Chemical Agents in Microbial Control

• Antimicrobial chemicals:

  • Solid

  • Liquid

  • Gaseous

  • For convenience, solid or gaseous antimicrobial chemicals are dissolved in water, alcohol, or a mixture of the two
• Aqueous solutions: • Solutions containing pure water as the solvent
• Tinctures: • Antimicrobial chemicals dissolved in pure alcohol or water–alcohol mixtures
• Desirable Qualities of a Germicide

  • Rapid action in low concentrations

  • Solubility in water or alcohol and long-term stability

  • Broad-spectrum microbicidal action without toxicity to human and animal tissues

  • Penetration of inanimate surfaces to sustain a cumulative or persistent action

  • Resistance to becoming inactivated by organic matter

  • Noncorrosive or nonstaining properties

  • Sanitizing and deodorizing properties

  • Affordability and ready availability
• • No chemical can completely fulfill all requirements

  • Glutaraldehyde & hydrogen peroxide somewhat ideal

  • Polyhexamethylene-guanidine hydrochloride (PHGH) also seems to satisfy the requirements and is able to destroy spores.
• Germicides

  • Evaluated based on its effectiveness in destroying microbes
  • High, intermediate, low
• High-Level Germicides

  • Kill endospores
  • Sterilants if properly used
• High-Level Germicides are used on critical items that are not heat-sterilizable:

  • Catheters

  • Heart-lung equipment

  • Implants
• Intermediate-Level Germicides

  • Kill fungal
  • but not bacterial spores, resistant pathogens such as the tubercle bacillus, and viruses
• Low-Level Germicides:

  • Eliminate only:
  • Vegetative bacteria
  • Vegetative fungal cells
  • Some viruses

  Used in cleaning Noncritical Materials
• Factors Affecting the Microbicidal Activity of Chemicals

  • Nature of microorganisms being treated

  • Nature of material being treated

  • Degree of contamination

  • Time of exposure

  • Strength and chemical action of the germicide
• Cellular Targets of Germicides Modes of action of germicides are to attack cellular targets:

  • Proteins

  • Nucleic acids

  • Cell wall

  • Cell membrane
• Dilutions – small volume of liquid chemical (solute) is diluted in a larger volume of solvent to achieve a certain ratio. E.g. Lysol is usually diluted 1:200, Chlorine in very diluted concentrations are expressed in parts per million (ppm)
• Percentage solutions-solute is added to water to achieve certain percentage in solution. E.g. 50% Alcohol, 95% Alcohol
• • Most compounds require adequate contact time to allow the chemical to penetrate and to act on the microbe present
• Halogens - are group of nonmetallic elements
• Halogens


  Fluorine, bromine, chlorine, iodine
• Halogens


  Highly effective components of disinfectants and antiseptics
• Halogens


  • Microbicidal and sporicidal with long exposure
• Chlorine 


  has been used as disinfectants & antisepsis for a long time.
• Chlorine 


  kills bacteria, endospores, fungi, viruses
• Chlorine


  Less effective if exposed to light, alkaline pH, and excess organic matter
• In solution, these compounds combine with water & release hypochlorous acid (HOCl) which oxidizes the sulfhydryl group on amino acid cysteine & interferes with disulfide bridges on numerous enzymes.


  The result is permanent denaturation of enzymes & suspends metabolic reactions.
• Hypochlorites: 


  • Broadly used in industry (sanitization & disinfection of food equipment in dairies, restaurants, treatment of swimming pools, spas, drinking water & fresh foods) and allied health (to treat wound, disinfect equipment, beddings, instruments)
• Household bleach is a weak solution of 5% sodium hypochlorite serves as all around disinfectant, deodorizer & stain remover.
• Chloramines (dichloramine, halazone): 


  • Used as alternatives to pure chlorine in water treatment due to its cancer-causing substances (trihalomethanes)
• Chloramines (dichloramine, halazone):


  Also serve as sanitizers and disinfectants, and for treating wounds and skin surfaces.
• Iodine and Its Compounds

  • Is a pungent chemical that forms brown-colored solution when dissolved in water or alcohol.
• • Iodine rapidly penetrates the cells of microorganisms where it disturbs metabolic function


  by interfering with hydrogen & disulfide bonding of protein
• All classes of organisms are killed by iodine if proper concentrations and exposure times are used
• Aqueous iodine • Contains 2% iodine and 2.4% sodium iodide

  • Used as topical antiseptic before surgery & occasionally as treatment for burn & infected skin
• Iodine tincture: • 2% of iodine & sodium iodide in 70% alcohol that can be used as skin antisepsis

  • 5%-7% aqueous solution and tincture of iodine can be extremely irritating and toxic when absorbed therefore unsafe for antisepsis
• Iodophors: • Complex of iodine and alcohol which allows slow release of free iodine & increases its degree of penetration.

  • Have replaced free iodine solutions in medical antisepsis because they are less prone to staining or irritating tissues.
• Iodophors:

  E.g. Betadine, Povidone & Isodine used to prepare skin and mucous membranes for surgery & injections, in surgical hand scrub, to treat burns, to disinfect equipment & surfaces