Transcript Control of Microbial Growth (Sterilization and

Control of Microbial Growth
(Sterilization and Disinfection)
Control of Microbial Growth
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Microbial Control

Can inhibit growth of
many microorganisms
by washing and
scrubbing with soaps
and detergents.
www.enviroblog.org
Sterilization

Process of removing
or killing all
microorganisms and
viruses on or in a
product.
– Ensures complete
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destruction of all
microorganisms,
including cells, spores,
and viruses.
www.medicalcareerinstitute.net
Examples of Sterilization

Dry heat
 Autoclaving
 Gas
 Various chemicals
 Certain types of
radiation
Autoclave. www.lifelinemedical.net
Dry Heat Sterilization. www.kabdental.com
Disinfection

Process that reduces # of
potential disease-causing
bacteria and viruses on a
material until they no longer
present a hazard.

Terms decontamination and
sanitation mean the same thing
generally.

Disinfectant
– A chemical used to disinfect
inanimate objects.
Example of Disinfection Pasteurization

Method of
disinfecting liquids.

Heat liquids to a
certain temperature.

Does not totally
destroy pathogens.
Pasteurization Equipment.
www.foodprocessing-technology.com
Decontamination

Inactivation or removal of both microbial
toxins and the living microbial pathogens.
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Antiseptic

Solutions used to
disinfect skin and
other living tissues.
www.firstaid-direct.co.uk
Sanitation

Reduction of
microbial populations
to levels considered
safe by public health
standards.
www.zerrenterprises.com
Microbicidal Agents

The suffix –cide or –cidal refers to
“killing.”
– Ex. Microbicidal agents (microbicides)
– Ex. Bactericidal agents
– Ex. Sporicidal agents
– Ex. Viricidal agents
Microbistatic Agents

Microbistatic Agent


Bacteriostatic Agent


Drug or chemical that inhibits the growth and
reproduction of microorganisms.
One that specifically inhibits the metabolism and
reproduction of bacteria.
Microbistatic technique examples


Ex. Lyophilization (freeze-drying)
Ex. Rapid freezing (using liquid nitrogen)
Some Useful Terms

Sepsis


Asepsis



Absence of pathogens.
Ex. Hand washing; use of sterile
gloves, masks, gowns; sterilization
of surgical equipment; use of
disinfectants.
Antisepsis


Presence of pathogens in blood or
tissues.
Prevention of infection.
Antiseptic technique


Developed by Joseph Lister
(1867).
Use of antiseptics.
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Sterile Technique

Practice of excluding all microorganisms
from a particular area, so that the area will
be sterile.
bioweb.wku.edu
Controlling Microbial Growth
Using Physical Methods

Methods used to destroy or inhibit microbial
growth may be physical or chemical.
 Examples:
Heat
 Combination of heat and pressure
 Desiccation
 Radiation
 Sonic disruption
 Filtration

Heat

Practical, efficient, and inexpensive method of
sterilization.

2 factors that influence effectiveness of heat for
sterilization: temperature and time
– Thermal Death Point (TDP)
Lowest temperature that will kill all organisms in a
standardized pure culture within a specified period.
– Thermal Death Time (TDT)
 Length of time necessary to sterilize a pure culture at a specified

temperature.
Dry Heat

Heating materials in absence
of moisture.

Must be baked at 160º to
165ºC for 2 hours or at 170º
to 180ºC for 1 hour.

Other methods include
incineration and flaming
surface of metal materials
like forceps and loops.
biology.clc.uc.edu
Moist Heat

Boiling or steaming.

Most pathogens destroyed
after 30 minutes of
boiling.

Boiling not always
effective against some
endospores and viruses.

Boiling not an option for
thermophiles.
Boiling. ttt.astro.su.se
Steamer. www.appliancist.com
Autoclaving

Large metal pressure
cooker that uses steam
under pressure to
completely destroy all
microorganisms.

Increased pressure
raises the temperature
of boiling water (i.e.
above 100ºC)
producing steam.
www.uwm.edu
Home Canning

Use of a pressure
cooker.

If foods canned
without pressure some
bacterial endospores
may survive.

www.thecookwarebarn.com
i.e. Clostridium
botulinum
Bulging lid – botulism.
calorielab.com
Disinfecting Techniques

For clothing, bedding,
and dishes

Use hot water with soap
or detergent

Agitate solution around
items

Combination of heat,
mechanical action, and
chemical inhibition kills
most microbes.
Washing Machine.
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Cold

Metabolic activities slowed.

Most microbes not killed, but
growth inhibited.
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
Slow freezing not a good way
to preserve bacteriological or
biologic specimen.

Rapid freezing (liquid nitrogen)
good for this.

Why should you not refreeze
foods?
Slow Freezing.
Rapid Freezing –
liquid nitrogen.
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Desiccation

Process of drying materials.

Many microbes can remain
viable despite absence of
nutrients and moisture.

Ex. Lyophilization (freezedrying)

Dried blood, fecal material, and
dust may still contain viable
microbes.
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Radiation

Ultraviolet (UV) light sometimes used to
prevent or decrease microbial growth.
 X-rays and gamma and beta rays may be
used to destroy or prevent microbial growth.
www.fda.gov
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Ultrasonic Waves

Often used to sterilize and clean delicate equipment.

Consists of tanks filled with liquid solvent (usually
water).

Short sound waves are passed through liquid.

Sound waves dislodge organic debris.

Materials must then be washed and sterilized by
another method.
Filtration


Filters of various pore sizes are
used to filter or separate larger
cells, larger viruses, bacteria,
and other microbes from gases
or liquids in which they are
suspended.
wps.prenhall.com
Paper masks used to prevent the
outward and inward movement
of microbes.
health.howstuffworks.com
Gaseous Atmosphere

Altering atmosphere of microbes to inhibit
growth.
Hyperbaric Chamber.
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Gas gangrene – caused
by Clostridium spp.
www.humanillnesses.com
Chemical Agents Used to Inhibit
Microbial Growth

Temporarily or permanently.

Different disinfectants have different
properties.

Disinfectants should be chosen based on
their efficiency and effectiveness for a
particular situation.
What Are Some Things to
Consider When Choosing a
Chemical Disinfectant?
What makes an Ideal Chemical
Antimicrobial Agent?
How Do Disinfectants Kill
Microorganisms?

Some target and destroy cell membranes.


Some destroy enzymes and structural proteins.


Ex. Surface-active soaps and detergents; alcohols
Ex. Formaldehyde and ethylene oxide
Some attack cell walls or nucleic acids.
Antiseptics

Can be used safely on
human skin.

Reduces # of organisms
on the surface.
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
Does not penetrate pores
or hair follicles.
Preventing Growth of Pathogens
in Our Kitchens
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The Antibiotic Controversy
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The End