This is chapter 8 -Control of Microorganisms in the Environment detailed notes. If you want to skip reading the entire chapter in the textbook and just memorize the necessary information for the chapter, consider purchasing this study guide!
Microbiology
Chapter 8 - Control of Microorganisms in the Environment
8.1 : Microbial Growth and Replication: Targets for Control
Biocide: All antimicrobial agents that can be used to control microorganisms.
Controlling Microorganisms
* Physical, Chemical, and mechanical methods to destroy or reduce undesirable mi-
crobes in a given area. (Decontamination)
* Primary targets are microorganisms capable of causing infection or spoilage.
Highest Resistance
- Prions and bacterial endospores
Least Resistance
- Most bacterial vegetative cells
- Fungal spores and hyphae yeast
- Enveloped viruses
- Protozoan trophozoites
Terminology and Methods of Control
For Animate Objects:
Antisepsis: destruction or inhibition of microorganisms on living tissue. (Prevention
of infection of living tissue by microorganisms or sepsis)
, Antiseptics: Chemical agents applied to tissue to prevent infection by killing or in-
hibiting pathogen growth ; they also reduce the total microbial population.
* Antiseptics are not as toxic as disinfectants because they can’t cause too much
harm to the host.
Chemotherapy: Application of chemicals to kill or inhibit the growth of microorgan-
isms.
* Chemotherapeutic agents are often characterized by the outcome of their applica-
tion.
- A disinfectant or antiseptic can be particularly effective against a specific group
and may be called bactericide, fungicide, or viricide.
- Some chemicals do not kill, but prevent further growth. If chemicals are removed,
growth will resume. This is called Bacteriostatic / Fungistatic.
The Pattern of Microbial Death Mirrors the Pattern of Microbial
Growth
- One measure of an agent’s killing efficiency is the Decimal Reduction Time (D)
/ D Value: this time is required to kill 90% of the microorganisms or endospores
in a sample under specified conditions.
(I.e): in a semilogarithmic plot of the population remaining vs. the time of heating,
the D value is the time required for the line to drop by one log cycle or 10-fold.
* To study the effectiveness of a lethal agent, one must be able to decide when a
microorganisms are dead which may present some challenges.
* Microbial cells are defined as dead if they don’t grow when inoculated into culture
medium that would normally support it’s growth. Similarly, an inactive virus can-
not infect a suitable host.
8.2: Microbes Can Be Controlled By Physical Means
Filtration: Excellent way to reduce the microbial population in solutions of heat
sensitive materials and can be used to sterilize liquids and gases (including air).
* There are two types of liquid filtration systems.
1) Depth Filters: Consist of fibrous or granular materials that have been bonded
into a thick layer filled with narrow twisting channels.
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