CONTROL OF MICROORGANISMS

I.  Introduction

    A.  Sterilization

        aseptic
 

    B.  Disinfection

        1. Disinfectant
 

        2.  Antiseptic
 

        3. Sanitation
 
 

    C.  -cidal, -static, and -lytic (suffixes)

        -cidal

        -static

        -lytic
 

    D.  Pyrogen free
 
 

II.  Pattern of Microbial Death
 
 
 

III.  Factors Influencing Microbial killing

    A.  Type of M.O. present and physiologic state

       

    B.  Number of M.O.
 
 

    C.  Type of Control Agent and Concentration
 
 

    D.  Length of Exposure Time
 
 

    E.  Temperature
 
 

    F.  Type of Environment

        presence of extraneous material interferes with contact

        organic compounds

        pH
 

IV.  General Sites of Action of Antimicrobial Agents

    A.  Cell membranes

        1.  altered permeability

        2.   decrease active transport activity
 

    B.  Proteins

        denature
 

    C.  Nucleic acids
 

V.  Physical Methods of Control

    A.  Heat

        two important factors:  time and temperature

        TDT

        F-value

        1.  Dry Heat

            a) direct flaming (incineration)
 

            b) hot air sterilization

                160-180C, minimum 2 hrs

        2.  Moist heat

            a)  boiling
 

            b)  fractional sterilization (Tyndalization)
 

            c)  autoclaving

                15 lbs of pressure, 1210C
 

            d)  pasteurization

                does not sterilize

                originally 65C for 30 min.

                flash pasteurization: 71.70C for 15 sec
 

    B.  Cold

            bacteriostatic
 

    C.  Dessication

            bacteriostatic

            lyophilization
 

    D.  Irradiation

        1. Ionizing radiation

            short wavelength, high energy

            disadvantages
 

        2.  Non-ionizing

            longer wavelength, lower energy

            disadvantages
 

VI.  Mechanical Methods of Control

  1. sterilize liquids and air


  2. disadvantages
     

VII.  Chemical Methods of Control

    A. Phenols

        1. carbolic acid

            phenol coefficient (comparison)

        2.  Phenolics

            examples: Cresol, Lysol, Amphyl, Hexochlorophene (Phisohex), Phisoderm-octoxynol, tricolsan
 

    B.  Heavy Metals

        silver, mercury

        examples: 1% AgNO3, mercury, zinc, H2O2, CuSO4
 

    C. Halogens

        1. Iodine

            tincture

            iodophor
 

        2. Chlorine

            a)  water treatment
 

            b)  hypochlorite (bleach)
 
 

    D. Quaternary Ammonium Compounds (Quats)

          relatively mild
 

    E. Alcohols

        bactericidal

        requires water to denature proteins
 

    F. Acids and alkalis

        denatures proteins

        examples: boric acid, sorbic acid, benzoic acid, Desenex, parabens
 

    G. Aldehydes

        1. Formaldehyde

            toxic

            Formalin
 

        2. Gluteraldehyde

            Cidex
 

    H. Ethylene Oxide and Propyline Oxide

        gases

        toxic and flammable
 

    I. Oxidizing agents

        examples: H2O2 , ozone (O3)
 

VII. Summary

    A.  Preservation of food

          1.  temperature

          2.  organic acids

          3.  parabens

          4.  sulfites

          5.  nitrites

          6. bacteriocins

          7. bacteriophages

          8.  high pressure processing

 

      B.  Selection of compound


       C.  Classification of germicides based on effectiveness
 
 

Last updated July 2, 2009.