Chapter 9
How are the modes of action of the two major antimicrobial drug classes categorized?
-Alteration of Cell Walls and Membranes-if the wall is disruped by physical or chemical agents, it no longer prevents the cell from bursting as water moves into the cell by osmosis. -Damage to Proteins and Nucleic Acids-when protein bonds are broken by extreme heat or certian chemicals, the proteins shape changes (Denaturing proteins cease to function) Chemicals, radiation, and heat can also alter and even destroy nucleic acids. The portion of a ribosome that actually catalyzes the sunthesis of proteins is called a ribosozyme and chemical agents that interfere with nucleic acids also stop protein sythesis
What does the suffix -cide or cidal indicate?
-cide or -cidal - agents or methods that destroy or permanently inactivate a particular type of microbe e.g. fungicides destroy fungal hyphae, spores, and yeasts.
What does the suffix -stasis or -static indicate?
-static or -stasis - Agents or techniques that inhibit the growth of microbes without necessarily killing them e.g. refrigeration is bacteriostatic
What major factors influence antimicrobial agent efficiency?
1)Site to be treated - e.g. human tissues cannot take harsh chemicals or intense heat;One factor affecting the choice of antimicrobial is the site to be treated. For example, harsh chemicals or intense heat cannot be used on human tissues. Another factor is the 2)Relative Susceptibility of the microbe - usually a method is chosen if it kills the strongest microbes and assumes the weaker ones will also be targeted. However, bacterial endopores, Mycobacterium species, protozoan cysts and infectious prions (proteins) are more resistant than any other to most methods; 3)Usage conditions (Environmental Conditions) - e.g. temperature or pH - chemicals react faster at higher temperatures which means that warm disinfectants generally work better than cooler ones.
Outline the 9 major categories of antimicrobial chemicals that are used as antiseptics and disinfectants. Give some examples and note how they impact the microbe.
<b>Phenol and Phenolics</b> Phenolics are compounds derived from phenol molecules that have been chemically modified by the addition of halogens or organic functional groups such as chlorine. They are intermediate- to low-level disinfectants that denature proteins and disrupt cell membranes in a wide variety of pathogens. <b>Alcohols</b> Alcohols such as isopropanol (rubbing alcohol) denature proteins and disrupt cell membranes; they are used either as 70-90% aqueous solutions or in a tincture, which is a combination of an alcohol and another antimicrobial agent. Alcohols are bactericidal, fungicidal, and virucidal against enveloped viruses; however, they are not effective against fungal spores or bacterial endospores. They are considered intermediate-level disinfectants. <b>Halogens</b> Halogens are the four very reactive, nonmetallic chemical elements: iodine, chlorine, bromine, and fluorine. Halogens are used as intermediate-level disinfectants and antiseptics to kill microbes in water or on medical instruments or skin. Although their exact mode of action is unknown, they are believed to denature enzymes. Iodine is used medically, whereas chlorine is more commonly used by municipalities to treat drinking water supplies, wastewater, and swimming pools. In hot tubs, bromine is more effective than chlorine, because it evaporates more slowly at high temperatures. Fluorine in the form of fluoride is an antibacterial added to drinking water and toothpaste to help reduce the incidence of dental caries. <b>Oxidizing Agents</b> Oxidizing agents such as hydrogen peroxide, ozone, and peracetic acid are high-level disinfectants and antiseptics that release oxygen radicals, which are toxic to many microbes, especially anaerobes. Hydrogen peroxide can disinfect and even sterilize surfaces, but it is not useful in the treatment of open wounds, because it is quickly neutralized by the catalase enzyme released from damaged human cells. Some Canadian and European municipalities use ozone rather than chlorine to treat their drinking water because ozone is more effective as an antimicrobial and does not produce carcinogenic by-products. Peracetic acid is an extremely effective sporicide used to sterilize equipment. <b>Surfactants</b> Surfactants are "surface active" chemicals. They include soaps, molecules that have both hydrophobic ends, which act primarily to break up oils during degerming, and negatively charged hydrophilic ends, which attract water. Detergents are positively charged organic surfactants such as quaternary ammonium compounds (quats), which disrupt cellular membranes. However, quats are considered low-level disinfectants because they are not effective against mycobacteria, endospores, or nonenveloped viruses, and some pathogens actually thrive in them. <b>Heavy Metals</b> Heavy metal ions such as arsenic, silver, mercury, copper, and zinc are low-level disinfectants that denature proteins. For most applications, they have been superceded by less-toxic alternatives, but silver still plays an antimicrobial role in some surgical dressings, burn creams, and catheters. <b>Aldehydes</b> Aldehydes are compounds containing terminal —CHO groups. Classified as high-level disinfectants, they cross-link organic functional groups in proteins and DNA. A 2% solution of glutaraldehyde and a 37% aqueous solution of formaldehyde (called formalin) are used to disinfect