Determine Disinfectant and Antiseptic Effectiveness Using Zone Inhibition Method

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Determine Disinfectant and Antiseptic Effectiveness Using Zone Inhibition Method
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This study is to examine the effects of different types of disinfectants by disk diffusion method using common agents such as Betadine, Clorox, Crest, Kiss My Face, Listerine, and Lysol. Wound care and general cleaning of home surfaces is a part of daily activity for many of the general population. Knowing which agents are effective against the bacteria that most commonly cause infection, disease, and illness allows educated decisions on which agents to use. We compared the bactericidal effectiveness of 6 common agents widely used by the general public against 3 common bacterial organisms.

Sterilization kills all organisms in or on an object or substance. Disinfectants and antiseptics do not sterilize since many types of organisms and spores are not killed. Disinfectants are described as antimicrobial agents that are used on inanimate objects such as an instrument or structural surfaces. The term antiseptic is usually applied to antimicrobial agents that are used on living tissue such as skin and throat mucosa.

A disinfectant must be capable of killing pathogens while it is in contact with them, so that they cannot grow again when it is removed. This action is said to be cidal (lethal), and it is described according to the type of organisms it kills as bactericidal, sporicidal, fungicidal, virucidal, etc… If the antimicrobial substance merely inhibits the organisms while it is in contact with them, they may be able to multiply again when it is removed. In this case, the agent is said to have static activity and may be described as bacteriostatic, fungistatic, etc…

Microorganisms of different groups are not uniformly susceptible to chemical disinfection due to the structures of their cell walls. As an example, Mycobacterium are more resistant than most other bacteria because of their waxy cell walls. Of all microbial forms, bacterial endospores display the greatest resistance to both chemical and physical agents of disinfection. The efficacy claimed for a given disinfectant in killing vegetative bacterial species may have no bearing on its ability to destroy bacterial or fungal spores, mycobacteria, some viruses or prions.

A number of factors must be considered when choosing a disinfectant besides type of organism. These include exposure time, concentration of the antimicrobial agent, temperature, optimal pH activity of the antimicrobial agents, the concentration of the microorganisms present, and the toxicity of the agent for skin or its effect on materials to be disinfected.

Here we will test the effectiveness of various antimicrobial substances by inoculating culture plates with the test organisms and then applying the disinfectant/antiseptic to the inoculated plate by a filter paper disk that has been dipped into the disinfectant/antiseptic. This is a disk diffusion method that is similar to the method used to test the effectiveness of various chemotherapeutic agents. We will then measure the zone-of-inhibition. With this method, the presence of such a clear zone (lack of growth) surrounding the chemical shows either the cells have been killed or that their growth has been inhibited. A zone of inhibition does not discriminate between bacterio-static and bactericidal chemicals.

The 6 agents we will be testing are:
Betadine (B) – A povidone-iodine preparation used mainly for skin disinfection and wound treatment. Kills a wide range of disease-causing organisms including bacteria, fungi, many viruses, and most micro-organisms. Does not affect hydrophilic viruses such as polyomavirus and PBFD. Clorox (C) – A biguanide preparation of Sodium Hypochlorite used mainly for surface cleaning in various environments such as homes and hospitals to kill microorganisms. Bleach is effective as...
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