Download Controlling Microorganisms

Topic 14 (Ch 11/9)
Physical and Chemical Control
of Microbes
Topics
- Controlling Microorganisms
- Physical Control
- Chemical control
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Microbial Control Methods Overview
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Controlling Microorganisms
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Microbial agents
Sanitation
Effectiveness
Mode of action
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Microbial agents
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-static agents
-cital agents
Resistance
Terms
Effectiveness
Mode of action
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-static agents
• Temporarily preventing the growth of
microbes
– Bacteriostatic
– Fungistatic
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-cital
• Killing or destroying a microorganism
– Germicide
– Bactericide
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Terminology
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Relative Resistance
• Highest resistance - bacterial spores and
prions
• Moderate resistance - some bacteria,
protozoan cysts, fungal sexual spores, naked
viruses
• Least resistance - most bacteria, fungal
nonsexual spores and hyphae, enveloped
viruses, yeast, protozoan trophozoites
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Relative Resistance
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Terms
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Sterilization
Disinfection
Antisepsis
Sanitation
Degermination
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Sterilization
• A process that destroys or removes all
viable microorganisms, including spores
and viruses
• Physical or chemical agents
• Inanimate objects
– Surgical instruments, commercially
packaged foods
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Disinfection
• Use of physical process or chemical
agent (disinfectant) to destroy
vegetative pathogens.
• Removes toxins
• Not bacterial endospores
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Antisepsis
• Chemical agents (antiseptics) destroy or
inhibit vegetative pathogens
• Skin and mucous membranes
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Sanitation
• Reducing the number of
microorganisms
• Physical chemical agents
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Degermination
• Human skin - reducing the number of
microorganisms
• Physical and chemical agents
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Effectiveness
• Number of microorganisms
• Target population (bacteria, fungi,
spores, viruses)
• Temperature and pH
• Concentration of agent
• Mode of action
• Interfering agents (solvents, debris,
saliva, blood, feces)
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Factors that influence effectiveness of antimicrobial agents
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Susceptibility
• Germicides  classified as high,
intermediate, or low effectiveness
– High-level = kill all pathogens, including
endospores
– Intermediate-level = kill fungal spores,
protozoan cysts, viruses, pathogenic
bacteria
– Low-level kill = vegetative bacteria, fungi,
protozoa, some viruses
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How to Select?
– Inexpensive
– Fast-acting
– Stable during storage
– Capable of controlling microbial growth
while being harmless to humans, animals,
and objects
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Antimicrobial Agents
– Alteration of cell walls and membranes
• Cell wall maintains integrity of cell
– Cells burst due to osmotic effects when damaged
• Cytoplasmic membrane contains cytoplasm
and controls passage of chemicals into and out
of cell
– Cellular contents leak out when damaged
• Nonenveloped viruses have greater tolerance
of harsh conditions
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Actions of Antimicrobials
– Damage to proteins and nucleic acids
• Protein function depends on 3-D shape
– Extreme heat or certain chemicals denature proteins
• Chemicals, radiation, and heat can alter or
destroy nucleic acids
– Can produce fatal mutants
– Can halt protein synthesis through action on RNA
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Mode of action
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Cell wall
Cell membrane
Nucleic acid synthesis
Protein synthesis
Protein function
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Cell wall
• Bacteria and fungi
– Block synthesis
– Degrade cellular components
– Destroy or reduce stability
• Agent
– Penicillin, detergents, alcohols
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Cell membrane
• All microbes and enveloped viruses
– Bind and penetrate lipids
– Lose selective permeability (leakage)
• Agent
– Surfactants
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Surfactant effect on cell membranes
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Nucleic acid synthesis
• Irreversible bind to DNA
– Stop transcription and translation
– mutations
• Agent
– Chemical agent – formaldehyde
– Physical agent – radiation
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Protein synthesis
• Binds to ribosomes
– Stops translation
– Prevents peptide bonds
• Agent
– chloramphenicol
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Protein function
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Block protein active sites
Prevent binding to substrate
Denature protein
Agent
– Physical – Heat, pH change
– Chemical – alcohols, acids, phenolics,
metallic ions
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Effects of heat, pH, and blocking agents on protein function
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Physical Control
• Heat
• Radiation
• Filtration
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Heat
• Mode of action
• Moist
• Dry
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Mode of action
• Moist heat
– Coagulation of proteins
– Denaturation of proteins
• Dry heat
– Dehydration
– Denaturation
– Oxidation (burning to ashes)
• Thermal death time
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Moist heat
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Steam and pressure
Tyndallization
Pasteurization
Boiling water
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Steam and pressure
• Pressure above normal atmospheric
pressure will result in temperatures
above 100˚C
• Effectively destroys spores
• Sterilizes inanimate objects (glassware)
