Chemical Methods of Microbial Control

• Chemical Methods of Microbial Control

  • Affect microbes' cell walls, cytoplasmic membranes, proteins, or DNA
  • Effect varies with temperature, length of exposure, and amount of organic matter
  • Also varies with pH, concentration, and age of chemical
  • Tend to be more effective against enveloped viruses and vegetative cells of bacteria, fungi, and protozoa
• Phenol and Phenolics


  • Level of Activity: Intermediate to Low
  • Action: Denatures proteins and disrupts cell membranes
  • Effective in the presence of organic matter and remains active for a prolonged time
  • Commonly used in health care settings, labs, and homes (Lysol, triclosan)
  • Have disagreeable odor and possible side effects
• Alcohols


  • Level of Activity: Intermediate
  • Action: Denature proteins and disrupt cytoplasmic membranes
  • Evaporate rapidly – both advantageous and disadvantageous
  • Swabbing of skin with 70% ethanol before injection
• Halogens


  • Level of activity: Intermediate
  • Action: Denature Proteins
  • Examples: Iodine tablets, iodophores (Betadine®), chlorine treatment of drinking water, bleach, chloramines in wound dressings, and bromine disinfection of hot tubs
• Oxidizing Agents


  • Level of activity: High disinfectants and antiseptics
  • Action: Denature proteins by oxidation of microbial enzymes
  • Examples:Peroxides, ozone, and peracetic acid
  • Hydrogen peroxide can disinfect and sterilize surfaces of objects
  • Catalase neutralizes; not useful for treating open wounds
  • Ozone treatment of drinking water
  • Peracetic acid – effective sporocide used to sterilize equipment
• Surfactants


  • Level of activity: Low
  • Action: Decrease surface tension of water and disrupt cell membranes
  • "Surface active" chemicals that reduce the surface tension of solvents to make them more effective at dissolving solutes
  • Example: Soaps and detergents
  • Soaps have hydrophilic and hydrophobic ends; good degerming agents but not antimicrobial
  • Detergents are positively charged organic surfactants
  • Quats – colorless, tasteless, harmless to humans, and antimicrobial; ideal for many medical and industrial application
• Heavy Metals


  • Level of activity: Low bacteriostatic and fungistatic agents
  • Action:Denature Proteins
  • Ions are antimicrobial because they alter the 3-D shape of proteins, inhibiting or eliminating their function
  • 1% silver nitrate to prevent blindness caused by N. gonorrhoeae
  • Thimerosal used to preserve vaccines
  • Copper controls algal growth in reservoirs, fish tanks, swimming pools, and water storage tanks; interferes with chlorophyll
• Aldehydes


  • Level of activity: High
  • Action: Denature Proteins
  • Compounds containing terminal –CHO groups
  • Cross-link with amino, hydroxyl, sulfhydryl, and carboxyl groups to denature proteins and inactivate nucleic acids
  • Glutaraldehyde both disinfects (short exposure) and sterilizes (long exposure)
  • Formalin is used in embalming and disinfection of rooms and instruments
• Gaseous Agents


  • Level of activity: High
  • Action: Denature proteins and DNA by cross-linking functional groups
  • Ethylene oxide, propylene oxide, and beta-propiolactone used in closed chambers to sterilize items
  • Used in hospitals and dental offices
  • Can be hazardous to people, often highly explosive, extremely poisonous, and potentially carcinogenic
• Enzymes


  • Level of activity: High against target substrate
  • Action: Denature proteins
  • Antimicrobial enzymes act against microorganisms
  • Human tears contain lysozyme, which digests the peptidoglycan cell wall of bacteria
  • Scientists are looking for ways to use enzymes to control microbes in the environment
  • Lysozyme is used to reduce the number of bacteria in cheese
  • Prionzyme can remove prions on medical instruments
• Antimicrobials


  • Level of activity: Intermediate to Low
  • Action: Act against cell walls, cell membrane, protein synthesis, and DNA transcription and replication
  • Example: Antibiotics, semi-synthetic, and synthetic chemicals
  • Typically used for the treatment of disease
  • Some are used for antimicrobial control outside the body
• Development of Resistant Microbes:

  • Little evidence that extensive use of products containing antiseptic and disinfecting chemicals adds to human or animal health
  • The use of such products promotes the development of resistant microbes