An Investigation of the Synergistic Effects of Procaine G Penicillin and Oxytetracycline on the bacillum Listeria monocytogenes

By: Alicia Agnew

Virginia-Maryland Regional College of Veterinary Medicine, Class of 2013

Listeria monocytogenes is a food-borne pathogen that causes disease in twenty-eight mammalian species including humans.  The bacterium is opportunistic, and for this reason, outbreaks tend to be sporadic in nature.  Listeria monocytogenes is ubiquitous in nature, so forty environmental samples were collected from a goat farm in Maryland.  Twenty samples were then isolated to purity using Oxford Enrichment media.  These samples were then tested for sensitivity to the antibiotics Penicillin Procaine G and Oxtetracycline.  I hypothesized that the combination of these two drugs would have a synergistic effect in inhibition of bacterial growth.  Microtitrator tests were carried out for each environmental sample as well as a sample obtained from a commercial lab.  The minimum inhibitory concentrations of Procaine G and Oxytetracycline were determined individually for each sample and then in combination for each sample to test for synergism.  The results of the study were inconclusive, showing neither an antagonistic nor a synergistic effect when the two drugs were used in combination.