second part controlling microbial growth in the environment
TRANSCRIPT
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Second partCONTROLLING MICROBIAL
GROWTH IN THE ENVIRONMENT
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Topic Outline
1. Basic Principles of Microbial Control
2. The Selections of Microbial Control Methods
3. Physical Methods of Microbial Control
4. Chemical Methods of Microbial Control
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Basic Principles of Microbial Control1. Terminology of Microbial Control
• Sterilization – The removal or destruction of all microbes, including viruses and bacterial endospores, in or on an object.
• Aseptic – An environment or procedure that is free of contamination by pathogens.
• Disinfection – The use of physical or chemical agents known as disinfectants.
• Degerming – The removal of microbes from a surface by scrubbing.
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• Sanitization – The process of disinfecting places and utensils used by the public to reduce the number of pathogenic microbes to meet accepted public health standards.
• Pasteurization – The use of heat to kill pathogens and reduce the number of spoilage micoorganisms in food and beverages.
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2. Microbial Death Rates
• Definition – The permanent loss of reproductive ability under ideal environmental conditions.
• Technique for evaluating the efficacy of an antimicrobial agent.
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3. Action of Antimicrobial Agents• Modes of action fall into two basic catagories.
i. Alteration of cell walls (fungi) and membranes (virus).
- Give damage to a membrane’s proteins or phospholipids and therefore allows the cellular contents to leak out and causes death.
- Give damage to viral envelope that interrupts the reproduction.
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ii. Damage to proteins and nucleic acids.
- By breaking hydrogen and disulfide bonds in three dimensional shape and resulting in proteins denaturation. Proteins cease to function.
- Genes of a cell or virus are composed of nucleid acids. Disruption of nucleic acid can produce fatal mutation.
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The Selection of Microbial Control Methods1. Factors Affecting the Efficacy of Antimicrobial Methods
i. Site to be treated
- Harsh chemicals and extreme heat cannot be used on human, animals and fragile objects.
- To sterilized the utensils to be used on the body to prevent infections.
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ii. Relative susceptibility of microorganisms- Often to select a method to kill the hardiest
microorganisms present, assuming that method will kill more fragile microbes as well.
- Germicides can be classified as high, intermediate or low depending on their effectiveness on inactivating or destroying microorganisms.
- a. High-level kill all pathogens, including endospores.
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b. Intermediate-level kill fungal spores, protozoan cysts, viruses and pathogenic bacteria.
c. Low-level kill vegetative bacteria, fungi, protozoa and some viruses.
iii. Environmental conditions- Temperature: warm disinfectants work
better than cool ones. - pH: some disinfectants more effective at
low pH.- To clean objects before sterilization.
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2. Methods for Evaluating Disinfectants and Antiseptics
i. Phenol coefficient- The first method used.- If >1.0 ; the agent is more effective than
phenol.- The larger the ratio, the greater the
effectiveness.ii. Use-Dilution Test- The current standard test- The most effective agent is the one that
entirely prevents microbial growth at the highest dilution.
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iii. In-use test
- A more realistic method.
- Swabs are taken from actual objects before and after application of disinfectant.
- More accurate determination of a given disinfection agent for each specific situation.
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PHYSICAL METHODS OF MIROBIAL CONTROL
1. Heat Related Methods- High temperatures denature proteins, interfere
with the integrity of cytoplasmic membranes and cell walls and disrupt the function and structure of nucleic acids.
- Thermal death point: lowest temperature that that kills all cells in a broth in 10 minutes.
- Thermal death time: the time it takes to completely sterilize a particular volume of liquid at a set temperature.
- Decimal reduction time (D): time required to destroy 90% of the microbes in a sample.
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i. Moist heat- To disinfect, sanitize, sterilize and pasteurize
by denaturing proteins and destroying cytoplasmic membranes.
- More effective than dry heat because water is better conductor of heat than air.
- Methods: Boiling, Autoclaving, Pasteurization and Ultrahigh-Temperature Sterilization.
ii. Dry heat- Denatures proteins and fosters the oxidation of
metabolic and structural chemicals.- For substances cannot be sterilized by boiling
or steam or materials can be damaged by repeated exposure to steam.
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• endospores are very heat resistance.They are to survive heat that would rapidly kill vegetative cells of the same species.
• a major factor in heat resistance is the amount and state of water within the endospores.
• during endospores formation, the protoplasma is reduced to a minimum volume as a result of the accumulation of Ca2+-dipicolinic acid complexes.
