EFFECT OF ANTIBIOTICS ON THE GROWTH OF Staphylococcus epidermidis Grace Schofield (Year 10) Science Faculty, The Illawarra Grammar School, Western Avenue, Mangerton, 2500 Abstract In this experiment antibiotic disks consisting of tetracycline, penicillin, ampicillin, chloramphenicol, streptomycin and sulphatriad, were placed on agar plates spread with the bacteria Staphylococcus epidermidis, to determine the effectiveness of antibiotics proven through the zone of inhibition. S. epidermidis was spread on an agar plate and an antibiotic disk was placed on top. To ensure reliability and sanitation, tools used tweezers and inoculation loops were heated with a bunsen burner to rid of any unwanted bacterias. This was repeated another 2 times to ensure reliability. Agar plates were put in an incubator set at 30 degrees for 2 days. The diameter of the zone of inhibition was measured and results concluded which antibiotic was most effective against the growth of S. epidermidis. It was hypothesized that tetracycline, ampicillin, chloramphenicol and penicillin would have larger zones of inhibition as they fight against gram-positive bacteria. Results supported the hypothesis as tetracycline had the largest zone of inhibition (3.9cm) however, results did not support the hypothesis for penicillin as it was essentially non-effective with a zone of inhibition of 0.1cm.
Introduction Bacteria are a small single celled organism found in all types of ecosystems and the human body. Pathogens and parasites are bacteria that cause diseases however, pathogens are very rare, whereas other bacterias are very helpful to the ecosystem and human body, such as bacterias found in a human gut. Staphylococcus epidermidis is a gram positive non-pathogenic bacteria, it is part of human flora typically skin flora, it is a facultative anaerobic bacteria. Bacteria that produces adenosine triphosphate (ATP) by anaerobic respiration if exposed to oxygen however, S. epidermidis is capable of switching to fermentation if oxygen is absent. The zone of inhibition is an area of media where bacteria colonies are unable to grow. The zone of inhibition is measured to determine the effectiveness of antibiotics against bacteria.
Ampicillin, an extended spectrum of penicillin, and tetracycline antibiotics, are active against both gram-positive and gramnegative bacteria therefore, will be effective against S. epidermidis. Chloramphenicol is an antibiotic with a broad spectrum of activity against gram-positive, gramnegative and Rickettsia, hence effective against S. epidermidis. Penicillin works best on gram-positive bacteria through inhibiting peptidoglycan production, which is found in most bacterial cell walls including S. epidermidis. Penicillin fights against peptidoglycan making it effective against S. epidermidis. Streptomycin commonly fights against gram-negative bacteria however, also fights off a small group of bacteria including the staphylococci group, streptomycin is potentially effective against S. epidermidis. Sulphatriad fights against gram-negative bacterias and essentially cannot fight against gram-positive bacteria, 54
