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use-dilution test

used to evaluate effectiveness of disinfectants, antiseptic; 3 bacteria used: Salmonella choleraesuis, Staphylococcus aureus, Pseudomonas aeruginosa; metal carrier rings dipped in standardized cultures of test bacteria are placed in solution of disinfectant for 10 minutes at 20˚C. Rings are then carried to a medium that will permit the growth of any surviving bacteria

disk-diffusion method

used to evaluate the efficacy of a chemical agent; disk of filter paper is soaked with chemical and placed on inoculated agar plate and incubated with the test organism; if chemical is effective, a clear one representing the inhibition of growth can be seen around the disk


disrupts plasm membrane, denatures enzymes; rarely used except as standard of comparison due to irritating qualities and disagreeable odor


disrupts plasma membrane, denatures enzymes; derivatives of phenol that are reactive in presence of organic material; ex. O-phenylphenol


probably disrupts plasma membrane; disinfectant for skin; ex. triclosan; most effective against gram+ but has broad spectrum

biguanides (chlorhexidine)

disrupts plasma membrane; used for skin disinfection; bactericidal to gram+, gram-; nontoxic, persistent


iodine inhibits protein function, is strong oxidizing agent; chlorine forms the strong oxidizing agent hypochlorous acid which alters cell. components; iodine or chlorine may act alone or as components of inorganic, organic compounds


protein denaturation, lipid dissolution; bactericidal, fungicidal but not effective against endospores or nonenveloped viruses

heavy metals & their compounds

denatures enzymes & other essential proteins; heavy metals such as Ag or Hg are biocidal

soaps, detergents

surface-active agents; mechanical removal of microbes through scrubbing; many antibacterial soaps contain antimicrobials

acid-anionic sanitizers

surface-active agents; may involve enzyme inactivation or disruption; wide spectrum of activity; nontoxic, noncorrosive, fast-acting

quaternary ammonium compounds (cationic detergents)

surface-active agents; inhibits enzymes, denatures protein, disrupts plasma membranes; bacetricidal, bacteriostatic, fungicidal, virucidal against enveloped viruses; ex. Zephiran, Cepacol

organic acids

chemical food preservatives; inhibits metabolism (mostly affecting molds), mechanism of action not related to acidity; widely used to control mold and some bacteria in foods, cosmetics


chemical food preservatives; active ingredient is nitrite (produced by bacterial action on nitrate)-inhibits certain Fe-containing enzymes of anaerobes; prevents growth o Clostridium botulinum in food; imparts red color


denatures protein
very effective antimicrobials

gaseous chemosterilizers

denatures protein; ethylene oxide is most commonly used; excellent sterilizing agent esp. for objects that would be damaged by heat

peroxygens (oxidizing agents)

oxidation; for contaminated surfaces, some deep wounds; ozone is widely used as supplement for chlorination; peracetic acid; hydrogen peroxide

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