LESSON 13: CONTROL MICROORGANISM Flashcards
Ubiquitous and many microorganisms are associated with
undesirable consequences, such as food spoilage and disease.
MICROBES
it is essential to kill a wide variety of microorganisms or inhibit their growth to minimize
their destructive effects. The goal is twofold:
: (a) to destroy pathogens and prevent
their transmission and
(b) to reduce or eliminate microorganisms responsible for the
contamination of water, food, and other
Microorganisms are controlled
either by
physical agents (temperature, desiccation, osmotic pressure, radiation, and
filtration) or
Chemical agents (disinfectants, antiseptics, antibiotics, and chemotherapeutic antimicrobial chemicals).
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
any material that has been subjected to the above process.
Sterile
A chemical agent that is used to perform sterilization because of their ability y 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.
Disinfection
Used only on inanimate objects because they can be toxic to human and other animal tissue, when used in HIGHER CONCENTRATION
Disinfectant
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
s any cleansing technique that mechanically removes
microorganisms (along with food debris) to reduce the
Sanitization
e 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
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 installations.
Sanitizer
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
STERILIZATION
Classified into:2.
1. Physical methods
2. Chemical method
Methods of controlling microorganism
- Sterilization
- Disinfection
- Antimicrobials
Physical methods of sterilization
- Sunlight
- Heat
- Filtration
- Radiation
- Sonication
natural method of sterilization of water in tanks, rivers, and lakes.
Sunlight
Direct sunlight 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 to sunlight.
One of the most dependable method of sterilization.
Heat
higher
temperatures (exceeding the maximum) are microbicidal, whereas
lower
temperatures (below the minimum) tend to have inhibitory or microbiostatic
effects.
Two types:
moist and dry heat.
Sterilization by moist heat occurs
Hot water, boiling water, or
steam (vaporized water) and the temperature usually ranges from 60 to
135°C. M
Moist heat kills microorganisms by
denaturation and coagulation of
proteins.
Classification of moist heat:
Sterilization at a temperature below 100°C: example is Pasteurization
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.
Pasteurization
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
Pasteurization 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)
Sterilization at a temperature of 100°C: includes
(a) boiling and
(b) steam sterilizer
Of water for 10–30 minutes kills most of the vegetative forms of bacteria but not bacterial spores thus only for disinfection.
Boiling
At 100°C: 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
pasteurization 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).
Sterilization at a temperature above 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
Process of Tyndallization
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 to flowing steam at 100°C for 20 minutes, for each of the three consecutive
days
1st day:
: the temperature is adequate to kill all the vegetative forms of the
bacteria, yeasts, and molds but not sufficient to kill
2nd day:
The surviving spores are allowed to germinate to vegetative
forms on the second day and are killed on re-exposure to steam.
3rd day:
Re-ensures killing of all the spores by their germination to
vegetative forms
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.
Sterilization by dry heat
kills microorganisms by protein denaturation, oxidative damage, and the toxic effect of increased level of electrolytes.
Dry heat
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.
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.
Hot air oven
remove contaminating microorganisms from solutions rather than
directly destroying them.
Filters
The filters are of two types:
(a) depth filters;
ex: candle filter, asbestos filter or sintered glass filters
(b) membrane filters;
ex: cellulose acetate, cellulose nitrate, polycarbonate, polyvinylidene fluoride, or other
synthetic materials made
An excellent sterilizing agent
with very high penetrating power.
These radiations penetrate deep into objectsand destroy bacterial endospores and vegetative cells, both prokaryotic and
eukaryotic but not that effective against viruses.
Example: (a) X-rays, (b) gamma
rays, and (c) cosmic rays
from a cobalt-60 source is 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
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.”
While nonionizing radiations include infrared and
Use of high-frequency sound (sonic) waves beyond the sensitivity
of the human ear are known to disrupt cells. Sonication transmits vibrations
through a water-filled chamber (sonicator) to induce pressure changes and create intense points of turbulence that can stress and burst cells in the vicinity.
Sonication
Heat generated by the sonic waves (up to 80°C) also appears to contribute to the antimicrobial
action.
