Topic A
The effects of the antibiotic streptomycin (S) and of oreganum essential oil on the bacteria Escherichia coli and Pseudomonas aeruginosa
Oregano essential oil has been found to inhibit food-borne pathogens and spoilage micro-organisms (e.g. Friedman et al 2002) and is therefore of interest to the food industry.
When planning this investigation the student contacted suppliers of antibiotics and arranged to use antibiotics on pre-prepared and standardised paper discs. She carried out two pilot studies to firstly determine how best to apply the oregano oil and secondly used a dilution series on the bacterial species to ensure an appropriate bacterial lawn was obtained on her agar plates. Reading and the pilot study enabled the student to decide how to assess the effect of the potential bactericides. When the discs of treated paper were placed on the agar plate and these then incubated a clear region, the zone of inhibition, was evident. The student decided to measure the diameter of this zone of inhibition.
References
FRIEDMAN, M., HENIKA, P.R., MANDRELL, R.E. (2002). Bactericidal activities of plant essential oils and some of their isolated constituents against Campylobacter jejuni, Escherichia coli, Listeria monocytogenes and Salmonella enterica. Journal of Food Protection, 65(10): 1545 - 1560.
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