Quick Revision: Sterlization & Disinfection


A. Definations.

  1. Sterility—total absence of viable microorganisms as assessed by no growth on any medium.
  2. Bactericidal—kills bacteria.
  3. Bacteriostatic—inhibits growth of bacteria.
  4. Sterilization—removal or killing of all microorganisms.
  5. Disinfection—removal or killing of disease-causing microorganisms.
  6. Sepsis—infection/ infected with microorganism.
  7. Antisepsis—any procedure that inhibits the growth and multiplication of microorganisms.

B. Methods

  1. Moist heat (autoclaving at 121°C/250°F for 15 minutes at a steam pressure of 10.55 kg/m2  (15 pounds per square inch) kills microorganisms, including endospores.
  2. Dry heat and incineration are both methods that oxidize proteins, killing bacteria.
  3. Ultraviolet radiation blocks DNA replication.
  4. Chemicals:
    a. Phenol is used as a disinfectant standard that is expressed as a phenol coefficient, which compares the rate of the minimal sterilizing concentration of phenol to that of the test compound for a particular organism.
    b. Chlorhexidine is a diphenyl cationic analog that is a useful topical disinfectant.
    c. Iodine is bactericidal in a 2% solution of aqueous alcohol containing potassium iodide. It acts as an oxidizing agent and combines irreversibly with proteins. It can cause hypersensitivity reactions.
    d. Chlorine inactivates bacteria and most viruses by oxidizing free sulfhydryl groups.
    e. Quaternary ammonium compounds (e.g., benzalkonium chloride ) inactivate bacteria by their hydrophobic and lipophilic groups, interacting with the cell membrane to alter metabolic properties and permeability.
    f. Ethylene oxide is an alkylating agent that is especially useful for sterilizing heat-sensitive
    hospital instruments. It requires exposure times of 4 to 6 hours, followed by aeration to
    remove absorbed gas.
    g. Alcohol requires concentrations of 70% to 95% to kill bacteria given sufficient time.

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