend to be stable, persistent on surfaces, and less toxic than phenol. They inhibit microbial growth by denaturing proteins and disrupting membranes.

Zones of Inhibition

Clear areas that result on Disk Diffusion from inhibition of microbe growth by chemicals. Also seen when evaluating antibiotic effectiveness. When evaluating zones of inhibition, the *larger* the zone diameter, the more *effective* that chemical/antibiotic is against the microbe. If there is no zone around a disk, then that means that bacterium is *resistant*. *Remember, it is the pathogen that becomes resistant, not the patient!*

Nonionizing Radiation

Commonly used for disinfection and uses less energy than ionizing radiation. Does not penetrate cells or packaging. Ultraviolet (UV) light is one example; it causes thymine dimers to form between adjacent thymines within a single strand of DNA. When DNA polymerase encounters the thymine dimer, it does not always incorporate the appropriate complementary nucleotides (two adenines), and this leads to formation of mutations that can ultimately kill microorganisms. • Short wavelength ultraviolet light is antimicrobial. Look for "UV-C" or 260 nm lamps. • Creates pyrimidine (thymine) dimers in DNA, which distort DNA's shape resulting in mutations when DNA is transcribed into mRNA or replicated. • Drawback: less effective on liquids or growth media

Hand sanitizers, used to make tinctures.

Describe several specific applications of alcohols used in disinfectant products.

Quats (Quaternary Ammonium Salts)

Detergents that disrupt plasma membrane so they can actually kill microbes. Named for the characteristic quaternary nitrogen atom that confers the positive charge They are stable, nontoxic, inexpensive, colorless, odorless, and tasteless. They tend to be bactericidal by disrupting membranes. They are also active against fungi, protozoans, and enveloped viruses, but endospores are unaffected. In clinical settings, they may be used as antiseptics or to disinfect surfaces. *Disinfect or sanitize.* Mixtures of quats are also commonly found in household cleaners and disinfectants, including many current formulations of Lysol brand products, which contain benzalkonium chlorides as the active ingredients. Benzalkonium chlorides, along with the quat cetylpyrimidine chloride, are also found in products such as skin antiseptics, oral rinses, and mouthwashes.

Microbial Death Curve

Displays the logarithmic decline of living microbes exposed to a method of microbial control.

Boiling as a Sterilization Method

Does not destroy endospores, so it does not reliably sterilize. (Always use a pressure cooker if you home jar or can foods. Most case of botulism in the U.S. result from improper canning or jarring). Boiling is one of the oldest methods of moist-heat control of microbes, and it is typically quite effective at killing vegetative cells and some viruses. However, boiling is less effective at killing endospores; some endospores are able to survive up to 20 hours of boiling. Additionally, boiling may be less effective at higher altitudes, where the boiling point of water is lower and the boiling time needed to kill microbes is therefore longer. For these reasons, boiling is not considered a useful sterilization technique in the laboratory or clinical setting.

Copper, nickel, zinc

Doorknobs and other surfaces in clinical settings are often coated with ________, ________, or ________ to prevent the transmission of microbes.

Alkylating Agents

Effectively sterilize materials at low temperatures but are carcinogenic and may also irritate tissue. *Glutaraldehyde* and *o-phthalaldehyde *are used as hospital disinfectants but not as antiseptics. *Formaldehyde* is used for the storage of tissue specimens, as an embalming fluid, and in vaccine preparation to inactivate infectious agents. *Ethylene oxide* is a gas sterilant that can permeate heat-sensitive packaged materials, but it is also explosive and carcinogenic. The strongest of these are sterilants and will kill endospores. They are highly toxic and you won't find them at your local store.

High-Temperature Short-Time (HTST) Pasteurization

Exposes milk to a temperature of 72°C for 15 seconds, which lowers bacterial numbers while preserving the quality of the milk.

Biological Safety Levels (BSLs)

For researchers or laboratory personnel working with pathogens, the risks associated with specific pathogens determine the levels of cleanliness and control required. There are 4 levels: I, II, III, and IV. The BSL is determined by the agent's infectivity, ease of transmission, and potential disease severity, as well as the type of work being done with the agent.

Lyophilization

Freeze drying. Remove water before freezing. Combines cold exposure and desiccation for the long-term storage of foods and laboratory materials, but microbes remain and can be rehydrated.

