Control of Microbial Growth Review of Vocabulary Sterilization

Control of Microbial Growth

Review of Vocabulary �Sterilization: is the destruction of all forms of microbial life w/particular attention to bacterial spores �Disinfection: refers to the destruction of pathogenic organisms on an inanimate object. �Antisepsis (Asepsis): refers to the destruction of pathogens on a living object, ex. Skin surface.

Review of Vocab �Germicide: any chemical agent that kills microorganisms. �Bactericide: an agent that destroys bacteria. �Fungicide: an agent that destroys fungi. �Viricide: an agent that destroys viruses. �Bacteriostatic Agent: prevents the further multiplication of bacteria w/o necessarily killing all that are present.

Conditions Affecting the Use of Germicides �Temperature: germicides are more effective @ high temps. �Type of microorganisms: microorganisms vary in susceptibility depending on things like composition of cell wall, the presence of a capsules & the ability to form spores or cysts. �Environment: can affect the activity of a germicide ex. It can form a shield that reacts w/the germicide.

Physical Methods of Control �Physical methods for controlling the growth of microorganisms can be divided into heat & nonheat methods. �The lowest tempt. where all microorganisms are killed in 10 minutes is thermal death point. �Thermal Death Time: min. amount of time needed to kill pathogens @ a given tempt. �Decimal Reduction Time: time where 90% of all microorganisms are killed.

Dry Heat �Dry heat kills microorgansisms by reacting w/& oxidizing their proteins. Examples of dry heat: �Incineration devices like Bunsen burner �Hot Air oven (tempt. Over 170 C for 2 hours = sterilization)

Moist Heat �Moist heat is used to kill microorganisms in such things as boiling water. �Most microbial growth is killed w/in 2 -3 minutes, but 2 -3 hours may be required for destruction of bacterial spores. �In moist heat, the microbial proteins undergo denaturation, a process where the 3 -d form of the microorganism reverts to a 2 -d form & the proteins break down.

Examples of Moist Heat �Autoclave- a high pressure device that superheats steam & requires only 15 minutes to achieve sterilization. �Pasteurization- is used to lower the bacterial content of milk & dairy products, it doesn’t reach sterilization. �Tyndallization (intermittent sterilization)liquids & other items are heated w/steam for 3 days to kill microorganisms & spores.

Non-heat Methods to control microbial growth �Filtration- a process where a liquid or gas passes through a series of pores small enough to retain (filter) microorganisms. Often used when heat sensitive materials like vaccines are to be sterilized. �Drying- removes water from cells which causes them to shrivel & die. �Cold temperatures- @ low tempts. Microbial growth slows, however it does not kill. However, @ freezing tempts, kills some microorganisms but not all.

Non-heat Methods to control microbial growth �Radiation- changes the chemical composition of microorganisms. Ex. Food & other materials subjected to gamma rays or x-rays. �Ultraviolet Light- non-ionizing radiation affects the nucleic acids & DNA of microorganisms which causes cell death. �Microwave – form of radiation that cause H 2 O molecules to vibrate rapidly causing heat that kills some microorganisms.

Chemical Methods of Control � Chemical agents are not intended to cause sterilization. Most just reduce the microbial populations to safe levels. � Criteria for selecting chemical agents (disinfectants or antiseptics) are the concentration of disinfectant to be used, whether the agent is a bactericidal or bacteriostatic, the nature of the material to be treated, whether organic matter will be present, the tempt & p. H @ which the chemical agent will be used, & the time available in which the chemical agent will be left in contact w/the surface treated.

Phenols & Phenolics �Phenols are one of the 1 st chemicals used as a disinfectant by Joseph Lister in the 1860’s. �Phenolics useful as antiseptics & disinfectants. �Both cause denaturing of microorganisms’ proteins & enzymes. �Ex. Lysol, & Hibiclens.

Halogens Among these antiseptics & disinfects are chlorine & iodine. �Iodine: is used as an alcohol & iodine mixture & includes Betadine, & Povidone. It’s used to denature the proteins of microorganisms & inhibit their function. �Chlorine bleach is used to disinfect objects & sanitize glassware.

Alcohols �Useful against bacteria & fungi, but it has no effect on spores. � 70% Ethyl Alcohol (Ethanol) is the most widely used alcohol. �Isopropyl Alcohol (Rubbing Alcohol) is used as an antiseptic & disinfectant. �Because alcohol evaporates quickly, it leaves no residue on skin prior to injections.

Heavy Metals have antimicrobial abilities. �Silver: used in the eyes of newborns to guard against infection & to cauterize wounds. �Copper is used to slow the growth of algae in swimming pools, fish tanks, & reservoirs. �Zinc is used in mouthwashes & as an antifungal agent in paints.

Soaps & Detergents �Soaps & detergents decrease the surface tension b/w microorganisms & surfaces thereby cleansing the surface. �Soaps emulsify the oily film on the body surface carrying oils, debris & microorganisms away. �Dtergents break down the cell membranes of microorganisms

Antibiotics inhibit the growth of microorganisms. �Examples �Penicillin- prevents gram positive bacterial from forming. It’s not just 1 antibiotic but an entire family of antibiotics. It includes penicillin F, G, X, ampicillin, amoxicillin, nafcillin, & ticarcillin. �First penicillins came from green mold but now most are man made.

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