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Transcript
CONTROL OF MICROORGANISMS BY PHYSICAL AND CHEMICAL AGENTS I. II. Types of Control A. STERILIZATION: Process by which all living organisms are destroyed or removed from an object or habitat B. Disinfection: Killing, inhibition or removal of microorganisms that may cause disease Disinfectants: Agents (chemical) used to carry out disinfection: Not safe for use on skin or membrane surfaces: Does not sterilize: Viable spores may remain Used on: Dishes Linens Walls Floors Rest rooms Laboratory benches C. Sanitization: Closely related to disinfection: Microbial population reduced to levels considered safe by public health standards: Sanitizers: Used to clean dishes and utensils in restaurants D. Generalities Microorganisms occur almost everywhere in the environment Media is contaminated when it is made Must be sterilized before use Equipment must be sterilized before use Sterile: Complete absence of living organisms Sterilization techniques A. Autoclave: Used to sterilize media Heat under pressure (15 lbs psi) to 121oC (247oF) Heat to above the boiling point of water to kill any endospores that may be present Endospores are much more resistant to heat than vegetative cells Autoclave is a giant pressure cooker: Used to prepare canned foods at home and commercially Food is heated and held under pressure to temperature high enough to kill endospores B. Membrane Filtration Used to sterilize media that can't be autoclaved Heat may destroy essential ingredients or cause salts to precipitate out Filter has holes too small for bacteria to get through Allows the passage of liquids Microorganisms trapped on the filter C. Hot Air Oven: Used to sterilize: Glassware Hypodermic needles Pipettes Test tubes Petri dishes etc. Glassware heated at 170oC for at least 90 minutes Temp. and time enough to kill endospores D. Gas Sterilization: Used for solid materials that can't be heated: Plastics such as: Petri dishes Flasks Pipettes Beakers Surgical gloves Placed in gas chamber and exposed to toxic gas (ethylene oxide) long enough to kill all microorganisms present Gas is removed Allowed to air for 8 to 10 days Gets rid of gas which is toxic to humans E. Radiation: X rays and ultra violet are also used to sterilize plastics F. III. Incineration: Used to dispose of: Contaminated disposable items Lab animals Flame microbiological loops ANTIMICROBIAL AGENTS A. Chemicals used to kill or inhibit the growth of microorganisms Synthetic or natural products Cidal agents - kill B. Mode of action: 1. Bind tightly to cell structures -can't be removed by washing 2. Cause cell to lyse (bacteriolytic agents) C. Germicide Cidal agent with broad application a. disinfectants - kill bacteria - not safe for use on skin or membrane surfaces Used on: Dishes Linens Walls Floors Rest rooms Laboratory benches b. Antiseptics - kill bacteria - safe for use on skin and membrane surfaces D. Static agents Do not kill - but inhibit bacterial growth Many bind loosely to ribosomes -inhibit protein synthesis Must be continuously present - if removed organism grows again Used as food preservatives: NaNO3 and NaNO2 used as preservatives in cured meats Prevents growth of Clostridium botulinum NaNO2 converted to nitrous acid and nitroso cpds. in stomach (carcinogens) E. Antibiotics Chemical product of biological origin - kills or inhibits microorganisms Derived from microorganisms Penicillium penicillin, griseofulvin Streptomyces Streptomycin, tetracycline, erythromycin, chloramphenicol, Bacillus peptide antibiotics (bacitracin, polymyxin) Penicillin - first antibiotic discovered Discovered by Sir Alexander Fleming Acts against actively growing cells Prevents the synthesis of peptidoglycan Most effective against Gram positive cells Eukaryotic cells not affected - don't produce peptidoglycan Effective against: Streptococcus pyogenes Streptococcus pneumoniae Staphylococcus aureus Neisseria gonorrhea Treponema palladium F. Strep throat and Scarlet fever Lobar pneumonia Toxic shock syndrome Gonorrhea Syphilis Bacterial resistance Develops as the result of mutation or the acquisition of a resistance plasmid Multiple resistances - resistant to more than one antibiotic Two Types of resistance 1. Inherent 2. Acquired