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
Back to Homepage
Back to BIOL 2275 Start Page

Email: demmeluth@hotmail.com