Investigating the antibacterial properties of a mouthwash

The mouthwash under test id Asda Protect. It contains:-

· aqua

· alcohol

· glycerin

· polysorbate 20

· sodium benzoate

· aroma

· sodium saccharin

· cetylpyridinium chloride

· menthol

· sodium flouride (0.05%)

In this investigation we aim to test the antibacterial properties of this mouthwash treating it like a disinfectant against three common bacteria which can be safely used in the laboratory: Escherichia coli, Baccilus Megatherium, and Staphlococcus Albus. Disinfection is a procedure which destroys, inactivates or removes potentially harmful microbes- without necessarily affecting other organisms present; it has generally little or no effect on bacterial endospores. Disinfection often refers specifically to the use of other chemical agents (disinfectants) for the treatment of non-living objects or surfaces. Ideally disinfectants for general use should be able to kill a wide range of common or potential pathogens. However, any given disinfectant is usually more effective against some organisms than against others, and the activity of a disinfectant may be greatly affected by factore such as dilution, temperature, pH, or the presence or organic matter or detergent; to be effective at all, a disinfectant needs appropriate conditions, at a suitable concentration, for an adequate period of time. Some disinfectants tend to be unstable, and some need solubilization in order to be effective.

At low concentrations some disinfectants not only cease to be effective, they can actually be metabolized by certain bacteria Dinfectants which kill bacteria are said to be bactericidal. Others merely halt the growth of bacteria, and if such a disinfectant is inactivated – e.g. by dilution, or chemical neutralisation – the bacteria may be able to resume growth; these disinfectants are said to be bacteriostatic. A bactericidal disinfectant may become bacteriostatic when diluted. The mouthwash under test contains substances with disinfectant qualities such as Alcohol, Sodium Flouride and Cetylpyridinium Chloride. Alcohols at concentrations of about 70-80% in water are effective, albeit slowly against vegetative bacteria though not very effective against spores or fungi. Chlorine and Flourine compounds are effective against vegetative bacteria, spores, fungi and both lipid-containing and non lipid-containing viruses. The first bacteria chosen was Escherichia coli (E-coli) from the genus enterobacteriaceae. Its cells are found in pairs or singularly being typically motile and fimbriate. Their optimum temperature for growth is 37C.

This bacteria respires under aerobic conditions and fermentation. E-coli is found in part of the microflora of the human intestine as well as other animals. Some strains are pathogenic. The second bacteria was Baccilus Megatherium belonging to the genus Baccilus. Bacc-Meg is a gram positive bacteria and its cells are rod shaped often 0.5-1.5µm 2-6µm and are typically motile. Bacc-Meg can be either aerobic or facultatively anaerobic as well as being respiratory or facultatively fermentative. It can also grow in nutrient agar. The final bacteria was Staphylococcus Albus belonging to the Staphlococcus genus. It is a gram positive cocci and its cells are 1µm in diameter, often found in clusters, containing an orange or yellow carotenoid pigment. Staph Albus is non-motile and facultatively anaerobic. It is a coagulase negative strain and id found in commensals and pathogens of man and other animals. In order to see how effective the mouthash is against the different bacteria, we will test how different concentrations of the mouthwash will combat a lawn of each bacteria.

Techniques that will be put into pracice are:-

· Melting and pouring agar

· Creating a lawn of bacteria

· Dilutions

· Measuring rings of inhibition

Hypothesis:

The higher the concentration of the mouthwash, the larger the rings of inhibition.