Microbial Control Methods and Germicides

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?

When it's essential to completely eliminate all microbes, such as in medical settings or laboratory equipment.

When is disinfection used?

When it's necessary to reduce microbial load on surfaces or inanimate objects, but complete sterility is not required.

Refrigeration temperature for slowing microbial growth

Between 0°C and 4°C.

Freezer temperature for slowing microbial growth

At temperatures of -18°C or lower.

Refrigeration purpose

To slow the growth of microorganisms in food and other perishable items.

Thermal death time

Time required to kill a microorganism at a given temperature.

Thermal death point

Lowest temperature at which a microorganism is killed in a specified time.

Heat-related control methods

Autoclaving, boiling, dry heat sterilization, and pasteurization.

Autoclave

An autoclave is a high-pressure steam sterilizer used to sterilize medical equipment and laboratory tools.

Standard autoclave settings

Time: 15-20 minutes, Pressure: 15 psi, Temperature: 121°C (250°F).

Disadvantages of using an autoclave

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

Boiling water for 5 minutes

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

Boiling method classification

Boiling is a disinfection method.

Pasteurization

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.

Pathogens affected by pasteurization in milk

Salmonella, Listeria, and E. coli.

Refrigeration of milk after pasteurization

To slow microbial growth and preserve the milk's quality.

Dry heat

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

Dry heat

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

Examples of dry heat sterilization

Hot air ovens and incineration.

High pressure processing

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 by freezing 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

Destroys microbes by breaking DNA strands.

Non-ionizing radiation

Damages microbial DNA.

HEPA filter

High-efficiency particulate air filters used to remove dust, bacteria, and allergens from the air but do not remove gases or odors.

LifeStraws

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

Intermediate-level disinfectant alcohols

Ethanol and isopropanol, which work by denaturing proteins and disrupting microbial cell membranes.

Disadvantages of using alcohol

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

Aldehydes used in healthcare

Formaldehyde and glutaraldehyde, which kill bacteria and viruses by crosslinking proteins and nucleic acids.

Disadvantages of aldehydes

Aldehydes can be toxic and irritating, requiring careful handling.

Newest aldehyde

Orthophthalaldehyde (OPA), which is less toxic than glutaraldehyde.

Phenols and phenol derivatives

Used as disinfectants in cleaning products and antiseptic formulations.

How phenols work

They denature proteins and disrupt cell membranes.

Disadvantages of phenols

They can be toxic and irritating to the skin.

Examples of halogens

Chlorine, iodine, and bromine.

Halogens

Chlorine, iodine, and bromine.

Halogens' Function

Halogens oxidize and denature microbial proteins. They can be inactivated by organic material or reduced pH.

Most Widely Used Halogen Disinfectant

Chlorine is used for disinfecting drinking water and swimming pools.

Iodine's Effectiveness

Iodine is effective against bacteria, viruses, and fungi.

Examples of Heavy Metals

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 Types of Peroxygens

Hydrogen peroxide and peracetic acid.

Peroxygens at High Concentration

At high concentration, peroxygens are considered high-level disinfectants.

Hydrogen Peroxide Uses

Hydrogen peroxide can be used to disinfect surfaces, wounds, and medical equipment.

Peracetic Acid Effectiveness

Peracetic acid is effective in the presence of organic material.

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

It is toxic, flammable, and requires special handling.

Detergents

Detergents are cleaning agents that damage microbial cell membranes. They work as surfactants and emulsifiers.

Classes of Detergents

Anionic, cationic, and non-ionic detergents.

Bisbiguanides Effect

Bisbiguanides disrupt the microbial cell membrane.

Examples of Bisbiguanides

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

At low temperatures, pressurized carbon dioxide can be used to sterilize medical devices, implants, and transplanted tissues.

Chemical Preservatives

Acetic acid and lactic acid.

Naturally Produced Preservatives

Nisin and natamycin.

Natural Preservative Specificity

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

Factors for Selecting Germicide

Microorganism type, material compatibility, toxicity, and contact time.