MCB 100 1st Edition Lecture 24 Outline of Last Lecture I. What is the difference between bacteriocidal and bacteriostatic? II. Factors that affect efficiency of a bacteriocidal treatment a. Speciesb. Material c. Biological factorsd. Environmental factors Outline of Current Lecture I. Killing microbes with heatII. RefrigerationIII. FiltrationIV. RadiationV. Antiseptics, disinfectants, and sanitizing agents VI. Controlling growth of microorganisms using osmotic pressureVII. Antibiotics and antimicrobial drugs VIII. General mode of action of antibioticsIX. General classes of antibiotics based on specific modes of action Current LectureI. Killing microbes with heat a. Antimicrobial treatments kill by damaging a vital cellular structure or by inhibiting a metabolic reactionb. Heat kills bacteria by denaturing proteins and nucleic acidsc. Heat disrupts the cell membrane structured. Most heat kills bacteria faster than dry heat because water has a higher heat capacity than air e. Steam, boiling water, and dry heat:i. Compressed steam is hotter than boiling water (use it to heat sample to a higher temperature)ii. Moist heat kills cells by denaturing proteins, nucleic acids, and the cell membrane causing cytoplasm to turn into a coagulated mass iii. Dry heat removes water from the cell and causes oxidation of organic matter, basically the bacteria slowly burn until they turn into little pieces of charcoal 1. Dry heat- used to sterilize metal or glass instruments that can take the heatThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.2. Tools should be dry to prevent rust and easier to hold3. Paper can catch on fire in a sterilizing oven 4. Paper or cloth are usually sterilized in an autoclave using moist heat and then placed in a drying oven (130-150 degrees C) f. Pasteurizationi. Disinfection of beverages using a minimal amount of heat ii. Beverages such as milk, fruit juices, beer, and wine are easily contaminated with microorganisms during collection and processingiii. Contaminating microorganisms can cause spoilage of the product or may be human pathogens iv. Pasteurization is the application of heat to a liquid to kill potential agents of infection and spoilage without destroying the product's taste or nutritional value v. Milk is typically heated to 72 degrees C for 15 seconds in a special heat exchanger (flash method), OR 65 degrees C for 30 minutes (batch method)---> this amount of heat is sufficient to kill most viruses and vegetative stages of bacteria and fungi vi. Pasteurization of milk is designed to kill non-spore forming pathogens, especially:1. Mycobacterium bovis and Mycobacterium tuberculosis (TB)2. Coxiella burnetii (Q-fever)3. Salmonella typhi (typhoid fever)4. Campylobacter jejuni (gastroenteritis)5. Listeria monocytogenes (listeriosis) II. Refrigeration (bacteriostatic treatment)a. Refrigeration slows or stops bacterial growth but it does not kill them b. Cold temperatures are generally bacteriostatic rather than bacteriocidal c. Some microorganisms will grow in the refrigerator, but they grow slowly d. Refrigeration prevents growth of most disease causing bacteria because they are adapted for growth in the human bodye. Freezing kills some bacteria by causing the formation of ice crystals that can disrupt the cell membrane, but most bacteria can survive freezing if they are put into a 15% solution of glycerol II. Filtration used to sterilize a liquid (Sterilizes without heat)a. Bacteria are generally larger than 0.5 mm in diameter, so if you run a fluid through a filter with a pore size of 0.2 mm the bacteria will be trappedb. Filtration is used when the sample is sensitive to heatc. Examples of solutions that are filter sterilized include: vitamin solutions, some aminoacids, and cold-filtered beer II. Killing microorganisms with radiationa. Two types of radiation used in antimicrobial applications are: i. UV light and ionization radiation ii. UV light- used to kill bacteria in aquariums and on the surface of instruments or lab bench tops. Germicidal lamps emit UV light; UV light causes damage toDNA that increases the frequency of potentially fatal mutations (distorts doublehelix) iii. Ionization radiation (gamma rays, x-rays) damages DNA- breaks a wide variety of covalent bonds- causes massive deletion of genes/chromosomes; used to treat fruits and vegetables to slow the growth of damaging bacteria) 1. Irradiation is used to kill microorganisms on some foods (strawberries, beef, poultry)2. Ionization radiation may have less effect on the taste and texture of the food product than traditional treatments that involve heat 3. Food doesn’t become radioactive when it is treated with radiation II. Antiseptics, Disinfectants, and Sanitizing Agentsa. Antiseptics and disinfectants are chemical agents used to kill bacteria b. an antiseptic is used on human skin and mucous membranesc. A disinfectant is used on inanimate objects like table tops i. Properties of an ideal disinfectant:1. Selective toxicity, lethal to bacteria but not harmful to humans 2. Good solubility in water3. Stable at room temperature4. Toxicity at room temperature, able to kill bacteria without adding heat5. Capacity to penetrate6. Non-corrosive7. Non-staining8. Not offensive (no bad smell) ii. Solvents- denature proteins and disrupt the cytoplasmic membrane structure (ex. Phenols, cresols, and alcohols)iii. Oxidizing agents- oxidation of organic compounds- breaking them into fragments (ex. Halogens, bleach, hydrogen peroxide, and sterilizing gas ethylene oxide) iv. Heavy metals- inhibition of enzymes--> (proteins are often stabilized by non-covalent bonds) (ex. Mercury, lead, silver) v. Soaps and detergents- can denature proteins and disrupt the cytoplasmicmembrane structure, but they are weak and mostly just act to help clean a surface (ex. Quaternary ammonium compounds- quats such as benzalkonium chloride)1. Soap: a salt of a fatty acid whereas a detergent is a synthetic derivative of a fatty acid2. Detergents are more soluble in water than soap and less likley to leave a soap scum 3. Soaps and detergents have a mild killing power against bacteria- they are surfactants that reduce the surface tension of water and increasesolubility of oily particles--> this makes it easier to wash bacteria off of the skin and may kill a few of them by disrupting cell membranes (Some bacteria are resistant to