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Articles: Science
Chemical Control
- Mr. ThummalaSanathReddy Reddy
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Chemical Control Of Microorganisms Sterilization - killing all organisms in or on something Disinfection - reduction of pathogens till harmless Antiseptic - used externally on tissue to destroy or inhibit organisms Disinfectant - used on surfaces (don't kill spores) Sanitizer - used on food prep equipment / utensils to reduce number Bacteriocidal - kill bacteria Bacteriostatic - prevent growth Factors that affect death rate: o Number of bacteria present (more means longer) o Environmental factors (temp, pH) o Dosage of agent used o Presence of other inhibitory stuff (organic material) o Bacterial factors (resistance) Relative resistance of Microorganisms Highest resistance Spore forming organisms Moderate resistance Protozoan cysts Hepatitis B Poliovirus Mycobacterium tuberculosis Staph. aureus Pseudomonas Least resistance Most bacteria Yeasts Phenol Coefficient Use Salmonella typhi and Staph aureus as test organisms Compare agent's effectiveness against phenol (1) Higher numbers, more effective than phenol Choosing agents: Fast acting Work on bacteria w/o being poisonous to people (even solvent) Penetrate material without staining Be stable when stored Inexpensive Smell good Mechanisms of action Attack cell wall/membrane - (soaps, alcohol) Attack proteins - denature Temporary - Bacteriostatic Permanent - Bacteriocidal Specific Agents Soaps & Detergents Solubilize membranes, mildly alkaline Bars of soap in public restrooms is bad idea 100+ strains isolated once Quaternary ammonium compounds Many detergents Clean and disinfect Halogens Chlorine- active ingredient in bleach Iodine - topical antisepsis Bromine - used in hot tubs (doesn't smell like chlorine does) Heavy metals Silver nitrate - gonococcus Merthiolate (mercury) Silver and gold Copper sulfate in pipes - prevents algae growth Selenium - dandruff shampoo to kill fungi Alcohols Solubilize membranes and denature proteins 70% works better than 95% Phenols Solubilize membranes and denature proteins Lysol - action remains on surfaces for days Creosote has phenol derivative Oxidizing agents H2O2 is used to kill anaerobes in wounds Aldehydes Formaldehyde, Glutaraldehyde Quickly inactivates enzymes Good on most resistant organisms Toxic to tissues, not good antiseptic Gaseous compounds Ethylene oxide - only accepted chemical sterilant Used in special autoclave like machine Very toxic Used on spices, drugs, surgical supplies, plasticware

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