or sterilize medical or dental equipment and in embalming fluid. <b>Gaseous Agents</b> Many items, such as plastic laboratory ware, artificial heart valves, mattresses, and dried foods, cannot be sterilized easily with heat or water-soluble chemicals, nor is irradiation always practical. However, such items can be sterilized within a closed chamber containing highly reactive gases such as ethylene oxide, propylene oxide, and beta-propiolactone, which denature proteins and DNA by cross-linking organic functional groups, thereby killing everything they contact without harming inanimate objects. These gases are explosive and potentially carcinogenic. <b>Enzymes</b> Antimicrobial enzymes are enzymes that act against microorganisms. Scientists, food processors, and medical personnel are researching ways to use natural and artificial antimicrobial enzymes to control microbes in the environment, inhibit microbial decay of foods and beverages, and reduce the number and kinds of microbes on medical equipment. One exciting development is the use of an enzyme to eliminate the prion that causes variant Creutzfeldt-Jacob disease. <b>Antimicrobials</b> Antimicrobials include antibiotics, which are produced naturally by microorganisms, semisynthetics, which are chemically modified antibiotics, and synthetics, which are wholly synthetic antimicrobial drugs. These compounds are typically used to treat disease, but can also function as intermediate-level disinfectants.
How would a -static versus a -cidal graph change the microbial growth curve?
A -static graph would change the microbial growth curve after the log phase and give the graph a longer period of a stationary phase, because -static refers to the inhibition of microbes A -cidal graph would have an almost immediate death phase, because -cidal refers to destroying microbes.
How does an autoclave achieve sterilization?
An autoclave is a device consisting of a pressure chamber, pipes, valves, and gauges that uses steam heat under pressure to sterilize chemicals and objects that can tolerate moist heat.
What are the three ways chemical methods of control attack microbes?
Chemical agents adversely affect-- 1) microbes' cell walls 2) Cytoplasmic membranes 3)Proteins 4)DNA
What is decimal reduction time?
Decimal reduction time (D) is the time required to destroy 90% of the microbes in a sample.
What is degerming?
Degerming - is the removal of microbes from a surface by scrubbing, whether that surface is human skin or a table top e.g. washing hands;
What is dessication and what does it achieve?
Desiccation, or drying, has been used for thousands of years to preserve such foods as fruits, peas, and yeast. It inhibits microbial growth because metabolism requires liquid water.
What is disinfection and how is it achieved
Disinfection - the use of physical or chemical agents to inhibit or destroy microbes particularly pathogenic ones from inanimate objects. The process of disinfection does not guarantee elimination of all pathogens e.g wiping a surface with 10% bleach;
How are powders and oils sterilized?
For substances such as powders and oils that cannot be sterilized by moist heat, sterilization can be achieved using dry heat at much higher temperatures for longer times. Complete incineration is the ultimate means of sterilization.
Why is heat an effective method of control?
Heat is one of the older and more common means of microbial control. High temperatures denature proteins, interfere with the integrity of cytoplasmic membranes and cell walls, and disrupt the function and structure of nucleic acids. Microorganisms vary in their susceptibility to heat.
What is an in-use test and how does it evaluate agent effectiveness?
In-use test- in this procedure, swabs are taken from actual objects both before and after the application of a disinfectant or an antiseptic. The swabs are then inoculated into appropriate growth media, which after incubation are examined for microbial growth
What is lyophilization and what does it achieve?
Lyophilization, or freeze-drying, preserves microbes and other cells for many years. In this process, scientists freeze a culture in liquid nitrogen or frozen carbon dioxide, then remove the water via a vacuum. Lyophilization prevents the formation of large damaging ice crystals, leaving enough viable cells to enable the culture to be reconstituted many years later.
Why does pasteurized milk still spoil after a week in the fridge?
Microbes survive pasteurization but they do not cause spoilage because of proper refrigeration
What is microbial death?
Microbial death is defined as the loss of ability to reproduce in ideal conditions. This can be used to evaluate the action of an antimicrobial because the death rate is usually constant over time for any particular microbe in a certain set of conditions
What is pasteurization and how is it achieved?
Pasteurization - is the use of heat to kill pathogens and reduce the number of spoilage microorganisms in food and beverages. Milk, fruit juices, wine, and beer are commonly pasteurized to prevent them spoiling. This is done either by heating
What conditions ensure effective pasteurization?
Pasteurization, a method of heating foods to kill pathogens and control spoilage organisms without altering the quality of the food, can be achieved by several methods: the historical (batch) method at 63°C for 30 minutes, flash pasteurization at 72°C for 15 seconds, and ultrahigh-temperature pasteurization at 134°C for 1 second.
