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7th Lab
CHEMICAL AND PHYSICAL EFFECTS ON
BACTERIAL GROWTH
• 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
Factors that influence effectiveness
Number of microbes
Conc.and kind of agents used
Time exposure
Microbial characteristics
METHODS OF CONTROL
ChemicalAntimicrobial agents
Chemical depends on circumstances and degree of control
require
PhysicalHeat (Temperature)
Radiation
Filtration
PHYSICAL CONTROLS:
HEAT
Dry Heat Sterilization kills by oxidation
Dry Heat Sterilization Kills by oxidation
Flaming
Incineration
Hot-air sterilization
Dry Heat
• Moist heat
denatures
proteins
• Autoclave:
Steam under
pressure
• 15 min at 121oC
at 15 psi
AUTOCLAVING PHYSICAL CONTROLS
Escherichia colisubtilisBacillusTemperature
60 mins30 mins60 mins30 mins
5C
RT
37 C
55 C
70 C
90C
PASTEURIZATIONPHYSICAL CONTROLS
63oC for 30 minutes
72oC for 15 seconds
140oC for 1 second
Pasteurization reduces spoilage organisms and pathogens
http://www.mun.ca/biology/scarr/Thymine-
Thymine_Dimers.html
Radiation UV Physical Controls
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)
Time
1 second
5 second
10 second
30 second
45 second
50 second
60 second
Led on
• Micrococcus luteus
RADIATION
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
15% NaCl10%NaCl5%NaCl
Salt
concentration
Figure : The growth of Escherichia coli and Staphylococcus aureus in Nacl concentrations of 5%,10%,15% respectively
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