MicroBio Exam III - Ch 11

Explain the mode of action of alcohols and their limitations as effective antimicrobials.

Alcohol's method of action typically will be contingent on the amount of its concentration. If its concentration exceeds 50% and higher it can upset cell surface tension, disintegrate membrane lipids, and eliminate overall membrane structure. Alcohol can allow higher microbial activity at 70% than 100% since water is still used. Alcohol does not kill bacterial endospores at a normal temperature that a room might have.

Distinguish among the terms sterilization, disinfection, antisepsis, and decontamination.

Among the four types of microbial control, only antisepsis involves solely living or animate surfaces. Antiseptics destroy or inhibit vegetative pathogens. Vegetative pathogens are less resistance than bacterial endospores. Hence, antiseptics agents could not destroy bacterial endospores. Decontamination is another microbial control method. Decontamination involves both animate and inanimate surfaces. Decontamination is the mechanical removal of most microorganisms from an animate or inanimate surface. The two subcategories of decontamination are sanitization and degermation. Disinfection is the destruction or removal of vegetative pathogens from inanimate surfaces. Like antiseptics, disinfection will not destroy all the microorganisms. The disinfection agents are physical processes or chemical agents. The chemical agent is called disinfectant. For example, bleach is a disinfectant. Disinfectant is usually toxic to human and animal tissues. Disinfection may not completely destroy or removal all microorganisms from the inanimate surface. Sterilization completely destroys or removes all living microorganisms. After sterilization, no microorganism exists. Sterilization is used on inanimate surfaces. Sterilizing agents are called sterilants. Sterilants are very strong. Sterilants could destroy the spores. Spores are the most resistant. Hence, sterilization destroys other less resistant microbes. There are four methods of microbial control. The four methods of microbial control are antiseptics, disinfection, decontamination, and sterilization. Antiseptic, disinfection, and decontamination remove most of the microbes. Only sterilization completely destroys and removes all microorganisms.

Identify advantages and disadvantages of cold treatment and desiccation.

Cold treatment is performing heavy refrigeration on microbes and this often slows activities of many microbes. However even though some are killed during this procedure they often do not destroy the harmful bacteria. This can lead to infections of Salmonella for example. Desiccation occurs when vegetative cells have water taken out of them. Some feeble pathogens are destroyed during this process but often many other types can survive this and even other kinds are put in a preservation state.

Explain two methods of dry heat control.

Dry heat is used to sterilize objects. Sterilize means to kill all the miroorganisms. The temperature of dry heat is higher than moist heat. The time the objects are exposed to dry heat is longer. Incineration and dry oven use dry heat. Incineration may use temperature of over 6,000 degree Celsius. The objects are exposed to intense dry heat. The heat will kill all microorganisms. The exposed microorganisms and other substances will be burned into ashes or turn into gases. Incineration is used to sterilize heat-resistant objects. In addition, incineration is used to destroy contaminated objects. Objects that could be sterilized or destroyed by incineration are heat-resistant glass, syringes, needles, dressings, and bandages. Dry oven uses less intense temperature than incineration. Dry oven is used when the objects could not be sterilized with moist heat. The objects are exposed to dry heat for about four hours. The temperature of the dry heat is about 200 degree Celsius. Objects that could be sterilized with dry oven are glassware, metallic instruments, powders, and oils. Incineration and dry oven use dry heat. The dry heat has a much higher temperature than moist heat. Dry heat is used when moist heat could not sterilized objects. In addition, dry heat is used to destroy contaminated objects.

Pinpoint the most appropriate applications of hydrogen peroxide agents.

Hydrogen peroxide is most appropriately used to sterilize medical equipment. These medical objects are complex, hard to clean, heat-resistant, delicate, and fragile. Hydrogen peroxide is also used as sterilant for heat-resistant, delicate, and fragile objects.

Differentiate between the two types of radiation control methods, providing an application of each.

Ionization method occurs when radiation shoots orbital electrons from an atom which lead to ions to be created. One example of ionizing radiation are gamma-ray machines that have radioactive cobalt and this is highly useful as an alternative for sterilizing materials that can be extremely subtle to heat or chemicals. Nonionizing radiation stimulates atoms by pushing them to a higher energy level but does not ionize them. One example is ultraviolet radiation.

Compare and contrast moist and dry heat methods of control, and identify multiple examples of each.

Moist heat can be created by boiling water, steam or very hot water. This usually functions at much lower temperatures and is uses times of very short exposure to get the same results as dry heat. Cellular structure can be destroyed during this process but the main effect of it is to denature proteins and help with coagulation of proteins. It also will stop any metabolism of the cell. In dry heat there is very low content of moisture. This can be done using a coil that is electric or by flame. It works by dehydration of the cell of interest and take out the water that is critical for metabolism of microbe. It also can denature proteins. Some examples of moist heat are boiling water which is pasteurization and disinfection. Some examples of dry heat are incinerations and hot-air oven.

