Chapter 13: Control of Microbial Growth

Disinfection

The destruction or removal of vegetative pathogens but not bacterial endospores. Usually used only on inanimate objects.

• Boiling water, hot water, pasteurization

• Radiation; Non-ionizing, UV

• Chemical gases

• Air filtration

• Chemical liquids on inanimate objects

Sterilization

The complete removal or destruction of all viable microorganisms. Used on inanimate objects.

• Incineration

• Dry oven

• Filtration of liquids

• Chemical Gases

• Chemical liquids on inanimate objects

Antisepsis

Chemicals applied to body surfaces to destroy or inhibit vegetative pathogens

• Chemical liquids on animate objects

Microbial Death

The permanent loss of a microorganism’s ability to reproduce. It can occur when a microorganism stops moving, metabolizing, or reproducing.

Antimicrobial Agents Modes of Action

Cellular targets of physical and chemical agents.

• Cell wall

• Cell membrane

• Protein and nucleic acid synthesis

• Proteins

Methods of Physical Control

1. Heat - moist and dry

2. Cold temps

3. Desiccation

4. Radiation

5. Filtration

Desiccation

Method of microbial control involving the removal of water from cells through drying or dehydration.

• Not effective in microbial control

Moist Heat

A method of microbial control that involves using water and heat, such as boiling, autoclaving, pasteurization, unpressurized steam, steam under pressure.

Dry Heat

A microbial control method that uses hot air to sterilize items

• Denatures proteins and alters membranes, dehydration, desiccation.

Thermal death time

Shortest length of time required to kill ALL test microbes at a specified temperature.

Thermal death point

Lowest temperature required to kill ALL microbes in a sample for 10 mins.

Autoclave

Specialized device for the moist-heat sterilization of materials through the application of pressure to steam, allowing the steam to reach temperatures above the boiling point of water.

• Denatures proteins and alters membranes

Microbiostatic

Slows the growth of microbes

• Refrigeration

• Freezing

Lyophilization

Freeze drying; preservation.

• Inhibits metabolism

Ionizing radiation

Deep penetrating power breaks DNA

• Gamma rays, x-rays, cathode rays.

Alters molecular structures, introduces double-strand breaks into DNA

Nonionizing radiation

Little penetrating power so it must be directly exposed.

• UV light creates pyrimidine (thymine) dimers, which interfere with replication

Introduces thymine dimers, leading to mutations

Filtration

Physical removal of microbes by passing gas or liquids through the filter

• Heat sensitive liquids.

• Air (HEPA filters)

Physically removes microbes from air/liquid

High level germicides

Kill endospores; may be sterilant

• Devices that are not heat sterilizable and intended to be used in sterile environments (body tissue)

Intermediate level

Kill fungal spores (not endospores), resistant pathogens (i.e. tubercle bacillus) and viruses.

• Devices that will come in contact with mucous membranes but are not invasive.

Low level

Eliminate only vegetative bacteria, vegetative bacteria fungal cells, and some viruses.

• Clean surfaces that touch skin but not mucous membranes.