Lesson 13: CONTROL OF MICROORGANISIMS Flashcards by Jamismark Perante

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.

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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

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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)

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any material that has been subjected to sterilization

Sterile

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a chemical agent that is used to perform sterilization because of their ability to destroy spores

Sterilants

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: 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

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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

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is defined as the growth of microorganisms in the body or the presence of microbial toxins in blood and other tissues.

sepsis

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refers to any practice that prevents the entry of infectious agents into sterile tissues and thus

Asepsis

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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

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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

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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

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is any cleansing technique that mechanically removes microorganisms (along with food debris) to reduce the level of contaminants.

Sanitation

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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.

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Methods of controlling microorganisms

Sterilization
Disinfection
Antimicrobials

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Physical methods of sterilization

Sunlight
Heat
Filtration
Radiation
Sonication

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STERILIZATION
Classified into:

Physical methods
Chemical

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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

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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

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Rule of temperature

Higher is microbicidal while lower have inhibitory or microbiostatic effects.

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Two types of sterilization

Moist and dry

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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

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Moist heat sterilization temperature usually ranges

from 60°C to 135°C

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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

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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

1. damage and alter permeability of the cell membrane 2. alter proteins and form protein salts or cause coagulation of proteins. 3. inhibit enzyme action and inhibit nucleic acid synthesis or alter nucleic acid molecules. 4. They cause oxidation or hydrolysis

Properties of ideal disinfectant

1. wide spectrum of antimicrobial activity. 2. act in the presence of organic matter. 3. not toxic to human or corrosive. 4. stable upon storage and should not undergo any chemical change. 5. odorless or with a pleasant odor. 6. soluble in water and lipids for penetration into microorganisms. 7. effective in acidic as well as in alkaline media. 8. speedy action. 9. relatively inexpensive

Factors Influencing Activity of Disinfectants

1. Temperature 2. Type of microorganism 3. Physiological state of the cell 4. 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

1. Phenolic compounds 2. Halogens 3. Alcohols 4. Aldehydes 5. Gases 6. Surface active agent 7. Oxidizing agents 8. Dyes 9. Heavy metals 10. 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

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