Download Using Chemicals to Destroy Microorganisms and Viruses

Control of Microbial Growth
Chapter 5
• Why do we need to control bacteria
growth? To what degree?
• How do we control bacteria growth?
• Daily life
• Hospital
• Microbiology lab
• Food facilities
• Water facilities
Approaches to Control
• Control mechanisms either physical or
chemical (or both)
– Physical methods
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Heat
Irradiation
Filtration
Mechanical removal
– Chemical methods
• Use a variety of antimicrobial chemicals
• Chemical depends on circumstances and degree
of control required
Approaches to Control
• Degree of control
– Sterilization
– Disinfection
– Pasteurization
Selection of Antimicrobial
Procedure
• Choice of procedure depends on
numerous factors
Situational considerations
Type of microbe
Extent of contamination
Number of organisms
Environment
Risk of infection
Composition of infected item
Selection of Antimicrobial
Procedure
• Type of microorganism
– resistant microbes
• Endospores
• Protozoan cysts and oocysts
• Mycobacterium species
• Pseudomonas species
• Naked viruses
Selection of Antimicrobial
Procedure
• Number of organisms
initially present
– Time it takes to kill depends
on population size
– decimal reduction time
• A.k.a D value
• Washing effect
Quiz
• If the D value is 3 min, how long does it
take to reduce 10,000 to 1?
Selection of Antimicrobial
Procedure
• Environmental conditions
– Environmental conditions strongly influence
effectiveness
• pH, temperature and presence of organic materials
affect effectiveness
Selection of Antimicrobial
Procedure
• Potential risk of infection
– Medical items categorized according to
potential risk of disease transmission
• Critical items
• Semicritical instruments
• Non-critical instruments
Selection of Antimicrobial
Procedure
• Composition of the item
– Some sterilization and disinfection methods
inappropriate for certain items
• Heat inappropriate for plastics and other heat
sensitive items
Physical control--Heat
• Heat treatment most useful for microbial
control
• Heat can be used to sterilize or disinfect
• Methods include
– Moist heat
– Dry heat
Heat as Control
• Moist heat
– mechanism
– Moist heat includes
• Boiling
• Pasteurization
• Pressurized steam
Heat as Control
• Boiling (100 C)
– Destroys most microorganisms and viruses
– Not effective means of sterilization
• Pasteurization
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Pasteur developed to avoid spoilage of wine
significantly reduces organisms
increase shelf life of food
Heated to 72°C and held for 15 seconds
Other protocol UHT
• Heated to 140°C - 150°C, held for several seconds then
rapidly cooled
Heat as Control
• Pressurized steam
– Autoclave used to sterilize
using pressurized steam
– Achieves sterilization at
121°C and 15psi in 15
minutes
• Prions destroyed at 132°C
and 15psi for 4.5 hours
Heat as Control
• Dry heat
– Not as effective as moist heat
– 200°C for 1.5 hours vs. 121°C for 15 minutes
– Incineration method of dry heat sterilization
• Flaming laboratory inoculation loop incinerates
organism
Control of bacteria growth--physical method
• Low temperature storage
– Microbial growth is temperature dependent
– Freezing means of food preservation
• Essentially stops microbial growth
• Irreversibly damages cell
Other Physical Methods
of Control
• Heat sensitive materials require other
methods of microbial control
– Filtration
– Irradiation
– High-pressure treatment
Other Physical Methods
of Control
• Filtration
– Membrane filtration
used to remove
microbes from fluids
and air
– Liquid filtration
• Heath sensitive
– Filtration of air
• High efficiency
particulate air (HEPA)
filter remove nearly all
microbes from air
Other Physical Methods
of Control
• Radiation
– Electromagnetic radiation
• Energy released from
waves
• Range of wavelength is
electromagnetic spectrum
• Radiation can be ionizing or
non-ionizing
Other Physical Methods
of Control
• Ionizing radiation
– Radiation able to strip electrons from atoms
– Three sources
• Gamma radiation
• X-rays
• Electron accelerators
– mechanism
– Used to sterilize heat resistant materials
• Medical equipment, surgical supplies, medications
• Some endospores can be resistant
Other Physical Methods
of Control
• Ultraviolet radiation
– Non-ionizing radiation
• Damages DNA
– Used to destroy microbes in air, drinking
water and surfaces
– Limitation
• Poor penetrating power
Chemicals as Control
• Chemicals can be
used to disinfect and
sterilize
– Called germicidal
chemicals
• Reacts with vital cell
sites
– Proteins
– DNA
– Cell membrane
Chemicals as Control
• Potency of chemicals
– Formulations generally
contain more than one
antimicrobial agent
– Regulated by
• FDA
– Antiseptics
• EPA
– Disinfectants
– Germicidal agents grouped
according to potency
• Sterilants =
– Destroy all microorganisms
• High-level disinfectants
– Destroys viruses and vegetative
cells,
– Not endospores
• Intermediate-level disinfectants
– Kills vegetative cells fungi, most
viruses,
– Not endospores
• Low-level disinfectants
– Removes fungi, vegetative bacteria
and enveloped viruses
– Not mycobacteria, naked viruses or
endospores
Chemicals as Control
• Selecting appropriate chemical
– Points to consider
• Toxicity
– Benefits must be weighed against risk of use
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Activity in presence of organic material
Compatibility with material being treated
Residue
Cost and availability
Storage and stability
Environmental risk
Chemicals as Control
• Classes of chemicals
– Germicides represent a number or chemical families
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Alcohols
Aldehydes
Biguanides
Ethylene oxide
Halogens
Metals
Ozone
Peroxides
Phenolics
Quaternary ammonium compounds
Chemicals as Control
• Alcohols
– Solutions of 60% - 80% isopropyl or ethyl alcohol kill
vegetative bacteria and fungi
• Not effective against endospores and some naked viruses
– Mechanism
• Coagulation of proteins and essential enzymes
• Damage to lipid membranes
– Commonly used as antiseptic and disinfectant
– Limitations
• Evaporates quickly limiting contact time
• May damage material such as rubber and some plastics
Chemicals as Control
• Aldehydes
– Mechanism:
– 2% glutaraldehyde solution most widely used
liquid sterilant
– Formalin used to kill bacteria and inactivate
viruses
• A solution made from formaldehyde
Chemicals as Control
• Hydrogen peroxide
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Powerful oxidizing agents
biodegradable
Less toxic
Effectiveness depends on surface being treated
• More effective on inanimate object
– Useful as disinfectant
• Leaves no residue
• Doesn’t damage most materials
– Hot solutions used in food industry
– Vapor-phase can be used as sterilant material
Chemicals as Control
• Chemical preservatives
– Weak organic acids often used as food preservatives
• Benzoic, ascorbic and propionic acids
• Mode of action
– Alter cell membrane function
– Interfere with energy transformation
– Nitrates and nitrites used in processed meats
• Inhibits germination of endospores and growth of vegetative
cells
• Have been shown to be potent carcinogen
Control of bacteria growth-chemical
• Reducing water availability
– Salting
– drying
Review
• Important concepts:
– Sterilization, pasteurization, D value etc.
• Methods to control bacteria growth
– Physical
– chemical
Review
• Considering factors when choose control
methods.
• Moister heat.
• Radiation (ionizing, nonionizing).
• The difference between different levels of
disinfectants.
Review
• Chemicals
– Ethanol
– Aldehyde
– Ethylene oxide
– Hydrogen Peroxides