1. Control of Microorganisms Microbiology 2011

2. Group Discussions
What are the physical and chemical methods that can be used for controlling microbial growth and population?

3. Sterilization:
A treatment that kills or removes all living cells, including viruses and spores, from a substance or object
Disinfection:
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

4. Sanitation:
Reduction of the microbial population to levels considered safe by public health standards.
Antiseptic:
A mild disinfectant agent suitable for use on skin surfaces.
-cidal:
A suffix that mean “the agent kills.”
A bactericidal agent kills bacteria

5. -static:
A suffix that means “the agent inhibits growth.”
A fungistatic agent inhibits the growth of fungi, but doesn’t necessarily kill it.

6. Physical Methods Moist Heat Dry Heat Low Temperatures Filtration
Radiation

7. 1. Moist Heat
A. Boiling at 100°C
Effective against most vegetative cells;
ineffective against spores
unsuitable for heat sensitive chemicals & many foods.
B. Autoclaving/pressure canning
Temperatures above 100°C achieved by steam pressure
Sterilization in autoclave is used in biomedical or clinical laboratory.

8. Traditional treatment of milk, 63°C for 30 min
Moist Heat……..
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

9. 2. Dry Heat Oven sterilization
Used for dry glassware & heat-resistant metal equipment
Typically 2 hr at 160°C is required to kill bacterial spores by dry heat.

10. 3. Low Temperatures Refrigerator: around 4°C
inhibits growth of mesophiles or thermophiles; psychrophiles.
Freezer:
“ordinary” freezer around -10 to -20°C
Generally inhibits all growth; many bacteria and other microbes may not survive freezing temperatures

11. 4. Filtration
Used for physically removing microbes and dust particles from solutions and gasses.
Depth filters: e.g.. Diatomaceous earth, unglazed porcelain
Membrane filters: e.g.. Nitrocellulose,
HEPA filters: High efficiency particulate air filters used in laminar flow in biological safety cabinets

12. 5. Radiation Ultraviolet Radiation
DNA absorbs ultraviolet radiation at 260 nm wavelength
This causes damage to DNA
Useful for continuous disinfection of work surfaces, e.g. in biological safety cabinets

13. Gamma radiation produced by Cobalt-60 source
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 ware.
Also can be used for sterilization of food;
has been approved but has not been widely adopted by the food industry

14. Chemical Agents Phenolics Alcohols Halogens Heavy metals
Quaternary Ammonium Compounds
Aldehydes
Sterilizing Gases
Evaluating Effectiveness of Chemical Agents

15. 1. Phenolics Aromatic organic compounds with attached -OH
Denature protein & disrupt membranes
Phenols: Commonly used as disinfectants (e.g. “Lysol”);
are tuberculocidal, effective in presence of organic matter, remain on surfaces long after application

16. 2. Alcohols
Ethanol; isopropanol; used at concentrations between 70 – 95%
Denature proteins; disrupt membranes
Kills vegetative cells of bacteria & fungi but not spores
Used in disinfecting surfaces; thermometers; “ethanol-flaming” technique used to sterilize glass plate spreaders or dissecting instruments at the lab bench

17. 3. Halogens
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 % dilution as common disinfectant

18. Tincture of iodine (iodine solution in alcohol)
Halogens……………..
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 wounds

19. 5. Heavy Metals 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

20. 6. Ammonium Compounds
Quaternary ammonium compounds are cationic detergents
Amphipathic molecules that act as emulsifying agents
Denature proteins and disrupt membranes
Used as disinfectants and skin antiseptics
Examples: cetylpyridinium chloride, benzalkonium chloride

21. 7. Aldehydes Formaldehyde and gluteraldehyde.
React chemically with nucleic acid and protein, inactivating them
Aqueous solutions can be used as disinfectants

22. 8. Sterilizing Gases 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

23. 9. Sterilizing Gases Betapropiolactone (BPL)
In its liquid form has been used to sterilize vaccines.
Vapor-phase hydrogen peroxide
Has been used recently to decontaminate biological safety cabinets

24. END