Lesson18_Cultivation of microorganism

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Transcript Lesson18_Cultivation of microorganism

What are the physical and chemical methods that can be used
for controlling microbial growth and population?
 A treatment that kills or removes all living cells,
including viruses and spores, from a substance or
 A treatment that reduces the total number of microbes
on an object or surface, but does not necessarily
remove or kill all of the microbes
Reduction of the microbial population to levels
considered safe by public health standards.
 A mild disinfectant agent suitable for use on skin
 A suffix that mean “the agent kills.”
A bactericidal agent kills bacteria
 A suffix that means “the agent inhibits growth.”
A fungistatic agent inhibits the growth of fungi, but
doesn’t necessarily kill it.
Moist Heat
Dry Heat
Low Temperatures
A. Boiling at 100°C
 Effective against most vegetative cells;
 ineffective against spores
 unsuitable for heat sensitive chemicals & many
B. Autoclaving/pressure canning
 Temperatures above 100°C achieved by steam
 Sterilization in autoclave is used in biomedical or
clinical laboratory.
C. Pasteurization
 Used to reduce microbial numbers in milk and
other beverages while retaining flavor and food
quality of the beverage
 Traditional treatment of milk, 63°C for 30 min
 Flash pasteurization (high-temperature short
term pasteurization) - quick heating to about 72°C
for 15 sec, then rapid cooling
Oven sterilization
◦ Used for dry glassware & heat-resistant metal
◦ Typically 2 hr at 160°C is required to kill bacterial
spores by dry heat.
◦ around 4°C
◦ inhibits growth of mesophiles or thermophiles;
◦ “ordinary” freezer around -10 to -20°C
◦ Generally inhibits all growth; many bacteria and
other microbes may not survive freezing
Used for physically removing microbes and dust
particles from solutions and gasses.
Depth filters: e.g.. Diatomaceous earth, unglazed
Membrane filters: e.g.. Nitrocellulose,
HEPA filters: High efficiency particulate air filters
used in laminar flow in biological safety cabinets
Ultraviolet Radiation
◦ DNA absorbs ultraviolet radiation at 260 nm
◦ This causes damage to DNA
◦ Useful for continuous disinfection of work
surfaces, e.g. in biological safety cabinets
Ionizing Radiation
◦ Gamma radiation produced by Cobalt-60 source
◦ Powerful sterilizing agent;
◦ penetrates and damages both DNA and protein;
effective against both vegetative cells and spores
◦ Often used for sterilizing disposable plastic lab
◦ Also can be used for sterilization of food;
◦ has been approved but has not been widely
adopted by the food industry
Heavy metals
Quaternary Ammonium Compounds
Sterilizing Gases
Evaluating Effectiveness of Chemical Agents
Aromatic organic compounds with attached -OH
Denature protein & disrupt membranes
Phenols: Commonly used as disinfectants (e.g.
are tuberculocidal, effective in presence of organic
matter, remain on surfaces long after application
Ethanol; isopropanol; used at concentrations
between 70 – 95%
Denature proteins; disrupt membranes
Kills vegetative cells of bacteria & fungi but not
Used in disinfecting surfaces; thermometers;
“ethanol-flaming” technique used to sterilize glass
plate spreaders or dissecting instruments at the lab
Act as oxidizing agents - oxidize proteins & other
cellular components
Chlorine compounds
◦ Used in disinfecting municipal water supplies (as
sodium hypochlorite, calcium hypochlorite, or
chlorine gas)
◦ Sodium Hypochlorite (Chlorine Bleach) used at 10
- 20% dilution as common disinfectant
Iodine Compounds
◦ Tincture of iodine (iodine solution in alcohol)
◦ Potassium iodide in aqueous solution
◦ Iodophors: Iodine complexed to an organic carrier;
e.g. Wescodyne, Betadyne
◦ Used as antiseptics for cleansing skin surfaces and
Mercury, silver, zinc, arsenic, copper ions
Form precipitates with cell proteins
At one time were frequently used medically as
antiseptics but much of their use has been replaced by
less toxic alternatives
Quaternary ammonium compounds are cationic
Amphipathic molecules that act as emulsifying
Denature proteins and disrupt membranes
Used as disinfectants and skin antiseptics
Examples: cetylpyridinium chloride, benzalkonium
Formaldehyde and gluteraldehyde.
React chemically with nucleic acid and protein,
inactivating them
Aqueous solutions can be used as disinfectants
Ethylene oxide (EtO)
◦ Used to sterilize heat-sensitive equipment and
plastic ware
◦ Much of the commercial use of EtO (for example,
plastic petri dishes) has in recent years been
replaced by gamma irradiation
Betapropiolactone (BPL)
◦ In its liquid form has been used to sterilize
Vapor-phase hydrogen peroxide
◦ Has been used recently to decontaminate biological
safety cabinets