Chemical Control Agents

Lecture 09 [Notes]

Major Antimicrobial Chemical Agents
A. Phenol and Phenolic Compounds Carbolic acid was first used by Lister in the 1860's and became the standard against which all other disinfectants were compared; phenol is ineffective against spores, works in combination with soap, a poor viricide; good in saline solution or at warm temperature, good fungicide; both Semmelweiss and Pasteur had provided a basis for using this compound as a standard; after World War II (1948­1958) a variety of phenol derivatives came into being ­ called phenolics; ortho­phenyl­phenol is a CRESOL and is found in Lysol and other Cresols are used in Creosote as environmental disinfectants and fungicides HEXYLRESORCINOL reduces surface tension and is used as an antiseptic, it is found in some mouthwashes and in Sucrets; HEXACHLOROPHENE (G­11) was widely used as a topical scrub and skin antisepsis; in 1972 it was found that this compound is easily absorbed through the skin and could cause neurological damage, such as brain damage to new borns, major compound in PhiSoHex; still found in Ipana toothpaste, Mum Deodorant, and Dial soap; remains an effective skin mildicide These compounds work by denaturing cell proteins, inactivating enzymes, and damaging cell membranes During the 1948­58 period the Phenol­Coefficient Test was replaced by a Use­Dilution Test, the AOAC test, which tested chemical products under the conditions in which they would actually be used; the Phenol­Coefficient Test is an IN VITRO analysis of the state of the organism B. Halogens (Iodine, Chlorine, Bromine, Fluorine) Iodine is one of the oldest (300­400 years) and most effective germicidal agents; broad spectrum bactericide, good fungicide, some viricidal action, will kill spores, excellent disinfectant; also effective against protozoa (amebas) only slightly soluble in water; available as a tincture dissolved in alcohol (KI, NaI), problems arise as alcohol evaporates and concentration of iodine increases ­ may cause burning of skin IODOPHORS are combinations of iodine and organic molecules (hydrocarbons) which are more effective, non­irritating, good surfactants and non­staining; examples are Wescodyne and Betadine; they work by inhibiting enzyme action Chlorine is used as a gas dissolved in water or in combination with other chemicals; mode of operation is not completely understood but appears to be a strong oxidizing agent as result of the following reaction: Cl2 + H2O ­­­> HCl + HClO ­­­> HCl + [O] HYPOCHLORITES are used domestically and industrially for disinfection; first advocated by Semmelweiss (1846­1848) to reduce incidence of childbed fever in hospitals; have a broad spectrum of kill; NaOCl (sodium hypochlorite) is active agent in Clorox CHLORAMINES are a combination of chlorine and ammonia; they are slow to volatilize and release the chlorine over long periods of time; they are effective in contact with organic matter and are used in root canal surgery and for general wound disinfection; Halazone is an example of one used for emergency disinfection of water C. Alcohols Effective killers of vegetative bacteria and fungi but NOT effective against endospores and most viruses. They work by denaturing proteins and dissolving lipids. Effectiveness of various alcohols increases with increasing molecular weight, unfortunately their negative impact on skin also increases; used to enhance the effectiveness of other chemical agents D. Heavy Metal and their Compounds These are the most ancient of antiseptics and disinfectants. They were used by Egyptians, in the form of gold ointments and dust and often buried with the corpse or mummies to provide salves and ointments in the after life. They have an Oligo­ dynamic Action (all encompassing) and are extremely effective. They work because of the strong affinity of the metals to proteins; copper ionizes in water and controls algae, DaVinci and others rubbed gold dust in ointments for wounds. This created enzymatic bindings; metallic ions bind up to and adhere to the sulf­hydryl groups in proteins, stronger concentrations act as protein precipitants. The action of heavy metals at low concentrations has a subtle interference on the cell's metabolism SILVER was used as an antiseptic as a 1% silver nitrate solution (Argyrol) and was used in the eyes of newborn ­ this practice has been largely replaced by the use of antibiotics. MERCURIALS, inorganic mercury compounds, had a long history with their heyday during WW I, not as toxic as Iodine, and no burning of the skin upon application. Replaced by organic mercury compounds such as Mercurochrome, Methiolate and Metaphen, they are used as skin antiseptics but their effects are reversed when washed off ZINC is used in combination with chlorine compounds as a mouthwash and in other combinations is an effective fungicide ORGANOMETALLICS (organically activated metals ­ heavy metals, organic radicals such as alcohol); concept is 30­40 years old good against Gram + cocci, diphtheroids, spore­forming rods, TB and like organisms; may be effective against viruses, extremely effective against mycoses; virtually no effective­ ness against Gram ­ rods; Tributyl tin is example, also has deodorizing quality E. Soaps and Synthetic Detergents Act by mechanical removal, surface tension depressants; usually mildly germicidal, wetting agents. A detergent is any surface tension depressant (keeps organisms spread out) 1. Anionic detergents ­ negatively charged portion of molecule is active part; sodium laurel sulfate, DREFT, not too germicidal; work against Gram +; C12H25OSO3 attached to Na+ 2. Cationic detergent ­ positive portion of molecule is active part; very germicidal, CPC (cetyl pyridinium chloride) used in mouthwash and toothpaste; Cepacol (mouthwash); cause inactivation of enzymes and destruction of cell membrane Quatenary ammonium compounds ­ can act in concentrations as low as 1:30,000 and still be cidal; Zephiran, Phemerol, Diaparene, Ceepryn are all examples. 3. Non­ionic detergents ­ not germicidal, good surfactants, primarily used as laundry detergents F. Acids and Alkalizers They cause changes in the microbe's microenvironment; alkalizers work against Gram + cocci, rods, spore­formers, some viruses; Mycobacterium species are resistant to alkali; acidity ­ if microenvironment is maintained at about pH 3, organisms begin to die off, the longer it is kept there the greater the die off; used in food preservation techniques G. Oxidizers supply boundless oxygen; in combination with mercurials these have been used in wound cleaning; H2O2 (hydrogen peroxide); KMnO4 (potassium permanganate); Zinc peroxide H. Dyes used primarily in selective and differential media; can be used intravenously and as pills or applied to skin in liquid form; some are strong mutagenic agents; action unclear Gaseous Chemosterilizers (Disinfectant Aerosols) particles should be between 1­5 microns to be most effective 1. Formaldehyde ­ (Formalin is 40%) ­ toxic to humans; work best in dry environment ­ better penetration; crystalizes at room temperature 2. Ethylene Oxide ­ volatile, flammable, good penetration 3. Beta­propriolactone ­ non­inflammable, more antimicrobial, less penetrating 4. Glutaraldehyde - effective at room temperature; microbial activity increased with heat; effective against certain viruses, endospores, and Mycobacterium species; may irritate skin or eyes; examples: Sonacide, Cidex, Metracide
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