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• also the protection of spore DNA by small acid-soluble proteins (SASP).
• this mixture forms a gel in the cytoplasm.• a thick cortex then forms around the
protoplast core.• contraction of the cortex results in a
shrunken, dehydrated protoplast with a water content of only 10-30% of a vegetative cells.
• high concentration of SASPs and low water content will give high heat resistance.
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- A routine part of standard aseptic in microbiology laboratory procedure .
- Requires higher temperatures for longer times than moist heat.
2. Refrigeration and Freezing- Tempt. is between 0oC and 7oC for
refrigeration and below 0oC for freezing.- Will decrease microbial metabolism,
growth and reproduction.- Because slow in chemical reactions and
unavailable of liquid.
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3. Desiccation And Lyophilization- Dessication or drying inhibits microbial
growth because the absent of water.- Lyophilization- technique combining
freezing and drying to preserve microbes and cells.
4. Filtration- The passage of a fluid (liquid or gas)
through a sieve to trap and separate particles (cells or viruses) from the fluid.
- To sterilize heat-sensitive materials (antibiotics, vaccines, enzymes etc.).
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5. Osmotic Pressure- Cells in hypertonic solution (concentrated
salt or sugar) will lose water and therefore inhibits cellular metabolism.
6. Radiation.- Particulate radiation : consists high-
speed subatomic particles that have been freed from their atoms.
- Electromagnetic radiation: energy without mass traveling in waves in the speed of lights.
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i. Ionizing Radiation
- Wavelengths shorter than 1 nm.
- Electron beams, gamma rays, and X rays.
ii. Nonionizing Radiation
- Wavelength greater than 1 nm.
- UV light, visible light, infrared radiation and radio waves.
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CHEMICAL METHODS OF MICROBIAL CONTROL
i. Phenol and phenolics.- Phenolics: compounds derived from phenol
molecules that have been chemically modified by the addition of halogens or organic functional groups.
- Commonly used in health care settings, laboratories and households.
- -ve: disagreeable odor and possible side effect (skin irritation, brain damage in infants).
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ii. Alcohols
- intermediate-level disinfectants.
- Commonly used are isopropanol and ethanol.
- Denature proteins and disrupt cytoplasmic membranes.
- Pure alcohol is not an effective as 70% and 90% because no water.
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• in microbial control, alcohols acts on proteins and disrupt cytoplasmic membranes.
• however, water is needed for the coagulation reactions of proteins.
• this also called denaturation of proteins. • 100% ethanol contained no water to carry on the
coagulation process and therefore not effective in microbial control.
• moreover, 70% alcohol-water mixture penetrates more deeply than pure alcohol into most materials to be disinfected.
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iii. Halogens (I-, Cl-, Br-, Fr-)
- Used both alone and combined with other elements in organic and inorganic compounds
- Iodine: well-known antiseptic for water.
- Iodophor (iodine-containing organic compound): used in medical institution.
- Chlorine: treat drinking water, swimming pools and waste water.
- Sodium/calcium hypochlorite: disinfectant.
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iv. Oxidizing Agents- peroxides, ozone and peracetic acid.- High-level disinfectants and antiseptics.- Used by health care workers to kill anaerobes in
deep puncture wounds.
v. Surfactants- To reduce the surface tension of solvents
(water) by decreasing the attraction among molecules that the solvent becomes more effective at dissolving solute molecules (exp. Oils) and any bateria they harbor – are more easily wash away.
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vi. Heavy metals- Such as arsenic, zinc, mercury, silver and
copper.- Can combine with sulfur atoms in molecules of
cystein, an amino acid.- Low-level bacteriostatic and fungistatic agents.
vii. Aldehydes- Compounds containing terminal –CHO groups.- Usually used by hospital personnel for
disinfecting medical and dental equipments.- Formadehyde irritates mucous membranes and
is carcinogenic.
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viii. Gaseous Agents
- Suitable for large or bulky items.
- Sterilized within a closed chamber containing highly reactive microbicidal and sporicidal gases such as ethylene oxide, propylene oxide, and beta-propiolactone.
- Can be extremely hazardous to the people using them.
ix. Antimicrobials Drugs
- antibiotics, semisynthetics and synthetics.
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- Antibiotics: chemicals produced naturally by microorganisms.
i. from fungi
ii from bacteria
- Semisynthetic: antibiotic undergo modification.
- Typically used for treatment of disease.