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
remove contaminating microorganisms from solutions rather than directly destroying them.
Filtration
The filters are of two types:
depth filters
ex candle filter, asbestos filter or sintered glass filters
depth filters
an excellent sterilizing agent with very high penetrating power. These radiations penetrate deep into objects and destroy bacterial endospores and vegetative cells, both prokaryotic and eukaryotic but not that effective against viruses.
Ionizing radiations
ex, cellulose acetate, cellulose nitrate, polycarbonate, polyvinylidene fluoride, or other synthetic materials.
membrane filters
examples of Ioonizing radiations
a. X-rays
b. gamma rays
c. cosmic rays.
used for sterilization of antibiotics, hormones, sutures, catheters, animal feeds, metal foils, and plastic disposables, such as syringes, meat and other food items.
Gamma radiation from a cobalt-60 source
Irradiation usually kills
Escherichia coli O157:H7,
Staphylococcus aureus,
Campylobacter jejuni,
and other pathogens.
Since there is no detectable increase of temperature in this method, this method is commonly referred to as “cold sterilization.” Both the Food and Drug Administration and the World Health Organization have approved food irradiation
Radiation
Heat generated
by the sonic waves
up to 80°C
nonionizing radiations include
infrared and ultraviolet radiations
Use of high-frequency sound (sonic) waves beyond the sensitivity of the human ear are known to disrupt cells. transmits vibrations through a water-filled chamber to induce pressure changes an create intense points of turbulence that can stress and burst cells in the vicinity. Also forcefully dislodges foreign matter from objects.
Sonication
also appears to contribute to the antimicrobial action.
Heat generated
by the sonic waves
most sensitive to ultrasonic vibrations
Gram-negative rods
resistant to ultrasonic vibration
Gram-positive cocci
fungal spores, and
bacterial spores
Water-filled chamber where sonication transmit vibration
Sonicator
The process of inactivating microorganisms by direct exposure to chemical or physical agents.
Disinfection
Reversible inhibition of spore germination
Sporistatic
products or biocides that destroy or inhibit the growth of microorganisms on inanimate objects or surfaces. Disinfectants can be sporistatic but are not necessarily sporicidal.
Disinfectant
Tending to kill spores
sporicidal
biocides or products that destroy or inhibit the growth of microorganisms in or on living tissue.
Antiseptics
Action of Disinfectant
- damage and alter permeability of the cell membrane
- alter proteins and form protein salts or cause coagulation of proteins.
- inhibit enzyme action and inhibit nucleic acid synthesis or alter nucleic acid molecules.
- They cause oxidation or hydrolysis
Properties of ideal disinfectant
- wide spectrum of antimicrobial activity.
- act in the presence of organic matter.
- not toxic to human or corrosive.
- stable upon storage and should not undergo any chemical change.
- odorless or with a pleasant odor.
- soluble in water and lipids for penetration into microorganisms.
- effective in acidic as well as in alkaline media.
- speedy action.
- relatively inexpensive
Factors Influencing Activity of Disinfectants
- Temperature
- Type of microorganism
- Physiological state of the cell
- Environment
Increase of this increases the efficiency of disinfectants.
Temperature
Vegetative cells are more susceptible than spores. Spores may be resistant to the action of disinfectants.
Types of organisms
The physical or chemical properties of the medium or substance influence rate as well as efficiency of disinfectants, e.g., pH of the medium and presence of extraneous materials
Environment
Types of Disinfectant
- Phenolic compounds
- Halogens
- Alcohols
- Aldehydes
- Gases
- Surface active agent
- Oxidizing agents
- Dyes
- Heavy metals
- Acid and alkalis
Young and metabolically active cells are more sensitive than old dormant cells. Non growing cells may not be affected.
physiological state of the cell
chemical that kills fungus
Fungicidal
Examples of halogenated diphenyl compound
Hexachlorophene and Chlorhexidine
most widely used antiseptics and disinfectants in laboratories and hospitals worldwide. They are bactericidal or bacteriostatic and some are fungicidal also. They act by denaturing proteins and disrupting cell membranes. They are effective in the presence of organic material and remain active on surfaces long after application.
