Control of microbial growth week7
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Transcript of Control of microbial growth week7
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Masdiana Padaga
10/04/23
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Bacterial growth is increase in cell numbers
Growth depends on temperature, pH, osmotic pressure, oxygen, and nutrients
Log phase cultures are most sensitive to growth inhibition
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1. Physical
2. Chemical
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Sterilization vs. Disinfection Sterilization
destroying all forms of life Disinfection
destroying pathogens or unwanted organisms Disinfectant vs. Antiseptic Disinfectant
antimicrobial agent used on inanimate objects Antiseptic
antimicrobial agent used on living tissue
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Bactericidal - kills bacteria Bacteristatic - inhibits bacterial growth
Fungicidal Fungistatic Algacidal Algastatic
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Temperature Desiccation Osmotic pressure Radiation
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1. HeatMoist Heat
Boiling Water Steam Heat (Autoclave)
Dry Heat Direct Flaming Incineration Hot Air Sterilization (Oven)
2. Filtration 3. Radiation
Ionizing RadiationNon-Ionizing Radiation
4. Pasteurization (Heat)
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1. Heatworks by denaturing enzymes and proteins
A. Thermal Death Point (TDP) lowest temp. at which all microorganism in a
liquid culture are killed in 10 minutes B. Thermal Death Time (TDT)
minimum length of time in which all microorganisms in a liquid culture are killed at a given temperature
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• Sterilization is the killing of all organisms, including viruses. Heat is the most widely used method of sterilization. Often, however, we cannot attain sterility, but we can still control microorganisms effectively by limiting their growth, the process of inhibition.• Death from heating is an exponential function, occurring more rapidly as the temperature rises (Figure 20.1).
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•Figure 20.2 shows the relationship between temperature and the rate of killing as indicated by the decimal reduction time for two different microorganisms.
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1. Boiling Waterkills vegetative
bacterial cells, Fungi and many viruses
not effective for endospores and some viruses Hepatitis (20 min)
Some spores may survive boiling water for up to 20 hrs
2. Autoclave (Steam under pressure)preferred method of
sterilizationWater boils at 100 C Increasing the
pressure raises the Temp.
15 lbs./ per sq. inch (psi) ------> 121 C
121 C for 15 min.
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• An autoclave permits application of steam heat under pressure at temperatures above the boiling point of water, killing endospores (Figure 20.3).
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1. Direct Flaming Inoculating Loop and Needle 100%
effective 2. Incineration
disposable wastes (paper cups, bags, dressings)
3. Hot Air SterilizationOven ( 170 C for 2 hours)used on substances that would be
damaged by moist heat sterilization gauzes, dressings or powders
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Dry heat sterilizes.
a. Hot air ovens (160-170°C/2-3 hours) used when moisture is undesirable.
b. Incineration (burning) used to destroy disposable items,
soiled dressings, tissue specimens etc. @ 800°C to 6500°C
c. The hottest part of a Bunsen burner flame reaches 1,870°C for flaming during lab.
Microbiology is Fun!
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1. Ionizing Radiationgamma rays & x-rays
penetrates most substances penetrate solid or light-absorbing materials,
Used on substances that could be damaged by heat
is widely used for sterilization and decontamination in the medical and food industriesplastic petri dishes, plastic syringes, catheterssurgical gloves
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2. Non-Ionizing RadiationUV Light
does not penetrate plastic, glass or proteinaceous matter
Used to reduce microbial populationshospital rooms, nurseries, operating rooms used to decontaminate surfaces and
materials that do not absorb light, such as air and water.
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• Controlled doses of electromagnetic radiation effectively inhibit microbial growth. Table 20.1 shows the radiation sensitivity of microorganisms and biological functions.
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• The relationship between the survival fraction and the radiation dose is illustrated in Figure 20.5.
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does not sterilize liquids but reduces microbial load
killing most pathogens and inhibiting the growth of spoilage microorganisms.
Mycobacterium tuberculosis 63 C for 30 minutes 72 C for 15 seconds
(HTST)
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Removes microorganisms from solutions that might be damaged by heat
culture mediaenzymesvaccinesantibiotics
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• Membrane filters (Figure 20.7) are used for sterilization of heat-sensitive liquids, and nucleation filters are used to isolate specimens for electron microscopy.
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Refrigeration is bacteriostatic Most pathogens do not grow
Exception? Freezing: slow freezing creates ice crystals
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Desiccation : bacteriostatic lyophilization used to preserve cultures
Osmotic pressure – high concentrations of salt or sugar
Molds and yeasts most resistant
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• Chemicals that kill organisms are called cidal agents.
• these agents are termed •Bacteriocidal : killing bacteria,
• fungicidal,: killing fungi
•viricidal : killing viruses
Bacteriocidal agents bind tightly to their cellular targets and are not removed by dilution; but lysis, the loss of cell integrity and release of contents, does not occur.
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• Agents that do not kill but only inhibit growth are called static agents, and these include bacteriostatic, fungistatic, and viristatic agents.
Antimicrobial activity is measured by determining the smallest amount of agent needed to inhibit the growth of a test organism, a value called the minimum inhibitory concentration (MIC) (Figure 20.11).
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• Sterilants, disinfectants, and sanitizers are compounds used to decontaminate nonliving material. • Disinfection is the elimination of microorganisms from inanimate objects or surfaces. Table 20.3. Industrial uses of chemical antimicrobial•Antiseptics and germicides are used to reduce microbial growth on living tissues. •Table 20.4 lists some antiseptics, sterilants, disinfectants, and sanitizers.
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Factors effect Antimicrobial Activity
Targets of Antimicrobial Agents
1. Temp2. Time3. Concentration of
Antimicrobial agent4. Type of Microbe5. Activity of Microbe6. Presence of organic
matter
1. Cell membrane2. Enzymes &
Proteins3. DNA & RNA
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