8th lab physical effect on microbial growth tue
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Transcript of 8th lab physical effect on microbial growth tue
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7th Lab
CHEMICAL AND PHYSICAL EFFECTS ON
BACTERIAL GROWTH
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• Phenol
• Halogens (Chlorine, iodine, bromine)
• Alcohols (e.g.. isopropyl alcohol)
• Heavy metals (Ag, Hg, Cu, Zn)
• Surface active agents (soaps & detergents)
• Quaternary Ammonium Cmpds(quats)
• Aldehydes (e.g.. glutaraldehyde)
• Heat: Moist vs. Dry
• Autoclaving, pasteurization
• Filtration
• Cold
• Desiccation & high osmotic
pressure
• Radiation (UV, gamma rays)
WHAT FACTORS LIMIT MICROBIAL GROWTH
Physical Control Methods Chemical Control Methods
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Factors that influence effectiveness
Number of microbes
Conc.and kind of agents used
Time exposure
Microbial characteristics
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METHODS OF CONTROL
ChemicalAntimicrobial agents
Chemical depends on circumstances and degree of control
require
PhysicalHeat (Temperature)
Radiation
Filtration
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PHYSICAL CONTROLS:
HEAT
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Dry Heat Sterilization kills by oxidation
Dry Heat Sterilization Kills by oxidation
Flaming
Incineration
Hot-air sterilization
Dry Heat
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• Moist heat
denatures
proteins
• Autoclave:
Steam under
pressure
• 15 min at 121oC
at 15 psi
AUTOCLAVING PHYSICAL CONTROLS
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Escherichia colisubtilisBacillusTemperature
60 mins30 mins60 mins30 mins
5C
RT
37 C
55 C
70 C
90C
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PASTEURIZATIONPHYSICAL CONTROLS
63oC for 30 minutes
72oC for 15 seconds
140oC for 1 second
Pasteurization reduces spoilage organisms and pathogens
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http://www.mun.ca/biology/scarr/Thymine-
Thymine_Dimers.html
Radiation UV Physical Controls
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RadiationPhysical Controls
Ionizing radiation (X rays, gamma rays, electron
beams)
• Ionizing water and other molecules to form
radicals that disrupts proteins and DNA
• surgical supplies, plastic syringes
Nonionizing radiation UV
DNA damage (260 nm Thymine dimers)
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Time
1 second
5 second
10 second
30 second
45 second
50 second
60 second
Led on
• Micrococcus luteus
RADIATION
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DesiccationVery variable effect on microbes, many can survive extended times (months), some endospore for centuries, others die in minutesUsed usually for hospital & nursing home microbiology, Osmotic PressureHigh salt or sugar content (hypertonic conditions)
Other Physical Controls
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15% NaCl10%NaCl5%NaCl
Salt
concentration
Figure : The growth of Escherichia coli and Staphylococcus aureus in Nacl concentrations of 5%,10%,15% respectively
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Filtration
For heat sensitive solutions/liquids
Cellulose esters or plastic polymers (pore
size from 0.01-0.45 µm)
Used for :
Culture media
Laboratory reagents
Pharmaceutical products
Culture mediaLaboratory reagentsPharmaceutical
products