Surfactants

Have hydrophilic heads that bind water & hydrophobic tails that bind dirt. Water then washes dirt containing microbes away. Surface-active agents, are a group of chemical compounds that lower the surface tension of water. Soaps are salts of long-chain fatty acids and have both polar and nonpolar regions, allowing them to interact with polar and nonpolar regions in other molecules. They can interact with nonpolar oils and grease to create emulsions in water, loosening and lifting away dirt and microbes from surfaces and skin. Soaps do not kill or inhibit microbial growth and so are not considered antiseptics or disinfectants. However, proper use of soaps mechanically carries away microorganisms, effectively degerming a surface. *Major component of soaps and detergents.* *Disinfect or sanitize ??? Ask Cori*.

BSL-3

Have the potential to cause lethal infections by inhalation. These may be either indigenous or "exotic," meaning that they are derived from a foreign location, and include pathogens such as Mycobacterium tuberculosis, Bacillus anthracis, West Nile virus, and human immunodeficiency virus (HIV). Labs require restricted access. Wear a respirator.

Sugar and Salt for Food Preservation

High sugar or salt content will also preserve foods by dehydrating microbes in the foods. These foods are hypertonic. Many microorganisms do not survive these conditions of high osmotic pressure. Honey, for example, is 80% sucrose, an environment in which very few microorganisms are capable of growing, thereby eliminating the need for refrigeration. Salted meats and fish, like ham and cod, respectively, were critically important foods before the age of refrigeration. Fruits were preserved by adding sugar, making jams and jellies. However, certain microbes, such as molds and yeasts, tend to be more tolerant of desiccation and high osmotic pressures, and, thus, may still contaminate these types of foods.

Nonionizing is commonly used for disinfection and ionizing is used for sterilization. Nonionizing does not penetrate cells or packaging. With nonionizing, yes, you could ultimately sterilize as well but with longer exposure times.

How does the effectiveness of ionizing radiation compare with that of nonionizing radiation?

Greater

If a chemical disinfectant is more effective than phenol, then its phenol coefficient would be ________ than 1.0.

High-level

If used for extended periods of time, ________ germicides may lead to sterility.

The air in the chamber is removed and replaced with increasing amounts of steam trapped within the chamber, resulting in increased interior pressure and temperatures above the boiling point of water.

In an autoclave, how are temperatures above boiling achieved?

Steam

In an autoclave, the application of pressure to ________ is increased to allow the steam to achieve temperatures above the boiling point of water.

Susceptibility or sensitivity

In the disk-diffusion assay, a large zone of inhibition around a disk to which a chemical disinfectant has been applied indicates ________ of the test microbe to the chemical disinfectant.

BSL-2

Include agents that pose moderate risk to laboratory workers and the community, and are typically "indigenous," meaning that they are commonly found in that geographical area. These include bacteria such as Staphylococcus aureus and Salmonella spp., and viruses like hepatitis, mumps, and measles viruses. Lab coat, gloves, face shield, autoclave.

Ionizing Radiation

Includes X-rays, gamma rays, and high-energy electron beams. Damage DNA, RNA, and proteins. Result: fatal mutations or cell death May directly cause DNA mutations to occur, or mutations may be introduced when the cell attempts to repair the DNA damage. As these mutations accumulate, they eventually lead to cell death. Used to treat lab plastics, medical supplies, and some foods. Ionizing is more dangerous than nonionizing.

Halogens

Including chlorine, fluorine, and iodine. Commonly used for disinfection. Chlorine compounds, including sodium hypochlorite, chloramines, and chlorine dioxide, are commonly used for water disinfection. Iodine, in both tincture and iodophor forms, is an effective antiseptic. Betadine is a solution of the iodophor povidone-iodine, and is a common skin antiseptic. *Disinfect*.

Heavy Metals

Kill microbes by binding to proteins, thus inhibiting enzymatic activity. They are *oligodynamic*, meaning that very small concentrations show significant antimicrobial activity. Ions of heavy metals bind to sulfur-containing amino acids strongly and bioaccumulate within cells, allowing these metals to reach high localized concentrations. This causes proteins to denature. • Copper sulfate is used to control algae in fountains. • Zinc oxide is used in diaper rash ointments. *Disinfect*.

Commercial Sterilization

Kills disease-causing microbes, but not microbes that grow at high-temps. Uses heat at a temperature low enough to preserve food quality but high enough to destroy common pathogens responsible for food poisoning, such as C. botulinum. • Doesn't achieve true sterilization. • Intended to kill Clostridium botulinum endospores to prevent botulism poisoning. • In the U.S., botulism poisoning is usually associated with improper home canning/jarring/brewing. Dates must be put on cans to reflect the fact that the commercial sterilization methods they use do not kill all microbes. Cans are sterilized but then they can be left open before they are sealed.

Thermal Death Time (TDT)

Length of time needed to kill all microorganisms in a sample at a given temperature. These parameters are often used to describe sterilization procedures that use high heat, such as autoclaving.

