Microbiology chp 9 notes PDF

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Micro chp 9 notes 9.1 Disinfection Sterilization antisepsis/degermation decontamination/sanitization Bactericide- an agent that kills bacteria germicide An agent lethal to non-endospore-forming pathogens. microbicides Chemicals that kill microorganisms. sepsis The state of putrefaction; the presence of pathogenic organisms or their toxins in tissue or blood. Asepsis- a condition free of viable pathogenic microorganisms Antiseptic- a growth-inhibiting agent used on tissues to prevent infection Bacteristatic- any process or agent that inhibits bacterial growth microbistatic The quality of inhibiting the growth of microbes 9.2 thermal death time (TDT) The least time required to kill all cells of a culture at a specified temperature. thermal death point (TDP) The lowest temperature that achieves sterilization in a given quantity of broth culture upon a 10-minute exposure. Examples: 55°C for Escherichia col, 60°C for Mycobacterium tuberculosis, and 120°C for endospores.

pasteurization Heat treatment of perishable fluids such as milk, fruit juices, or wine to destroy heat-sensitive vegetative cells, followed by rapid chilling to inhibit growth of survivors and germination of spores. It prevents infection and spoilage. Autoclave- a sterilization chamber that allows the use of steam under pressure to sterilize materials. The most common temperature/pressure combination for an autoclave is 121 degrees celsius and 16 psi desiccation To dry thoroughly. To preserve by drying. lyophilization A method for preserving microorganisms (and other substances) by freezing and then drying them directly from the frozen state. radiation Electromagnetic waves or rays, such as those of light given off from an energy source. irradiation The application of radiant energy for diagnosis, therapy, disinfection, or sterilization. 9.3 Aqueous- referring to solutions in which water is used as the solvent tincture A medicinal substance dissolved in an alcoholic solvent.

Chapter Summary 9.1 Controlling Microorganisms • Microbial control methods involve the use of physical and chemical agents to eliminate or reduce the numbers of micro- organisms from a specific environment to prevent the spread of infectious agents, retard spoilage, and keep commercial products safe. • The population of microbes that cause spoilage or infection varies widely, so microbial control methods must be adjusted to fit individual situations. • The type of microbial contiol is indicated by the terminciogy used. Sterilization agents destroy all viable organtsms, including viruses. Antisepsis, disinfection, decontamination/ sanitization, and antisepsis/degermation reduce the nuinbers of viable microbes to a specified level.

• Antimicrobial agents are described actording to their ability to destroy or inhibit microbial growth. Microbicidal agents cause microbial death. They are described by what they arecidal for: sporicides, bactericides, fungicides, and viricides. • An antiseptic agent is applied to living tissue to destroy or inhibit microbial growth. • A disinfectant agent is used on inanimate objects to destroy vegetative pathogens but not bacterial endospores. • Decontamination/sanitization reduces microbial numbers on inanimate objects to safe levels by physical or chemical means. Micrebiel • Microbial death is defined as the permanent loss of reproductive capability in microorganisms. • Antimicrobial agents attack specific cell sites to cause microbial death or damage. The four major cell targets are the cell wall, the cytoplasmic membrane, biosynthesis pathways for DNA or RNA, or protein (enzyme) function.

9.2 Methods of Physical Control • Physical methods of microbial control include heat, cold, radiation, drying, filtration, and osmotic pressure. • Heat is the most widely used method of microbial control, It is used in combination with water (moist heat) or as dry heat (oven, flames). • The thermal death time (TDT) is the shortest length of time required to kill all microbes at a specific temperature. • The thermal death point (TDP) is the lowest temperature at which all microbes are killed in a specified length of time (10 minutes). • Autoclaving, or steam sterilization, is the process by which steam is heated under pressure to sterilize a wide range of materials in a comparatively short time (minutes to hours). • Boiling water and pasteurization of beverages disinfect but do not sterilize materials. • Dry heat is microbicidal under specified times and temperatures. Flame heat, or incineration, is microbicidal. • Chilling, freezing, and desiccation are microbistatic but not microbicidal. They are not considered true methods of disinfection because they are not consistent in their effectiveness. • lonizing radiation (cold sterilization) by gamma rays and X rays is used to sterilize medical products, meats, and spices. It damages DNA and cell organelles by producing disruptive ions.

• Ultraviolet light, ionizing radiation, has limited penetrating ability. But it is proving to be very useful for terminal disinfection of hospital rooms. • Decontamination by filtration removes microbes irom heat- sensitive liquids and circulating air. The pore size of the filur determines what kinds of microbes are removed. • The addition of high amounts of salt or sugar to food results ine preservation through osmotic pressure.

9.3 Chemical Agents in Microbial Control • Chemical agents of microbial control are classified by their physical state and chemical nature. • Chemical agents can be either microbicidal or microbi- static. They are also classified as high-, medium-, or low-level germicides. • Factors that determine the effectiveness of a chemical agent include the type and numbers of microbes involved, the mate- rial involved, the strength of the agent, and the exposure time. • Halogens are effective chemical agents at both microbicidal and microbistatic levels. Chlorine, iodine, and iodophors are examples. • Phenols are strong microbicidal agents used in general disinfection. • Alcohols dissolve membrane lipids and destroy cell proteins. Their action depends upon their concentration, but they are generally only microbistatic. • Oxidizing agents are versatile microbicides that can be used as antiseptics for wounds and disinfectants for utensils. A high concentration is an effective sporicide. • Detergents reduce cytoplasmic membrane surface tension, causing membrane rupture. Cationic detergents, or quats, are low-level germicides limited by the amount of organic matter present and the microbial load. • Aldehydes are potent sterilizing agents and high-level disin- fectants that irreversibly disrupt microbial enzymes. • Ethylene oxide and chlorine dioxide are gaseous sterilants that work by alkylating protein and DNA....