Document Type

Open Access Thesis

Embargo Period


Degree Program

Food Science

Degree Type

Master of Science (M.S.)

Year Degree Awarded


Month Degree Awarded



The use of antibiotics in animal feed is a large cause of concern due to bacterial resistance, which occurs when bacteria change after exposure to antibiotics and become less affected by the drug. Consequently, the desire to find a replacement for these antibiotics has garnered interest in both farmers and consumers. The ideal substance would display antimicrobial activity without promoting bacterial resistance and would still function as a growth promoter in animals. One antimicrobial that fits this criterion is carvacrol, a compound found in oregano extract. Carvacrol exhibits antimicrobial activity in a number of bacteria, including E.coli O157:H7 and S. enteritidis. In this study, the effectiveness of carvacrol nanoemulsions against E.coli and S. enteritidis growth in a micro-broth dilution assay was tested, as well as the use of alamarBlueTM dye reagent as a bacterial viability indicator. The carvacrol nanoemulsion was diluted in TSB to obtain 2000, 1000, 500, 250, 125, and 62.5 ppm, then aliquots of 100 μl of each dilution were added to a 96-well microtiter plate. Test group wells were inoculated with 100 μl of microorganism while control cells remained uninoculated, and the plate was incubated for 24h at 37 °C. After incubation, 10μl of alamarBlueTM was added to each well, and the microtiter plate was incubated for one hour. After one hour, the color changes were analyzed both visually and via fluorescence. Additionally, a traditional plating assay in which samples were plated on tryptic soy agar was done alongside the microtiter plate assay. It was found that the minimum inhibitory concentration of carvacrol needed to inhibit E. coli growth was 500ppm, and to inhibit S. enteritidis growth was 800ppm. These results show that carvacrol may be suitable as a possible replacement for antibiotic in animal feed in the future.

First Advisor

Lynne McLandsborough