Control of Microbial Growth

1. Control of Microbial Growth

2. 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.

3. 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.

4. 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.

5. Physical Methods of Control • Physical methods for controlling the growth of microorganisms can be divided into heat & non-heat methods. • The lowest tempt. where all microorganisms are killed in 10 minutes is the 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.

6. 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)

7. 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.

8. 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.

9. 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.

10. 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 H2O molecules to vibrate rapidly causing heat that kills some microorganisms.

11. 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 & pH @ which the chemical agent will be used, & the time available in which the chemical agent will be left in contact w/the surface treated.

12. Phenols & Phenolics • Phenols are one of the 1st 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.

13. 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.

14. 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.

15. Heavy Metalshave 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.

16. 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

17. 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.

18. The End