What is the Phenol coefficient?
Phenol Coefficient - Phenol was one of the first antiseptic used during surgery in the late 1800s so acts somewhat like a gold standard. Therefore you can compare the effectiveness of agents at control microbes with that of Phenol which gives you the phenol coefficient. If the ratio is greater than 1.0 then the agent is more effective than Phenol
What do refridgeration and freezing achieve?
Refrigeration (temperatures between 0°C and 7°C) halts the growth of most pathogens, which are predominantly mesophiles. Slow freezing at temperatures below 0°C is effective in inhibiting microbial metabolism; however, many vegetative bacterial cells, bacterial endospores, and viruses can survive subfreezing temperatures for years.
What is sanitization and how is it achieved?
Sanitization - is the process of disinfecting plates and utensils used by the public to reduce the number of pathogenic microbes so as to meet acceptable public health standards. Dishes are disinfected in a dishwasher at home, but are sanitized in a dishwasher in a restaurant.
What is sterilization and how is it achieved?
Sterilization - the removal or destruction of all microbes, including viruses and bacterial endospores (but not prions). This eradicates all potentially pathogenic microbes, but some non-pathogenic microbes may still persist e.g. autoclaving;
How is sterilization different from disinfection?
Sterilization is absolute in killing all microbes. Disinfection simply reduces the amount of microbes present in an area.
What is the Kelsey-Sykes capacity test and how does it evaluate effectiveness?
The Kelsey-Sykes capacity test - is an alternative to the use-dilution test that is the standard in the European Union to determine the capacity of a given chemical to inhibit bacterial growth. Researchers add a suspension of a bacterium to a suitable concentration of a chemical being tested. Then at predetermined times they move samples of the mixture into growth medium containing a disinfectant deactivator. After incubation for 48 hours, turbidity in the medium indicates that bacteria survived treatment. Lack of turbidity, indicating lack of bacterial reproduction, reveals the minimum time required for the disinfectant to be effective.
What is the thermal death point and thermal death time?
The thermal death point- is the lowest temperature that kills all cells in a broth in 10 minutes thermal death time- is the time it takes to completely sterilize a particular volume of liquid at a set temperature
Describe how different types of radiation (ionizing and non-ionizing) influence microbial molecules?
There are two types of radiation: Particulate radiation consists of high-speed subatomic particles freed from their atoms, whereas electromagnetic radiation is atomic energy without mass traveling at the speed of light. Ionizing radiation is electromagnetic radiation with wavelengths shorter than 1 nm, such as electron beams, gamma rays, and X rays. It creates ions that produce effects leading to the denaturation of important molecules and cell death. Nonionizing radiation, such as ultraviolet light, visible light, infrared light, and radio waves, has wavelengths longer than 1 nm. Of these types, only ultraviolet light has sufficient energy to be a practical antimicrobial agent. It causes pyrimidine dimers, which can kill affected cells.
What factors contribute to the development of resistance?
There is little evidence that the extensive use of antimicrobial chemicals in household cleansers and personal care products enhances human health; however, it does promote the development of strains of microbes resistant to antimicrobial chemicals. This is because, when susceptible cells die, they reduce competition for resources, allowing any remaining resistant cells to proliferate. Many experts therefore recommend limiting the use of such chemicals to food handling and health care involving high-risk patients and newborns.
What is the use-dilution test and how does it evaluate effectiveness?
Use-dilution test - a researcher dips several metal cylinders into broth cultures of bacteria, briefly dries them, then immerses each into a different dilution of the disinfectants being evaluated. After 10 minutes, the cylinders are removed and incubated. The most effective agent is the one that entirely prevents microbial growth at the highest dilution
How does the microbial death rate look like when plotted on a log scale?
When plotted on a semi-log graph, it produces a straight line because the death rate is constant
Why can filtration be used as a method of microbial control?
When used as a method of microbial control, filtration is the passage of air or a liquid through a material that traps and removes microbes. Some membrane filters manufactured of nitrocellulose or plastic have pores small enough to trap the smallest viruses and even some large protein molecules. HEPA (high-efficiency particulate air) filters remove microbes and particles from air.
How is handwashing classified using the terminology of microbial control above?
it is classified as degerming
How is sanitization different from pasteurization?
sanitization is involved in cleaning objects Pasteurization is heating of beverages and food
What would the perfect antimicrobial method/agent be?
•inexpensive; •fast-acting; •stable during storage •harmless to humans; •effective against all types of microbes. A pefect animicrobial agent would control the growth and reproduction of every type of microbe while being harmless to humans, animals, and objects.