Download Chapter 5 Control of Microbial growth

Chapter 5; Control of Microbial
growth
Bio 261
Medgar Evers College
Prof. Santos
Terms and definitions
• Sterilization- the process of removing
completely all microorganisms on or in a
product
• Sterile item- is free of microbes including
endospores and viruses.
• Disinfection- the removal of most or all
pathogens on or in a material. Generally
implies the use of an antimicrobial
chemical.
• Disinfectants- antimicrobial chemicals
used on inanimate objects. They can also
be called germicides because they target
bacteria, viruses, fungi and endospores.
• Bactericidal- these target bacteria
• Antiseptics- a disinfectant that is
formulated for use on the skin.
• Pasteurization- brief heat treatment to
reduce the number of spoilage organisms
Deciding which method of control
to use!
• This depends on several factors!!
• These factors include the situation and
degree of control needed!
SITUATIONS!
1- Daily life
2-Hospitals
3-Microbiology laboratory
4-food and food product facilities
5-Water treatment facilities (chlorine and
consequence of disinfectant by products)
Factors that affect our selection of
an antimicrobial procedure
1- type of microorganism present. The
following organisms require special
consideration due to high resistance;
bacterial endospores, protozoan cysts and
oocytes, mycobacterium species,
pseudomonas species, naked viruses.
2 - number of microorganisms initially
present.
In the canning process the decimal
reduction time or D value is the time
required for killing 90% of a population of
bacteria under certain conditions. A one D
process reduces the number of organisms
by one exponent.
Example; Let’s say the D value of a certain
organism is 2 minutes (D=2).
Let’s say the initial number of cells is 103, it
would take 6 minutes to go down to 100 or 1
survivor!
3- environmental conditions such as pH,
temp, organic materials, and presence of
fat greatly influence the rate microbial
growth.
4- potential risk of infection
Instruments are classified as
1. critical instruments (needles, scalpels,
biopsy forceps)
2. semicritical instruments (endoscopes,
endotracheal tubes.
3. noncritical instruments (stethoscopes
and blood pressure cuffs.
Potential risk of infection
Critical items come into direct contact with body tissues.
1. _______
Surgical instruments
Biopsy forceps
needles
Semicritical
2. ____________
items come into contact with mucous membranes,
but do not penetrate body tissues.
Respiratory equipment
Vaginal
speculum
Anal proctoscope
Noncritical items only touch keratinized skin surfaces.
3. ____________
Sphygmomanometer
(blood pressure cuff)
stethoscope
5- composition of item
• Based on the composition of the item to be
sterilized, an appropriate sterilization method
must be chosen. Certain plastics are heat
sensitive so they must be treated with an
antimicrobial chemical agent or it can be
irradiated.
• Some moisture sensitive material can’t be
treated with chemicals so they can be heat
treated.
Processes used to control
microorganisms
• These can be either physical or chemical!
Physical methods!
1- Moist heat- denatures proteins, its safe,
fast and inexpensive
2- Dry heat
3- Filtration
4- Radiation
5- High pressure
Moist heat
a) Boiling destroys most bacteria, viruses,
but not endospores. Boiling for at least
five minutes can be used to sterilize
drinking water.
b) Pasteurization- decreases the number of
heat sensitive microorganisms except
spore formers. Widely used to treat milk
and some juices. 72 degrees for 15 secs.
Two types of pasteurization;
1-High temp short time method (HTST)
2-Ultra high temp (UHT) method. This
method usually employs 140-150 degrees
for several seconds and then rapidly
cooled. The products are then transferred
to chemically treated containers.
Examples would be boxed juices and
boxed milks.
Pasteurization a brief heat treatment followed by rapid cooling.
b. ____________:
(Kills pathogens and reduces the number of spoilage organisms in
milk, juices, wine, beer: Does not sterilize!)
(1). LTLT (Low Temperature Long Term) 63°C/30 minutes
*(2). HTST (High Temperature Short Term) 72°C/15 seconds
Autoclave (steam under pressure)
_________
(1). 15-20 psi/15-20 minutes/121°C
Sterilizes equipment, media, etc.
(2). ________
(3). used in canning procedures to destroy
endospores
Clostridium botulinum __________!
c) Pressurized steam (autoclaving)
typical treatment is 121 degrees
Celsius/15 PSI (pounds per square inch)
for fifteen minutes.
Flash autoclaving
Rapid autoclaving (3 mins or so) at a high
temperature of 135 degrees C.
Dry heat
a) incineration- oxidizes cell components to
ashes
b) dry heat oven- oxidizes cell components
and denatures proteins.
*Dry heat is less efficient due to a higher
temp that is required and longer time
needed.
Filtration
a) liquid filtration using a membrane filter. A
liquid is passed through a filter with pores
that trap microbes.
b) HEPA filters used to filter air and trap
organisms larger than .3 um in diameter.
Radiation
a) Ionizing radiation includes gamma rays
and x rays. These destroy DNA and
possibly damages cell cytoplasmic
membranes. Reactive molecules that
damage cell components are produced!
*used to sterilize drugs, medical equipment,
and disposable surgical supplies.
b) UV damages DNA but penetrates poorly.
Used to disinfect air, drinking water, and
large surfaces and destroy microbes in
spices.
High Pressure
• Pressure of over 130,000psi.
• It denatures proteins, and alters the
permeability of the cell.
• Used for commercial food products.
Chemical methods!
Classes of chemicals used!
1-alcohol aqueous solutions.
2-aldehydes
3-Biquanides
4-ethylene oxide gas
5-halogens
6-metals
7-ozone
8-peroxygens
9-phenolic compounds
10-quaternary ammonium compounds
Target zone
I. Cell membrane
1.Quats
2.Biguanides
3.Phenolics
II. Proteins
1.Alcohols
2.Aldehydes
3.Metals
4.Halogens
5.Peroxygens
6.Phenolics
7.Ozone
III. DNA
1.Ethylene oxide gas
2.Aldehydes
Uses of each chemical method
1- alcohol, aqueous solutions are used to
degerm skin and disinfect instruments.
2- aldehydes, used as preserve biological
specimens, sterilize medical equipment,
and formalin is used in vaccine production.
3- Biguanides are used as antiseptics in
soap and lotions and impregnated into
catheters and surgical mesh.
• Example; chlorhexidine
4- ethylene oxide gas is used to sterilize
medical devices.
5- halogens such as solutions of chlorine are
used to disinfect inanimate objects,
surfaces, waste water and drinking water.
6- metals are used in topical dressing to
prevent infection.
7- Ozone is used to disinfect waste water
and drinking water
8- peroxides are used to sterilize containers
for juices and milk and disinfect medical
devices.
9-phenolic compounds are found in a variety
of personal care products such as
toothpaste, lotions, and deodorant soaps.
Example; Triclosan in toothpaste, lotions
and soaps
Example; Hexachlorophene (nabac) is
potent against S. aureus but causes nerve
damage
10- Quaternary ammonium compounds are
used to disinfect inanimate objects and
preserve nonfood substances.
These are cationic detergents that reacts
with membranes destroying vegetative
cells and envelope viruses.
Preserving perishables
• Chemical
• Low temp storage such as refrigeration
and freezing
• Reducing the amount of water by using
salt.
Chemical preservatives
• Examples are benzoic acid, sorbic acid,
propionic acid, quaternary ammonium
compounds, thimerosal, nitrate, and nitrite.