Escherichia coli are rod shaped, gram negative bacteria often found in the gut of humans and other warm-blooded mammals (Jacques & Ngo, 2004). It is transmitted primarily through faecal contaminated food and water. Most strains of E. coli are not harmful to humans, however some strains are pathogenic and can cause symptoms including diarrhoea (Unknown, 2012). The active ingredient in Dettol Antiseptic Liquid is 4.8% chloroxylenol, a chemical that inhibits the growth of a large range of microorganisms including gram negative bacteria. It can be used to cleanse flesh wounds or disinfect surfaces. Chloroxylenol destroys the bacteria by inhibiting the production of adenosine triphosphate. It does so by causing the disruption of cell membrane potentials, destroying the protein gradient essential for the synthesis of ATP (Hertfordshire, 2011). Without ATP cellular functions fail and then die.
Research Question: How does increasing the concentrations of Dettol Antiseptic Liquid from 0% to 100% affect the growth of Escherichia coli bacteria on the agar plates?
Hypothesis: As the concentration of Dettol Antiseptic Liquid increases the inhibition of bacterial growth around the antiseptic disks also increases.
|Type of variable |Variable |How it is controlled | |Independent |The concentration of Dettol applied to the | | | |bacteria. | | |Dependent |The area of inhibited bacterial growth measured | | | |from the edge of the disk to the regular | | | |perimeter of the cleared area. | | |Controlled |Type of antiseptic (active ingredient) |Dettol Antiseptic Liquid with chloroxylenol 4.8%| | |Type and density of bacteria |Two drops of Escherichia coli used to create a | | | |lawn culture for each trial. Performed in | | | |aseptic conditions to avoid contamination. | | |Length of time bacteria exposed to the |Trials left for 48hours before the area of | | |disinfectant |inhibited growth is measured. | | |Environmental factors |Incubated at 37°C for the 48hour period. | | |pH |Same nutrient agar used for all trials. | | |temperature | | | |Contact point of disinfectant |Excess disinfectant removed before placing disks| | | |onto agar plate. | | |Instrument for measurement...