Microbial Control Methods and Their Applications

Decontamination

The process of removing or reducing harmful microorganisms to a safe level.

Sterilization

The complete elimination of all forms of microbial life, including spores.

Disinfection

The process of killing or inhibiting harmful microorganisms, but not necessarily all microbes, especially spores.

When is sterilization used?

Sterilization is used when it's essential to completely eliminate all microbes, especially in medical settings, for surgical instruments, or for laboratory equipment.

When is disinfection used?

Disinfection is used when it's necessary to reduce microbial load on surfaces or inanimate objects, but complete sterility is not required, such as cleaning surfaces in hospitals or kitchens.

At what refrigeration temperature can we slow the growth of microbes?

Microbial growth is slowed at temperatures between 0°C and 4°C.

At what freezer temperature can we slow the growth of microbes?

In freezers, temperatures of -18°C or lower can slow down microbial growth.

What is refrigeration used for?

Refrigeration is used to slow the growth of microorganisms in food and other perishable items to extend their shelf life.

Thermal death time

The time required to kill a specific microorganism at a given temperature.

Thermal death point

The lowest temperature at which a microorganism is killed in a specified time.

Examples of heat-related control methods

Examples include autoclaving, boiling, dry heat sterilization, and pasteurization.

What is an autoclave and what is it used for?

An autoclave is a high-pressure steam sterilizer used to sterilize medical equipment, laboratory tools, and other items that require complete microbial elimination.

What are the standard autoclave settings for time, pressure, and temperature?

Time: 15-20 minutes; Pressure: 15 psi (pounds per square inch); Temperature: 121°C (250°F).

What are the disadvantages of using an autoclave?

Autoclaves may damage heat-sensitive materials, and not all items can tolerate high pressure and temperature.

What organisms are destroyed by boiling water for 5 minutes?

Destroyed: Most vegetative bacteria and viruses. Not destroyed: Bacterial spores, like those of Clostridium botulinum.

Is boiling a decontamination, sterilization, or disinfection strategy?

Boiling is a disinfection method as it kills many microorganisms but does not sterilize.

What is pasteurization and what is it used for?

Pasteurization is a heat treatment method used to kill pathogens in food and beverages, especially liquids like milk and juice, without affecting taste or quality.

What pathogens found in milk are affected by pasteurization?

Pathogens like Salmonella, Listeria, and E. coli are killed by pasteurization.

Why is milk refrigerated after pasteurization?

Refrigeration slows microbial growth and preserves the milk's quality after pasteurization.

What is dry heat?

Dry heat involves sterilization using high temperatures without moisture, such as in an oven or hot air sterilizer.

List examples of dry heat sterilization.

Examples include hot air ovens and incineration.

High-pressure processing

A method used to kill harmful bacteria in food products while preserving the food's texture and nutrients.

Desiccation

The drying out of microorganisms, which can be accelerated by using dehydrators or applying heat.

Lyophilization

A method of preserving microorganisms or biological materials by freezing them and then removing the water through sublimation.

Radiation

The use of electromagnetic energy, like UV light or gamma rays, to kill or inactivate microorganisms.

Ionizing radiation

Gamma rays and X-rays, which destroy microbes by breaking DNA strands.

Non-ionizing radiation

UV light, which damages microbial DNA.

HEPA filter

High-efficiency particulate air filters used in hospitals, laboratories, and air purifiers to remove particles like dust, bacteria, and allergens from the air, but they don't remove gases or odors.

LifeStraws

Portable water filters that remove bacteria, protozoa, and other contaminants but do not sterilize water, as they don't eliminate viruses or some pathogens.

Intermediate-level disinfectant alcohols

Ethanol and isopropanol, which denature proteins, disrupting microbial cell membranes, and are used for disinfecting surfaces and medical equipment.

Disadvantages of using alcohol

Alcohols can evaporate quickly and may not be effective against all pathogens, like spores.

Aldehydes in healthcare

Formaldehyde and glutaraldehyde are used to kill bacteria and viruses by crosslinking proteins and nucleic acids, and they are used for sterilizing medical equipment.

Disadvantages of aldehydes

Aldehydes can be toxic and irritating, requiring careful handling and ventilation.

Newest aldehyde

Orthophthalaldehyde (OPA), which is less toxic than glutaraldehyde and is used for high-level disinfection.

Phenols

Used as disinfectants in cleaning products and some antiseptic formulations.

Triclosan

A phenol found in antibacterial soaps, plastics, and textiles.

How phenols work

Phenols denature proteins and disrupt cell membranes, used for surface disinfection, but can be toxic and irritating to skin.

Examples of halogens

Chlorine, iodine, and bromine.

How halogens work

Halogens work by oxidizing and denaturing microbial proteins and can be inactivated by organic material or reduced pH.

Most widely used halogen disinfectant

Chlorine, used for disinfecting drinking water and swimming pools.

Iodine

Iodine is used as a disinfectant and antiseptic, effective against bacteria, viruses, and fungi.

Heavy Metals

Examples include silver, copper, and mercury.

Uses of Heavy Metals

Heavy metals are used for antimicrobial purposes, such as in wound dressings or water purification.

Disadvantages of Heavy Metals

Heavy metals can be toxic and accumulate in the body, leading to poisoning.

Common Peroxygens

Common peroxygens include hydrogen peroxide and peracetic acid, which attack cell membranes, proteins, and DNA.

High-Level Disinfectants

Peroxygens are considered high-level disinfectants at high concentrations.

Hydrogen Peroxide Uses

Hydrogen peroxide can disinfect surfaces, wounds, and medical equipment.

Peracetic Acid Effectiveness

Peracetic acid is effective in the presence of organic material.

Dialysis Centers Disinfectants

Dialysis centers use newer disinfectants with peracetic acid and hydrogen peroxide together for hemodialyzers.

Ethylene Oxide State

Ethylene oxide is a gas.

Ethylene Oxide Sterilization

Ethylene oxide is a good sterilization method. It damages microbial DNA and proteins.

Ethylene Oxide Applications

Ethylene oxide can be used on medical equipment and sensitive materials.

Disadvantages of Ethylene Oxide

Ethylene oxide is toxic, flammable, and requires special handling.

Detergents

Detergents are cleaning agents that damage microbial cell membranes.

Classes of Detergents

The classes include anionic, cationic, and non-ionic detergents.

Bisbiguanides Effect

Bisbiguanides disrupt the microbial cell membrane.

Examples of Bisbiguanides

Examples: Chlorhexidine and alexidine. They are used for skin antisepsis.

Pressurized Carbon Dioxide Characteristics

Pressurized carbon dioxide is used in supercritical fluid form for sterilization and preservation.

Pressurized Carbon Dioxide Uses

Pressurized carbon dioxide can be used to sterilize medical devices, implants, and transplanted tissues.

Chemical Preservatives

Acetic acid and lactic acid are added to food. They target microbial growth by lowering pH.

Naturally Produced Preservatives

Nisin and natamycin are naturally produced preservatives.

Nisin and Natamycin Uses

Nisin is used against Gram-positive bacteria, and natamycin is used against fungi.

Factors for Selecting Germicides

Factors include type of microorganism, material compatibility, toxicity, and contact time.