Gram-negative rods are most sensitive to ultrasonic vibrations.
Gram-positive cocci, fungal spores, and bacterial spores are resistant to them
The process of inactivating microorganisms by direct exposure to chemical or
physical agents.
DISINFECTION
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.
are biocides or products that destroy
or inhibit the growth of microorganisms
Antiseptics
9 Properties of ideal disinfectant
- It should have a wide spectrum of antimicrobial activity.
- It should act in the presence of organic matter.
- It should not be toxic to human or corrosive.
- It should be stable upon storage and should not undergo any chemical
change. - It should be odorless or with a pleasant odor.
- It should be soluble in water and lipids for penetration into microorganisms.
- It should be effective in acidic as well as in alkaline media.
- It should have speedy action.
- If possible, it should be be relatively inexpensive.
Action of Disinfectants
- They produce damage to the cell wall and alter permeability of the cell
membrane, resulting in exposure, damage, or loss of the cellular contents. - They alter proteins and form protein salts or cause coagulation of proteins.
- They inhibit enzyme action and inhibit nucleic acid synthesis or alter nucleic
acid molecules. - They cause
Factors Influencing Activity of Disinfectants
- temperature
- types of microorganism
- physiological state of the cell
- environment
- temperature
Increase in temperature increases the efficiency of
disinfectants.
Vegetative cells are more susceptible than spores.
Spores may be resistant to the action of disinfectants.
Type of microorganism:
: Young and metabolically active cells are more
sensitive than old dormant cells. Non growing cells
. Physiological state of the cell:
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
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. E
Examples
- phenol
- Crerol
- Halogenated diphenyl compounds
is effective against
vegetative forms of bacteria but not suitable for application to skin or mucous
membrane),
Phenol
(are 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
is a solution of cresols in soap)
Lysol
s (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 longer
periods.
It can cause brain damage and is now used in hospital
nurseries only after a staphylococcal outbreak)
Are fluorine, bromine, chlorine, and iodine—a group of
nonmetallic elements that commonly occur in minerals, sea water, and salts.
Halogens
kills not only bacterial cells and endospores but also fungi and viruses
chlorine
at a concentration of 0.6–1.0 part of chlorine per million parts of
water makes water potable and safe to use.
Chlorination
chlorine is ineffective at
an alkaline pH, less effective in the presence of excess organic matter,
and
relatively unstable, if exposed to light.
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.
not adversely affected by organic matter and
pH.
Iodine
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.
alcohol
are the two most
popular alcohol germicides.
They act by denaturing bacterial proteins and
possibly by dissolving membrane lipids.
Ethyl alcohol
Isopropyl alkohol
Is effective against fungal spores.
Methyl 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.
Folmaldehyde
Is 40% aldehyde in aqueous
solution.
It is used to:
1. preserve fresh tissue specimens,
2. destroy anthrax spores
in hair and wool,
3. prepare toxoids from toxins,
4. sterilize bacterial vaccines, and
5. kill bacterial cultures
Formalin Solution
used for sterilization of large volume of heat-sensitive disposable
items and also instruments
Gases
frequently used gaseous agents
Ethylene oxide,
formaldehyde gas, and
betapropiolactone
: such as detergents are the substances that alter
energy relationship at interfaces producing a reduction in surface tension.
are 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
Surface active agents:
They are different from soaps, which are
derived from fats. Four types:
: (i) Cationic surface active agents ex: quaternary
ammonium compounds,
(ii) Anionic surface active agents, ex: soap made from
saturated or unsaturated fatty acids,
(iii) Nonionic surface active agents (not
effective),
(iv) Amphoteric or ampholytic compounds
This group 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
used extensively as skin and wound antiseptics include
(a) acridine
dyes and
(b) aniline dyes both more active against Gram positive bacteria
Dyes
Soluble salts of mercury, silver, copper, arsenic, and other
heavy metals 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:
(such as sulfuric acid, nitric acid, hydrochloric acid, and benzoic acid) a
acids
(like potassium and sodium hydroxide and
ammonium hydroxide) are germicidal in nature.
alkalis
They kill microorganisms by
hydrolysis and altering the medium
acids and alkalis