-stat (or -static)

Methods of microbial control that does not kill organisms but, instead, stop their growth. IDentified by the suffix _____________.

Bactericidal and fungicidal, may also be viricidal for enveloped viruses only. Inhibit the processes of sporulation and germination. Inexpensive and quite effective for disinfection of a broad range of vegetative microbes.

Name at least 3 advantages of alcohols as disinfectants.

-cide (or -cidal)

Physical and chemical methods of microbial control that kill the targeted microorganism are identified by the suffix ____________.

Radiation

Radiation in various forms, from high-energy radiation to sunlight, can be used to kill microbes or inhibit their growth.

Sterilization

Removal of all microbes. The complete removal or killing of all vegetative cells, endospores, and viruses from the targeted item or environment.

Degerming

Removes microbes by scrubbing. *Scrubbing, high-pressure sprays, friction of any kind.* Washing with ordinary soap, bathing, a dishwasher, or a washing machine are all examples of degerming. Remove most (but not all) mircrobes from the skin's surface.

Asepsis

Sterile state resulting from proper use of microbial control protocols. Treatments that reduce microbe #'s on living tissue (handwashing, surgical prep, bathing, mouthwash, applying Neosporin). Aseptic technique is more in reference to the lab.

Peroxygens

Strong oxidizing agents that can be used as disinfectants or antiseptics. Damage cellular molecules unless the microbe has catalase.

Sepsis

Systemic inflammatory response to an infection that results in high fever and edema, causing organ damage and possibly leading to shock and death.

True

T or F: Ionizing radiation can penetrate surfaces, but nonionizing radiation cannot.

True

T or F: Mercury-based compounds have fallen out of favor for use as preservatives and antiseptics.

False

T or F: Moist-heat sterilization protocols require the use of higher temperatures for longer periods of time than do dry-heat sterilization protocols do.

False

T or F: Sanitization leaves an object free of microbes.

False

T or F: Soaps are classified as disinfectants.

Bisguanides

The Hibiclens used in lab for hand washing, disrupts membranes and is static and cidal against a wide variety of microbes. *Disinfect or santize*.

Sanitization

The cleansing of fomites to remove enough microbes to achieve levels deemed safe for public health through application of heat or microbial chemicals. Application examples: Commercial dishwashing, cleaning public restrooms. Agents: Detergents containing phosphates (e.g. Finish), industrial-strength cleaners.

C

The decimal reduction time refers to the amount of time it takes to which of the following? a. reduce a microbial population by 10% b. reduce a microbial population by 0.1% c. reduce a microbial population by 90% d. completely eliminate a microbial population

Commercial Sterilization

The goal of ________ ________ protocols is to rid canned produce of Clostridium botulinum endospores.

Thermal Death Point (TDP)

The lowest temperature at which all microorganisms are killed in a 10-minute exposure.

Ultra-High Temperature (UHT) Pasteurization

The milk is exposed to a temperature of 138°C for 2 or more seconds. UHT pasteurized milk can be stored for a long time in sealed containers without being refrigerated; however, the high temperatures alter the proteins in the milk, causing slight changes in the taste and smell. Still, this method of pasteurization is advantageous in regions where access to refrigeration is limited. Can be stored for up to 90 days without refrigeration in airtight containers.

Antisepsis

The process of applying an antiseptic. Reduces microbial load on skin or tissue through application of a microbial chemical.

Decimal Reduction Time (DRT or D-value)

The time it takes for a protocol to yield a 1-log (90%) reduction in microbial population.

Water Activity

The water content of foods and materials. Can be lowered without physical drying by the addition of solutes such as salts or sugars. At very high concentrations of salts or sugars, the amount of available water in microbial cells is reduced dramatically because water will be drawn from an area of low solute concentration (inside the cell) to an area of high solute concentration (outside the cell).

BSL-4

These agents are the most dangerous and often fatal. These microbes are typically exotic, are easily transmitted by inhalation, and cause infections for which there are no treatments or vaccinations. Examples include Ebola virus and Marburg virus, both of which cause hemorrhagic fevers, and smallpox virus. There are only a small number of laboratories in the United States and around the world appropriately equipped to work with these agents.

Moist Heat Sterilization

Typically the more effective sterilization protocol because it penetrates cells better than dry heat does. Autoclaves use high pressure steam to sterilize. Autoclaves are capable of destroying everything with one notable exception: *Prions*.

