Download CHAPTER7 Microbial contamination

CHAPTER7
MICROBIAL CONTROL
Microbial contamination
• Sepsis refers to microbial contamination.
Also a term for blood infection/septicemia
• Asepsis is the absence of significant
contamination.
• Aseptic surgery techniques prevent
microbial contamination of wounds.
Terminology
• Bacteriostatic: inhibits bacterial growth
• Bactericidal: something capable of killing
bacteria
• Antiseptic: an agent that is used to inhibit/kill
bacterial growth on skin and mucus membranes
• Disinfectant: an agent that is used to inhibit/kill
bacterial growth on inanimate objects
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Terminology
• Sterilization: Removal of all microbial life
• Commercial Sterilization: Killing C. botulinum
endospores
• Degerming: Removal of microbes from a
limited area
• Sanitization: Lower microbial counts to safe
public health standards
• Biocide/Germicide: Kills microbes
History behind microbial control
• Joseph Lister was the
first to introduce the use
of carbolic acid to reduce
bacterial infections in
hospitals (1860s)
• Ignatz Semmelweis
regarded as the “Father
of Infection Control”,
physicians used
chlorinated lime to
cleanse hands (1850s)
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What factors influence the
success of microbial control?
• Is the organism an endospore former?
• What type of organism are you targeting?
• What type of environment are you
treating?
Bacteria die at a constant logarithmic rate
Figure 7.1a
Effectiveness of treatment
• Number of
microbes
• Environment
(organic
matter,
temperature,
biofilms)
• Time of
exposure
• Microbial
characteristic
Figure 7.1b
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Are all bacteria equally
sensitive?
What parts of a bacterial cell are
sensitive to physical treatments
and chemicals?
• Plasma membrane
• DNA and proteins
Physical Methods of Microbial
Control
• Heat
– Thermal death point (TDP): Lowest temperature
at which all cells in a culture are killed in 10 min.
– Thermal death time (TDT): Time to kill all cells in
a culture
– Decimal reduction time (DRT): Minutes to kill
90% of a population at a given temperature
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Physical Methods
• Heat
– Dry: kills by oxidation (incineration, flaming, hot air)
– Moist: promotes coagulation of proteins
• Boiling (100oC)
• Autoclave(121oC, 15lbs/sq inch)
• Pasteurization reduces spoilage organisms and pathogens
• Equivalent treatments
– Classic: 63°C for 30 min
– High-temperature short-time/HTST: 72°C for 15 sec
– Ultra-high-temperature/UHT: 140°C for <1 sec
– Thermoduric organisms survive
Autoclave
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Autoclaves work due to steam
under pressure
What if the substance is heat
labile?
• Filtration is the best
choice
• Pore sizes can be
either .45um or .22um
Physical Methods
• Low temperature: freezing does not kill bacteria,
most cultures are stored at -80oC
– Refrigeration (0⁰C to 7⁰C)reduces metabolic rate
– lyophilization
• High Pressure: apply to liquids such as fruit
juice; denatures proteins
• High Osmotic Pressure: use high concentration
of salt or sugar; plasmolysis
• Dessication: remove the water and bacteria can
remain viable but do not grow
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Physical Methods of Microbial
Control
• Radiation damages DNA
– Ionizing radiation (X rays, gamma rays, electron
beams)
– Nonionizing radiation (UV)
– (Microwaves kill by heat; not especially
antimicrobial)
Figure 7.5
Chemical Methods
• Most are only able to reduce the numbers of
organisms, not achieve sterility
• Types of chemicals
–
–
–
–
–
Phenol and phenolics
Halogens
Alcohols
Heavy metals
Soaps
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Chemical Methods of Microbial
Control
• Evaluating a disinfectant
– Use-dilution test
1.
2.
3.
Metal rings dipped in test bacteria are dried
Dried cultures placed in disinfectant for 10
min at 20°C
Rings transferred to culture media to
determine whether bacteria survived
treatment
Evaluation of chemicals: disc
diffusion method
• Phenol
• Phenolics
– coal tar (cresols)
– O-phenylphenol
(Lysol)
• Bisphenols.
Hexachlorophene
(Phisohex),
Triclosan
– Disrupt plasma
membranes
Figure 7.7
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Types of Disinfectants
• Biguanides. Chlorhexidine
– Disrupt plasma membranes
Chemical control
• Halogens
– Oxidizing agents
– Iodine
• Tincture
• Iodophor
• Skin disinfectant and wound treatment; some patients are
allergic to iodine
-Chlorine
Drinking water, swimming pools, etc.
Bleach is hypochlorous acid (HOCl)
Chloride dioxide-gas used for area disinfectant
Chemical Control
• Alcohols
– Mechanism of action is protein denaturation,
can also dissolve lipids
– Most common are ethanol and isopropanol
– Does not kill endospores or viruses
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Chemical control
• Heavy metals exert
oligodynamic action
• Denature proteins
• Silver, copper and
mercury
–
–
–
–
Silver nitrate: NBs
Silvadine: burns
Mercury: paints
Zinc: mouthwashes
Chemical control
• Surfactants (soaps)
– Little value as an antiseptic
• Acid-anionic surface-active sanitizers are
important in cleaning of dairy equipment
and utensils
• Quats: if foams, contains quats
– Mouthwashes
– Some bacteria (Pseudomonas) can grow
DISINFECTANTS
• Surface-action agents
or Surfactants
Soap
Degerming
Acid-anionic
Sanitizing
detergents
Bactericidal,
Quarternary
Denature
ammonium
proteins,
compounds
disrupt
Cationic
plasma
detergents
membrane
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Types of Disinfectants
• Chemical Food Preservatives
– Organic Acids
• Inhibit metabolism
• Sorbic acid, benzoic acid, calcium propionate
• Control molds and bacteria in foods and cosmetics
– Nitrite prevents endospore germination
– Antibiotics. Nisin and natamycin prevent
spoilage of cheese
Types of Disinfectants
• Aldehydes
– Inactivate proteins by cross-linking with
functional groups (–NH2, –OH, –COOH, —
SH)
– Glutaraldehyde: sterilizing, used on hospital
equipment
– Formaldehyde:preserve biological specimens
– Both used in embalming
Types of Disinfectants
• Gaseous Sterilants
– Denature proteins
– Ethylene oxide: Sterilizes; used to sterilize
spacecraft
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Types of Disinfectants
• Peroxygens
– Oxidizing agents
– O3, H2O2,
– peracetic acid (sterilize food processing and
medical equipment)
Are all bacteria equally
sensitive?
Which antiseptic works the
best?
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Microbial Characteristics and
Microbial Control
Chemical agent
Phenolics
Quats
Chlorines
Alcohols
Glutaraldehyde
Effectiveness against
Endospores Mycobacteria
Poor
Good
None
None
Fair
Fair
Poor
Good
Fair
Good
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