Antibiotic Synergism and Antagonism by Skin Bacterium Staphylococcus epidermidis, Staphylococcus simulans, and Citrobacter freundii

by Austin Ferguson, Tanner Urich, and Jacklyn Johnson
Faculty advisor: Dr. Brian Lenzmeier

Bacterial resistance to antibiotics is a growing medical concern. We are studying the effects of different antibiotics on the viability of the naturally occurring skin bacterium Staphylococcus epidermidis and Staphylococcus simulans. Because of the high rate of resistance of bacteria to single antibiotics it is of interest to determine which combinations of antibiotics may be useful in killing bacteria. Specifically, we are interested in determining which combinations of antibiotics work synergistically or antagonistically. Synergistic combinations work better together at lower dosages than using only one antibiotic at a higher dose. Antagonistic combinations work less effectively when given together than they would when taken individually. Two years ago we screened a panel of seven antibiotics for the best synergistic combinations. Last semester we began using liquid cultures of the bacterium and are using three different antibiotic combinations to more closely mimic physiological conditions. We currently are testing for the lowest concentrations of antibiotics that have the ability to work synergistically in killing S. epidermidis and S. simulans. We will be presenting are results and our future plans of the research.