Discuss several different halogen agents and their uses in microbial control.

One important halogen agent is chlorine. It has been very useful for hundreds of years. It has been used in antisepsis and disinfection. The major types of this agent are both gaseous and liquid. They are usually used in a massive scale for treating water, wastewater as well as sewage. Another useful halogen agent is iodine. It can break cells of microorganisms and also disrupt a microbes metabolism. It can also be used before surgery and on infections.

Identify examples of some heavy metal control agents and their most common applications.

Organic mercury tinctures like thimerosal and nitro-mersol are useful in the practice of antiseptics and infection avoidance. However, they cannot be used on skin that is broken because they can be injurious and stop healing. One example is nitrate solutions which are used in gonococcal infections in the baby's eyes. This disease occurs when they have been infected via their mother's birth canal during birth. They can also be used inside the mouth of dental issues.

Define the term surfactant, and explain this antimicrobial's mode of action.

Surfactants are compounds that can decrease the tension between a solid and a liquid. They can serve as detergent, foaming agents, emulsifiers as well as soaps. They typically have ends that are positively charged and they usually latch on well with the negative charge surfaces of the bacteria's proteins. The hydrocarbon chain of the surfactant will let the detergent to also destroy the cell membrane.

Name six methods of physical control of microorganisms.

The agents of the physical microbial control methods are heat, lyophilization, ionizing radiation, nonionizing radiation, filtration, and osmotic pressure. These agents target cellular structures and cellular processes. The damage of cellular structures and cellular processes could kill or inhibit the growth of microorganisms.

Name the desirable characteristics of chemical control agents.

The first criterion involves the effectiveness of the chemical agent in low concentration. A chemical meets the first criterion if it could kill microorganisms when the chemical is in low concentration. The second criterion involves the solubility of the chemical in water or alcohol. The chemical meets the second criterion if it could be dissolved in water or alcohol. The chemical must have long-term stability. The stability of the chemical facilitates long term storage. The third criterion involves broad-spectrum microbicidal action without being toxic to human and animal tissues. Broad-spectrum microbicidal action means that the chemicals could be used in varied amount to achieve varied targets. Hence, varied amount is used to achieve varied effectiveness. The third criterion also states that this chemical should not be toxic to human and animal tissues. The fourth criterion states that the antimicrobial chemical agent must be able to penetrate through inanimate surfaces and be able to sustain a cumulative or persistent action. This chemical should be able to pass through a barrier and reach the targeted destination. The fifth criterion states that an antimicrobial chemical agent must be resistant to becoming inactivated by organic matter. The sixth criterion states that an antimicrobial chemical agent should have noncorrosive or nonstaining properties. This chemical should not be corrosive to other substances. In addition, this chemical should not stain other substances. The seventh criterion states the chemical should have sanitizing and deodorizing properties. The seventh criterion does not require the chemical to have sterilizing effect. According to the eighth criterion, the chemical should be affordable and readily available. This chemical should be available as a natural resource or it should be available as a synthetic substance. Very few antimicrobial chemical agents meet all eight criteria.

Identify applications for ethylene oxide sterilization.

Ethylene oxide (ETO) is a gas at room temperature. It is an alkylating agent. Hence, it could react with the functional groups of DNA and proteins. The reaction disrupts DNA replication and enzymatic actions. Consequently, the affected microorganisms will die. Ethylene oxide (ETO) has many medical uses. ETO is used to sterilize and disinfect plastic materials and delicate instruments. ETO is also used to sterilized prepacketed medical devices, surgical supplies, syringes, and Petri dishes. Ethylene oxide (ETO) is also used as a disinfectant for food. People use ETO to disinfect sugar, spices, and dried food. Hence, ethylene oxide is an effective antimicrobial agent for organic and inorganic materials. Ethylene oxide is a good choice over heat or liquid chemicals. Many medical instrument and food are not heat resistant. In addition, disinfecting food in liquid would cause the food to change its favor and taste. In those circumstances, gas and vapor microbicidal agents are better alternative to heat and liquid chemicals. Ethylene oxide is a gas. Hence, Ethylene oxide is an effective microbicidal agent for delicate medical instrument and food.

Outline the process of filtration and describe its two advantages in microbial control.

Filtration typically works by using filters that are composed of microbes. They are typically made of very small membranes of polycarbonate, cellulose acetate, and different types of plastics. Typically they have small sizes of pores that are used to create the filters. Many are extremely precise and can have very tiny diameters that are often only a couple nanometers large. Ones with extremely small pores can even allow sterilization and filter out the unnecessary microbes like endospores. Filtration is often an excellent control because it can sterilize. For example, a sterile liquid filtrate can be done using this process.

