FAQ: Physical and Chemical Control of Microorganisms
» 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
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
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:
Minimum Safe Internal
|Poultry (dark meat)
|Poultry (light meat)
|Ground Beef and All Types of Pork
|Beef, veal, lamb, steak, and chops (medium rare)
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
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.
This website has been made possible through an unrestricted educational grant from
Pfizer Canada Inc.