Phenolic compounds
Examples of Phenolic compounds
Phenol
Cresol
Halogenated diphenyl compounds
A halogen that kills not only bacterial cells and endospores but also fungi and viruses.
Chlorine
a solution of cresols in soap
Lysol
effective against vegetative forms of bacteria but not suitable for application to skin or mucous membrane
Phenol
more germicidal and less poisonous than phenol but corrosive to living tissues. They are used for cleaning floors (1% solution), for disinfection of surgical instruments, and for disinfection of contaminated objects
Cresol
like hexachlorophene and chlorhexidine are highly effective against both Gram- positive and Gram-negative bacteria. They are used as skin antiseptics and for the cleaning of wound surfaces especially hexachlorophene because once applied it persists on the skin and reduces growth of skin bacteria for longe periods. However, it can cause brain damage and is now used in hospital nurseries only after a staphylococcal outbreak.
Halogenated diphenyl compounds
fluorine, bromine, chlorine, and iodine—a group of nonmetallic elements that commonly occur in minerals, sea water, and salts.
Halogens
Chlorine concentration that still makes water potable and safe to use.
0.6–1.0 part of chlorine per million parts of water
ineffective at an alkaline pH, less effective in the presence of excess organic matter, and relatively unstable, if exposed to light.
Chlorine
rapidly penetrates the cells of microorganisms, where it apparently disturbs a variety of metabolic functions by interfering with the hydrogen and disulfide bonds of proteins (similar to chlorine). But not adversely affected by organic matter and pH.
Iodine
The two primary iodine preparations
free iodine in solution and
iodophors (betadine).
most widely used disinfectants and antiseptics effective at a concentration of 60–70% in water. They are bactericidal and fungicidal but not sporicidal or virucidal.
Alcohols
effective against fungal spores.
Methyl alcohol
the two most popular alcohol germicides
Ethyl alcohol and isopropyl alcohol
They act by denaturing bacterial proteins and possibly by dissolving membrane lipids. They are used as skin antiseptics.
Ethyl alcohol and isopropyl alcohol
are highly reactive molecules that combine with nucleic and alkylating molecules; sporicidal and can be used as chemical sterilants.
Aldehydes
that is usually dissolved in water or alcohol before use against bacteria, spores and viruses.
Formaldehyde
It is used to: preserve fresh tissue specimens, destroy anthrax spores in hair and wool, prepare toxoids from toxins, sterilize bacterial vaccines, and kill bacterial cultures and suspensions.
Formalin solution
Formalin solution
40% aldehyde in aqueous
solution
used for sterilization of large volume of heat-sensitive disposable items and also instruments.
Gases
frequently used gaseous agent
Ethylene oxide
formaldehyde gas
and betapropiolactone
such as detergents are the substances that alter energy relationship at interfaces producing a reduction in surface tension.
Surface active agents
organic molecules that serve as wetting agents and emulsifiers because they have both polar hydrophilic and nonpolar hydrophobic ends thus are very effective cleansing agents. They are different from soaps, which are derived from fats.
Detergents
example of Anionic surface active agents
soap made from saturated or unsaturated fatty acids
Four types of surface active agents
(i) Cationic surface active agents
(ii) Anionic surface active agents
(iii) Nonionic surface active agents (not
effective)
(iv) Amphoteric or ampholytic compounds
Oxidizing agents includes
halogens
hydrogen peroxide
potassium permanganate, and
sodium perborate.
They are good disinfectants and antiseptics but are less effective in the presence of organic matter
Oxidizing agents
example of Cationic surface active agents
quaternary ammonium compounds
used extensively as skin and wound antiseptics include (a) acridine and (b) aniline both more active against Gram positive bacteria.
Dyes
Dyes includes
(a) acridine dyes and
(b) aniline dyes
have antibacterial activity, both bactericidal and bacteriostatic. They combine with proteins, often with their sulfhydryl groups and inactivate them or may also precipitate cell proteins.
Heavy metals
They kill microorganisms by
hydrolysis and altering the pH of the medium.
Acids and alkalis
Heavy metals includes
Soluble salts of mercury, silver, copper, arsenic, and other
Alkalis disinfectant
potassium and sodium hydroxide and
ammonium hydroxide
Acid disinfectant
sulfuric acid
nitric acid
hydrochloric acid
benzoic acid
