Lesson 13: CONTROL OF MICROORGANISIMS Flashcards
Two goals of controlling microorganisms
a. to destroy pathogens and prevent their transmission and
b. to reduce or eliminate microorganisms responsible for the contamination of water, food, and other substances.
a process by which an article, surface, or medium is freed of all living microorganisms either in the vegetative or in the spore state.
Sterilization
Microorganisms are controlled
either by
a. physical agents (temperature, desiccation, osmotic pressure, radiation, and filtration)
b. chemical agents (disinfectants, antiseptics, antibiotics, and chemotherapeutic antimicrobial chemicals)
any material that has been subjected to sterilization
Sterile
a chemical agent that is used to perform sterilization because of their ability to destroy spores
Sterilants
: also called a microbicide, is any chemical agent that kills pathogenic microorganisms either on inanimate (nonliving) materials or on living tissue but not resistant microbial
Germicide
the use of a chemical agent that destroys or removes all pathogenic organisms or organisms capable of giving rise to infection or its harmful products (toxin) thus destroys vegetative pathogens but not bacterial endospores. Used only on inanimate objects because they can be toxic to human and other animal tissue, when used in higher concentrations.
Disinfection
is defined as the growth of microorganisms in the body or the presence of microbial toxins in blood and other tissues.
sepsis
refers to any practice that prevents the entry of infectious agents into sterile tissues and thus
Asepsis
are chemical agents applied directly to the exposed body surfaces (e.g., skin and mucous membranes), wounds, and surgical incisions to destroy or inhibit vegetative pathogens.
Antiseptics
a process usually involves scrubbing the skin or immersing it in chemicals, or both. It also emulsifies oils that lie on the outer cutaneous layer and mechanically removes potential pathogens from the outer layers of the skin.
degerming/Antisepsis
a compound (e.g., soap or detergent) that is used to perform sanitization. Air sanitization with ultraviolet lamps reduces airborne microbes in hospital rooms, veterinary clinics, and laboratory installation.
Sanitizer
is any cleansing technique that mechanically removes microorganisms (along with food debris) to reduce the level of contaminants.
Sanitation
Examples of degerming procedures are
a. surgical hand scrub
b. application of alcohol wipes to the skin, and
c. cleansing of a wound with germicidal soap and water.
Methods of controlling microorganisms
- Sterilization
- Disinfection
- Antimicrobials
Physical methods of sterilization
- Sunlight
- Heat
- Filtration
- Radiation
- Sonication
STERILIZATION
Classified into:
- Physical methods
- Chemical
a natural method of sterilization of water in tanks, rivers, and lakes. It has an active germicidal effect due to its content of ultraviolet and heat rays. Bacteria present in natural water sources are rapidly destroyed by exposure.
Sunlight
one of the most dependable method of sterilization. As a rule, higher temperatures (exceeding the maximum) are microbicidal, whereas lower temperatures (below the minimum) tend to have inhibitory or microbiostatic effects.
Heat
Rule of temperature
Higher is microbicidal while lower have inhibitory or microbiostatic effects.
Two types of sterilization
Moist and dry
occurs in the form of hot water, boiling water, or steam (vaporized water) and the temperature usually ranges from 60 to 135°C. Moist heat kills microorganisms by denaturation and coagulation of proteins.
Moist heat sterilization
Moist heat sterilization temperature usually ranges
from 60°C to 135°C
Classification of moist heat:
- Sterilization at a temperature below 100°C
- Sterilization at a temperature of 100°C
- Sterilization at a temperature above 100°C
- Intermittent sterilization
example is Pasteurization
Sterilization at a temperature below 100°C
a technique in which heat is applied to liquids to kill potential agents of infection and spoilage, while at the same time retaining the liquid’s flavor and food value. This method is extensively used for sterilization of milk and other fresh beverages, such as fruit juices, beer, and wine which are easily contaminated during collection and processing.
Pasteurization
Pasteurization has two methods
Flash method and holder method
product is exposed to heat at 72°C for 15–20 seconds followed by a sudden cooling to 13°C or lower
Flash method
product is exposed to a temperature of 63°C for 30 minutes followed by cooling to 13°C or lower, but not less than 6°C
Holder method
inactivates most viruses and destroys the vegetative stages of 97–99% of bacteria and fungi, it does not kill endospores or thermoduric species (mostly nonpathogenic lactobacilli, micrococci, and yeasts
Pasteurization
includes (a) boiling and (b)
steam sterilizer
Sterilization at a temperature of 100°C
Health and commercial industries use an autoclave for this purpose and a comparable home appliance is the pressure cooker.
Sterilization at a temperature above 100°C
Simple 10–30 minutes kills most of the vegetative forms of bacteria but not bacterial spores thus only for disinfection.
Boiling
substances are exposed to steam at atmospheric pressure for 90 minutes during which most vegetative forms of the bacteria except for the thermophiles are killed by the moist heat.
Steam sterilizer at 100°C
Certain heat-labile substances (e.g., serum, sugar, egg, etc.) that cannot withstand the high temperature of the
autoclave can be sterilized by a process of intermittent sterilization, known as
Tyndallization
used most often to sterilize heat-sensitive culture media, such as those containing sera (e.g., Loeffler’s serum slope), egg (e.g., Lowenstein–Jensen’s medium), or carbohydrates (e.g., serum sugars) and some canned foods.
Intermittent sterilization
carried out over a period of 3 days and requires a chamber to hold the materials and a reservoir for boiling water. Items to be sterilized are kept in the chamber and are exposed to free-flowing steam at 100°C for 20 minutes, for each of the three consecutive days.
Tyndallization
makes use of air with a low moisture content that has been heated by a flame or electric heating coil. In practice, the temperature of dry heat ranges from 160°C to several thousand degrees Celsius. The dry heat kills microorganisms by protein denaturation, oxidative damage, and the toxic effect of increased level of electrolytes.
Dry heat Sterilization
The surviving spores are allowed to germinate to vegetative forms on the second day and are killed on re-exposure to steam.
2nd day
the temperature is adequate to kill all the vegetative forms of the bacteria, yeasts, and molds but not sufficient to kill spores
1st day
re-ensures killing of all the spores by their germination to vegetative forms.
3rd day
Sterilization of inoculating loop or wire, the tip of forceps, searing spatulas, etc., is carried out by holding them in the flame of the Bunsen burner till they become red hot. Glass slides, scalpels, and mouths of culture tubes are sterilized by passing them through the Bunsen flame without allowing them to become red hot.
Flaming
an excellent method for safely destroying infective materials by burning them to ashes
Incineration
electrically heated and is fitted with a fan to ensure adequate and even distribution of hot air in the chamber. It is also fitted with a thermostat that ensures circulation of hot air of desired temperature in the chamber.
Hot air oven
