Microbiology: Principles and Explorations

Sixth Edition

Chapter 12:Sterilization and Disinfection

Copyright © 2005 by John Wiley & Sons, Inc.

Jacquelyn G. Black

Principles of Sterilization and Disinfection

• Disinfectant: Typically chemical agents that are applied to inanimate objects

• Antiseptics: Typically chemical agents that are applied to living tissues

• Table 12.1

• Sterilization: The killing or removal of all living cells, viable spores, viruses in a material or on an object

• Sterility: there are no living organisms in or on an object

• Disinfection: The reduction of the number of pathogenic microorganisms to the point that they pose no danger of disease

Disinfectant and Antiseptic Response of Staphylococcus aureus

Disinfectant and Antiseptic Response of Escherichia coli

Denaturing Proteins

Action of a Surfactant

Structural Formulas of Common Disinfectants

Heavy Metal Effect on Bacterial Growth

Biodecontamination Unit—Hydrogen

Peroxide

Biodecontamination Unit—Ethylene

Oxide

Sterilization—Hot Air Oven

Small Countertop Autoclave

Model Autoclave

• X rays and gamma rays are forms of ionizing radiation

• So named because it can dislodge electrons from atoms creating ions

• Damages DNA and produces peroxides (powerful oxidizing agents in cells)

• Deinococcus radiodurans: Able to survive 1000X the amount of radiation that would kill a human (bioremediation of radioactive contaminated sites)

Ionizing Radiation

• If water is heated under pressure, its boiling point is elevated, so temperatures above 100oC can be reached

• Pressure: 15 lbs per square inch (psi)

• 15 – 20 minutes at 121oC

• Prions are highly resistant and must be sterilized longer and at higher temperature (134oC for 18 min)

Autoclaving

Checking for Sterility

Pasteurization

• A process invented by Pasteur to destroy microbes that caused wine to sour, does not achieve sterility

• Kills pathogens: Salmonella and Mycobacterium

• Milk is pasteurized by heating it to 71.6oC for at least 15 seconds (flash method)

• Milk is pasteurized by heating it to 62.9oC for 30 minutes (holding method)

Large Automatic Hospital Autoclave

Preservation by Drying

Lyophilization—Stoppering Tray Dryer

Lyophilization—Manifold Dryer

• A definite proportion of the organisms die in a given time interval

• The fewer organisms present, the shorter the time needed to achieve sterility

• Microorganisms differ in their susceptibility to antimicrobial agents

• The most susceptible phase for most organisms is the logarithmic growth phase

The Control of Microbial Growth

• Germicide: An agent capable of killing pathogens and nonpathogens but not necessarily endospores

• Bacteriostatic agent: An agent that inhibits the growth of bacteria

1. Bactericide

2. Bacteriostatic

The Use of Physical Methods in Control of Microbial Growth

• Heat and other physical agents are normally used to control microbial growth and sterilize objects:

1. Heat2. Low Temperatures3. Filtration4. Radiation

Heat• One of the most popular ways to destroy

microbes (flame or boiling)

• Moist or Dry heat may be used

• Exposure to boiling water for 10 minutes is sufficient to destroy vegetative cells and eukaryotic spores

• Steam sterilization (autoclaving) is necessary to destroy the bacterial endospore

Radiation

• Ultraviolet radiation (260nm): is quite lethal in destroying microbes but it does not penetrate glass, dirt films, or water

• Ionizing radiation (IR): An excellent sterilizing agent because of its ability to penetrate deep into objects

• IR will destroy bacterial endospores and both prokaryotic and eukaryotic vegetative cells

UV Radiation—Serratia marcescens

Microwave Sterilization

Filtration Sterilization

Filtration

• Can be used to sterilize substances that are destroyed by heat (drugs, serum, vitamins, sucrose)

• To separate viruses from bacteria (manufacture of vaccines)

• To collect microorganisms from air and water samples (water quality testing)

Staphylococcus epidermidis on surface of 0.22m Millipore Membrane Filter