• Ex. Autoclave and home pressure
cooker
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Diagram of an autoclave
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Tyndallization
• Intermittent sterilization
• Used for heat-sensitive media, canned
foods
• Will not destroy spores
• Ex. Exposure to free-flowing steam for
30 to 60 minutes
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Pasteurization
• Disinfection of beverages
• Exposes beverages to 71.6 ˚C for 15 seconds
– Stops fermentation
• Prevents the transmission of milk-borne
diseases
– Salmonella, Campylobacter, Listeria,
Mycobacteria
• Examples: Milk industry, wineries, breweries
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Boiling water
• Decontaminates at 100 ˚C for 30
minutes
• Kills most non-spore forming pathogens
• Examples: home sanitizing and
disinfecting, disinfecting unsafe water
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Dry heat
• Hot air
• Incineration
• Temperature and time of exposure is
greater than moist heat
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Hot air
• Hot air
– Oven
– Effective at 150˚C to 180˚C for 2-4 hrs
– Effective for inanimate objects and oils
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Incineration
• Destroys microbes to ashes or gas
– Flame - 1870˚C
– Furnace - 800˚C to 6500˚C
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Cold and Desiccation
• Cold temperatures reduce the activity of
some microbes, not psychrophiles
– Not a disinfection or sterilization method
• Desiccation or dehydration kill some
microorganisms
– Lyophilization – freezing and drying
method used to preserve microbes
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Radiation
• Types of radiation
• Modes of action
• Applications
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Types of radiation
• Ionizing
– Gamma rays (High energy)
– X-rays (Intermediate energy)
– Cathode rays (least energy)
• Nonionizing
– Ultraviolet
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Mode of actions
• Ionizing radiation ejects orbital electrons
from an atom
– High energy
• Penetrates liquids and solids effectively
• Nonionizing radiation raises atoms to a
higher energy state
– Low energy
• Less penetration capability
• Pyrimidine dimers
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Effects of ionizing and
nonionizing radiation on
DNA
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Ultraviolet (UV)
radiation
Ultraviolet (UV) radiation
can cause the formation of
pyrimidine dimers on DNA
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Radiation applications
• Ionizing radiation
– Alternative sterilization method
– Materials sensitive to heat or chemicals
– Some foods (fruits, vegetables, meats)
• Nonionizing radiation
– Alternative disinfectant
– Germicidal lamp in hospitals, schools, food
preparation areas (inanimate objects, air, water)
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A UV treatment system to disinfect water
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Filtration
• Removes microbes and spores from
liquids and air
• Perforated membrane
– Pore sizes vary
• Applications
– Liquids that are sensitive to heat
• Serum, vaccines, media
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Membrane filtration system
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Chemical control
• Widely used agents
• Applications
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Chemical agents,
target microbes, level of activity, and toxicity
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Chemical applications
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Halogens
Phenolics
Surfactants
Hydrogen peroxide
Detergents and soaps
Heavy metals
Aldehydes
Gases
Dyes, acids, and alkalis
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Halogens
• Chlorine
– Disinfectant and antiseptic
• Disrupt sulfhydryl groups in amino acids
• Iodine
– Topical antiseptic
• Disruption is similar to chlorines
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Phenolics
• Vary based on functional groups
attached to the aromatic ring
• Examples: Hexachlorophene,
Triclorsan
– Microcidal
– Ingredient in soaps to kitty litter
• Disrupts cell walls and membranes,
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Phenolics
(basic phenolic aromatic ring with various functional groups)
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Alcohols: R-OH
• Ethyl alcohol, isopropyl (rubber alcohol)
– 70% concentration dissolve membrane lipids,
disrupt cell surface tension, denatures proteins
• Germicidal and skin degerming
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Hydrogen peroxide
• Colorless and caustic liquid
• Form hydroxyl free radicals
– Effective against anaerobes
• Skin and wound cleaner
• Quick method for sterilizing
medical equipment
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Detergents and soaps
• Quaternary ammonium (quats)
– Cationic
– Bind and disrupt cell membrane
– Low-level disinfectant in the clinical setting
• Soaps
– Fatty acids, oils, sodium or potassium salts
– Cleaning agents
– More effective if mixed with germicides
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Detergents: + charge region binds bacteria, uncharged
region integrates into cell membrane
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Handscrubbing
Comparison:
non-germicidal vs. germicidal soap
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Heavy metals
• Mercury, silver,
– Inactivate proteins
– Preservatives in cosmetics and ophthalmic
solutions
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Effect of Ag and AU on microbial growth
heavy metal oligodynamic action
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Aldehydes
• Glutaraldehyde
– Crosslink with
proteins on the cell
surface
– Disinfectant for
surgical instruments
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Action of Glutaraldehyde
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Gases
• Ethylene oxide
– Reacts with
functional groups of
DNA and proteins
– Sterilizes and
disinfects plastic
materials
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Dyes
• Crystal violet
• Effective against Gram positive bacteria
• Ointments
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Acids and alkalis
• Acetic acid
• Ammonium
hydroxide
• Prevents spore
germination and
vegetative growth
• Food preservative
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