FAQ: Physical and Chemical Control of Microorganisms

• What is sterilization?
• What is a disinfection?
• What is pasteurization?
• What is the difference between an antiseptic and a disinfectant?
• How much heat does it take for sterilization?
• How much heat does it take to properly cook food?
• What are HEPA filters?
• How effective is radiation in destroying microorganisms?
• Should I use consumer products with antibiotics?

» What is sterilization?

The process known as sterilization refers to the process in which all living cells, spores, and viruses are completely destroyed or removed from an object or environment. Once something is sterilized, it will remain sterile if properly sealed. Sterilization is performed on surgical equipment, needles, and certain lab equipment in order to prevent the spread of microorganisms.

Methods used to sterilize objects involve the use of heat, radiation, filtration, and/or chemical means. Autoclaves are devices which use hot steam under high pressure to sterilze objects.

Sterilization is an extreme level of cleanliness that is usually not required outside of a medical, industrial, or laboratory environment. In everyday environments, disinfection of objects is considered a more practical option.

» What is disinfection?

The process known as disinfection is the killing, inhibition, or removal of microorganisms that cause disease. Disinfection may not necessarily eliminate spores or all of the microorganisms from an object or environment. While disinfection is not as extreme as sterilization, but it is considered to be an adequate level of cleanliness for most situations.

» What is pasteurization?

Pasteurization is a process used in preserving heat sensitive foods such as milk, beer, and other beverages. Pasteurization uses mild temperatures (63-66°C for 30 minutes or 71°C for 15 seconds) to kill pathogens and reduce levels of non-pathogenic organisms that cause milk and other foods to spoil. Pasteurization is not a method of sterilzation, which is why pasteurized foods will eventually spoil if given enough time.

A new method called ultrahigh temperature (UHT) sterilization involves heating at 140-150°C for 1 to 3 seconds. Milk that has been treated in this way can be kept at room temperature for 2 months with only minimal changes in flavor.

» What is the difference between an antiseptic and a disinfectant?

Disinfectants are chemical agents used to disinfect inanimate objects and surfaces. Examples of disinfectants include iodine solution, copper sulfate, ozone, and chlorine gas.

Antiseptics are chemical agents applied to living tissues to prevent infection. Antiseptics are generally less toxic than disinfectants because they must not cause too much damage to the host living tissue. Examples of antiseptics include iodine, 70% ethanol and 3% hydrogen peroxide.

The concentration of a chemical agent can determine if it can be used as a disinfectant or an antiseptic. In the case of iodine, weaker solutions of iodine can be used for antiseptic purposes, while stronger concentrations should be used as a disinfectant.

» How much heat does it take to destroy microorganisms?

Moisture improves heat penetration, making sterilization by moist heat more effective then dry heat. Killing microorganisms by dry heat is a lengthy process that requires high temperatures. On the other hand, most yeasts, molds, and bacteria can be killed using moist heat at 80°C for 10 minutes. These conditions are not sufficient to inactivate mold or bacteria spores, which are more heat-resistant than cells in their vegetative states.

Bacterial spores require exposure to moist heat at temperatures of 121°C (achieved under high-pressure conditions) for at least 15 minutes for inactivation. The "gold standard" for heat sterilizatin is inactivation of Bacillus stearothermophilus spores. If heat treatment was sufficient to inactivate test strips containing these spores, then the sterilization is considered successful.

It is important to note that there are rare types of bacteria which are capable of growing at high temperatures. These bacteria are classified as thermophiles and hyperthemophiles. Bacillus stearothermophilus is a thermophile. These organisms normally growth in unusually hot environments, including hot springs and deep-sea vents. Clearly sterilization by heat may not be the most efficient method to eliminate these types of bacteria, but they are almost never found in common environments.

» How much heat does it take to properly cook food?

Proper storage of food requires refrigeration (5°C) or freezing below the temperatures that at microorganisms normally grow. Proper cooking requires that the temperature at the centre of the meat reaches the following temperatures:

It is important to note that certain pathogens produce heat-stable exotoxins that are still present after cooking at the proper temperatures. Food can also be contaminated after it has been cooked, by kitchen utensils or hands that have not been properly washed.

» What are HEPA filters?

HEPA filters are High-Efficiency Particulate Air filters designed for the filtration of small particles. Certified HEPA filters must capture a minimum of 99.97% of 0.3 microns contaminants. HEPA air filters are used in hospital operating rooms, isolation rooms, biocabinets, and pharmaceutical manufacturing facilities. Filtration is the primary method of eliminating pathogens from the air supply.

» How effective is radiation in destroying microorganisms?

The most lethal type of radiation is ultraviolet radiation with a wavelength of 260 nm. This is the wavelength most actively absorbed by DNA. Unfortunately, this type of radiation does not penetrate dirt, glass, water, or other substances. If a surface is dusty, then complete inactivation of all microorganisms may not occur. This type of radiation is also harmful if someone is directly exposed to it, as it may damage the skin and eyes. Due to its poor penetration, UV radiation is only useful for disinfecting outer surfaces.

Ionizing radiation (gamma radiation) can penetrate deeper into objects, and is used to sterilize food, drugs, and medical supplies. The source of these gamma rays is usually cobalt-60 which has a half-life of 5 years. Materials which are sterilized using this type of radiation do not become radioactive, and irradiation of food does not change its nutritional value. In some cases the taste of the food is changed, similar to how milk changes taste once it is pasteurized.

» Should I use consumer products that contain antibiotics?

In the last few years, there have been a number of cleaning products introduced which contain antibiotics. These products include hand lotions, soaps and body washes. There is a growing concern that widespread unnecessary use of antibiotics will result in an increase in antibiotic resistant organisms.

There are some factors that consumers might want to consider before using consumer products that contain antibiotics. Each antibiotic has its own spectrum of efficiency, meaning that the antibiotic will be effective against certain types of bacteria and ineffective against others. Antibiotics are also completely ineffective against viruses, such as Norwalk virus and influenza. Antibiotic-based cleaning solutions will lose their efficiency faster than their chemical equivalents, since antibiotics are complex molecules that can degrade.