Membrane Filtration

Used to filter liquids. To remove bacteria or eukaryotes, the filter pores must be 0.2 micrometers or smaller. Filtration is ideal for liquids that would be destroyed by heat. Provided that you use a filter with small enough pores, you could filter out prokaryotes, eukaryotes and larger viruses but do not rely on it for sterilization.

Chemical Preservatives

Used to inhibit microbial growth and minimize spoilage in some foods. •Hypothesized to inhibit microbial enzymes. •Generally considered safe in foods and consumer products. Commonly used chemical preservatives include sorbic acid, benzoic acid, and propionic acid, and their more soluble salts potassium sorbate, sodium benzoate, and calcium propionate, all of which are used to control the growth of molds in acidic foods. Each of these preservatives is nontoxic and readily metabolized by humans. They are also flavorless, so they do not compromise the flavor of the foods they preserve.

Alkylating agents and supercritical fluid.

What are the two sterilizing agents?

Can be used to kill microbes or inhibit their growth. Easily penetrate plastic and paper and can therefore be used to sterilize many packaged materials.

What are two advantages of ionizing radiation as a sterilization method?

An antiseptic is safe to use on living tissue whereas a disinfectant is not.

What is the difference between a disinfectant and an antiseptic?

Sterilization is the removal of all microbes and asceptic technique is a method used to prevent microbial contamination of sterile objects, locations, or tissues.

What is the difference between sterilization and aseptic technique?

According to the US Department of Agriculture (USDA), the only safe ways that frozen foods can be thawed are in the refrigerator, immersed in cold water changed every 30 minutes, or in the microwave, keeping the food at temperatures not conducive for bacterial growth.

What is the only safe way to thaw food?

B

Which biosafety level is appropriate for research with microbes or infectious agents that pose moderate risk to laboratory workers and the community, and are typically indigenous? a. BSL-1 b. BSL-2 c. BSL-3 d. BSL-4

Sterilization because it is the complete removal of all microbes, degerming and sanitization simply reduce the microbial load.

Which is most effective at removing microbes from a product: sanitization, degerming, or sterilization?

D

Which of the following best describes a microbial control protocol that inhibits the growth of molds and yeast? a. bacteriostatic b. fungicidal c. bactericidal d. fungistatic

B

Which of the following chemical food preservatives is used in the wine industry but may cause asthmatic reactions in some individuals? a. nitrites b. sulfites c. propionic acid d. benzoic acid

B

Which of the following is suitable for use on tissues for microbial control to prevent infection? a. disinfectant b. antiseptic c. sterilant d. water

D

Which of the following methods brings about cell lysis due to cavitation induced by rapid localized pressure changes? a. microwaving b. gamma irradiation c. ultraviolet radiation d. sonication

A

Which of the following microbial control methods does not actually kill microbes or inhibit their growth but instead removes them physically from samples? a. filtration b. desiccation c. lyophilization d. nonionizing radiation

A

Which of the following peroxygens is widely used as a household disinfectant, is inexpensive, and breaks down into water and oxygen gas? a. hydrogen peroxide b. peracetic acid c. benzoyl peroxide d. ozone

B

Which of the following refers to a disinfecting chemical dissolved in alcohol? a. iodophor b. tincture c. phenolic d. peroxygen

C

Which of the following terms is used to describe the time required to kill all of the microbes within a sample at a given temperature? a. D-value b. thermal death point c. thermal death time d. decimal reduction time

A

Which of the following types of medical items requires sterilization? a. needles b. bed linens c. respiratory masks d. blood pressure cuffs

Heavy metals are not selectively toxic to microbial cells. They may bioaccumulate in human or animal cells, as well, and excessive concentrations can have toxic effects on humans.

Why are many heavy metals both antimicrobial and toxic to humans?

Because soaps do not kill or inhibit microbial growth. They do however, carry microorganisms away, effectively degerming a surface.

Why are soaps not considered disinfectants?

It is less effective at killing endospores (could take up to 20 hours), less effective at high altitudes.

Why is boiling not used at a sterilization method in a clinical setting?

Alcohols

Work by rapidly denaturing proteins, which inhibits cell metabolism, and by disrupting membranes, which leads to cell lysis. Once denatured, the proteins may potentially refold if enough water is present in the solution. Alcohols are typically used at concentrations of about 70% aqueous solution and, in fact, *work better in aqueous solutions than 100% alcohol solutions*. This is because alcohols coagulate proteins. In higher alcohol concentrations, rapid coagulation of surface proteins prevents effective penetration of cells. The most commonly used alcohols for disinfection are ethyl alcohol (ethanol) and isopropyl alcohol (isopropanol, rubbing alcohol) Used in hand sanitizers and "rubbing" alcohol. *Disinfect*.