Discuss the advantages and disadvantages of aldehyde agents in microbial control.

Glutaraldehyde is a very effective aldehyde agent that is commonly used for sterilization. Viruses typically are to be broken down even after tiny exposure times. Its main disadvantage is that it is somewhat unstable during high temperatures as well as high pH. Formaldehyde is a feasible intermediate disinfectant but is very toxic and can aggravate the skin and this puts a damper on its effectiveness.

Identify some common uses of osmotic pressure as a control method.

Osmotic pressure is used to control the growth of microorganisms. A hypertonic environment will cause the cells to lose water. Plasmolysis or shrinking of the cells will occur. Without the essential water, the cells could not grow and multiply. Adding particles could create hypertonic environment. Adding salt and sugar to food create hypertonic environment for the microorganisms. People use osmotic pressure to prevent microorganisms from growing and multiply in their food. Some uses of osmotic pressure are adding salt to meat and fish. Some people add sugar to jellies and fruits. People use osmotic pressure to preserve their foods. They want to prevent their food from spoilage.

List advantages and disadvantages to the use of phenolic compounds as control agents.

Phenols are used for general disinfection of cesspools, drains, and animal quarters. However they are not particularly good for germicide in medicine. This is because they can cause many effects that are irritating on humans. They do not interact well with matter that is organic although their detergent actions are quite helpful.

Identify the types of microorganisms that are most resistant and least resistant to control measures.

Prions and bacterial endospores have the highest resistance. These pathogens are not easily destroyed and removed. A method that could destroy prions and endospores could also destroy other less resistant microorganisms. Sterilization is likely to destroy and remove these pathogens. Protozoan cysts and some viruses are moderately resistant to the methods of microbial control. Hence, it is necessary to be selective in the use of microbial control. The following microorganisms have the least resistance to microbial control: most bacterial vegetative cells, fungal spores, hyphae, yeasts, and protozoan trophozoites. These types of microorganisms are the easiest to destroy and remove. Several methods of microbial control could destroy or remove these microorganisms while leaving the higher resistant microbes behind.

Compare the action of microbicidal and microbistatic agents, providing an example of each.

Static means to stand still while cidal means to kill. One type of static example is a bacteristatic agent that stops the growth of bacteria that occurs on tissues or on items in some environment. One example of cidal would be bactericide which is a chemical that kills bacteria except but does not kill any in the endospore stage.

Explain four different methods of moist heat control.

The four ways that use moist heat are steam under pressure, nonpressurized steam, pasteurization, and boiling water. An autoclave uses steam under pressure. The pressure of water is increased. The increase of pressure increases the temperature of the steam. The released steam is very hot. This highly pressurized steam could kill most if not all microorganisms. To achieve sterilization, it is necessary to increase the pressure. An autoclave is used to sterilized glassware, cloth, rubber, and heat-resistant plastics. Tyndallization is the process that uses nonpressurized steam. Without the added pressure, the temperature of the steam is not as high as the pressurized steam. Hence, multiple exposures with the nonpressurized steam are necessary to sterilize objects. Another term for tyndallization is intermittent sterilization. Intermittent sterilization is used to sterilize heat-sensitive culture media, and canned food. Pasteurization is a technique that is used to disinfect liquid or beverages. Basically, the liquid is boiled to pasteurize it. Pasteurization could not kill all microorganisms. However, pasteurization kills most microorganisms. These microorganisms may cause illnesses and food poisoning. Boiling water is another disinfection technique. The objects are placed in water. Heat is added until the water boiling. The water usually boils at 100 degree Celsius. This temperature is not high enough to kill all microorganisms. However, boiling water would kill many pathogens. Boiling water is used to disinfect drinking water, materials for babies, food preparation, utensils, bedding, and clothing. Moist heat is used in four ways. The four ways of using moist heat are steam under pressure, nonpressurized steam, pasteurization, and boiling water. The goal is to sterilize or disinfect objects. Steam under pressure and nonpressurized steam could sterilize objects. Pasteurization and boiling water could disinfect objects.

Name four categories of cellular targets for physical and chemical agents.

The physical and chemical agents have four categories of cellular targets. The four cellular targets are the cell wall, the cell membrane, cellular processes, and proteins.

Define thermal death time and thermal death point, and describe their role in proper sterilization.

Thermal death time is the smallest segment of required time to destroy every test microbes at a certain temperature. For example, the thermal death time is found for microbial species that are often prevalent in our lives. Thermal death point is the lowest temperature that is needed to destroy all microbes in a certain sample within ten minutes. The TDT for commercial canneries is 121degC for 30 minutes. This number indicates when food is okay to eat. Most vegetative cells die in 3 minutes to 60 minutes from 50 to 60 degrees Celsius. Endospores usually perish for boiling temperatures than exceed 20 minutes.