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    An agent used to reduce the number of bacteria on a toilet would most accurately is called disinfectant. Disinfectant is the chemical substances that can reduce the microbial load from non-living surfaces. It is used for the sterilization of inanimate surfaces.

    The properties of  the perfect disinfectant are as follows:

    • It should provide the purpose of whole sterilization.
    • It should not provide any health harm to human and other organism.
    • It should be inexpensive and non-corrosive.
    • It should not mix with other chemical and no chemical reaction occurs.
    • It should be safe.

    Factors affecting the choice of disinfectant:

    There are many factors that are used to select the disinfectant.

    1. Chemical agent properties:

    The disinfectant properties should be determined. It includes the nature of disinfectant, the toxicity of disinfectant, temperature and pH of disinfectant, activity in the presence of organic matter and chemicals.  Concentration coefficient is also calculated. It is the decrease in the activity of the disinfectant when we dilute the disinfectant.

    1. Microbial challenge:

    It is an important factor for the selection of disinfectant. The microbial load is directly proportion to the disinfectant used. For the disinfectant selection, the order of microbial load sensitivity against disinfectant are

    Vegetative bacteria < mycobacterium tuberculosis < spores < fungi < viruses < protozoa < prions.

    1. Intended application:

    Intended application refer to those process that disinfectant is not absorb by the product or material e.g. QAC are absorbed by the fabrics. Disinfectants only remain on the non-living surfaces and then wash out.



    1. Environmental factors:

    Environment is also a factor to select any disinfectant. it refers to the media in which microbes grow. It may be air, liquid or solid.

    Factors affecting antimicrobial activity:

    There are many factors that affect the antimicrobial activity of the disinfectant.

    1. Innate resistant of microbes:

    Some microbes are naturally resistant to the disinfectant. They don’t respond to the disinfectant and continues dividing. E.g. spores are resistant to ethanol.

    1. Microbial diversity:

    The more the microbes present on the surface, the more difficult is to clean them. The number of microbes present on the surface is directly proportion to the amount of disinfectant.

    1. Concentration coefficient:

    Concentration coefficient is the number in which the disinfectant activity is reduced on dilution.

    1. Exposure time:

    Exposure time also effect the disinfectant activity. The maximum time is required so that all the microbes get exposed to the disinfectant and sterilization take place.

    1. Physico-chemical conditions:

    Temperature, pH, humidity, moisture and presence of other organic matter also affect the activity of disinfectant. These may lower the activity of disinfectant.

    Types of disinfectant:

    There are three types of disinfectant.

    1. Low type of disinfectant:

    This type of disinfectant has less activity. Most of the vegetative bacteria, fungi die but mycobacterium tuberculosis, spores, prions and viruses remain alive.

    1. Intermediate type of disinfectant:

    This type of disinfectant has intermediate activity. Most of the vegetative bacteria, fungi, mycobacterium tuberculosis, and hepatitis B virus die while spores, prions remain alive.


    1. High level of disinfectant:

    This type of disinfectant has highest activity against microbes. All the life forms die while prions remain alive, as they are the most resistant and infectious form of proteins.

    Disinfectant examples:

    Sodium hypochlorite:

    Sodium hypochlorite is the strong oxidizing agent that oxidizes the protein. When protein oxidizes, it denatures and metabolism stops. The stop metabolism causes the death of bacteria and other organism. It can kill all types of micro-organism (including spores). It is less expensive and it is not affected by hard water. But, its activity is totally depends on the pH.


    Chlorine is also an oxidizing agent that oxidized the cell. It is used in the form of chlorine dioxide for reducing the microbial load from water systems and it is also being used in the surface disinfection in CIP. It is commonly used because it is a broad spectrum disinfectant that gives activity even at low concentrations. It has rapid microbiological killing action. It does not form ecotoxic compound by reacting with organics.

    Hydrogen peroxide:

    Hydrogen peroxide is also strong oxidizing agent. It kills all life forms on the surface. The disadvantage is that it not safe to use. It is commonly used for disinfection of product packs prior to aseptic filling in the beverage industry.


    Iodophore is also an oxidizing agent that is produced by dissolving iodine in an acid medium. It has many advantages

    • It kills a wide range of organisms at low temperatures
    • It have short contact time
    • It can cope with hard water

    Quaternary ammonium compound:

    They have strong bactericidal effect. They bind irreversibly to the proteins and phospholipids. This makes the membrane permeable and then the disinfectant moves inside and destroys the cell. It also denatures the enzymes and proteins. Thus cell death occurs. They are less effective against gram negative, spores and viruses. For the sterilization of fungi, high concentration of disinfectant is used.

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