Date Approved


Degree Type

Open Access Senior Honors Thesis

Department or School


First Advisor

Anne Casper, PhD

Second Advisor

Paul Price, PhD

Third Advisor

Aaron Liepman, PhD


The lack of new antibiotics capable of treating the ever-increasing number of antibiotic-resistant bacterial infections reflects the difficulty of finding new antimicrobial compounds. Most antibiotics were originally discovered from microorganisms that were grown in isolation. The interspecies interactions involved in co-culturing microbes, growing two or more strains together, can impact the types and increase production levels of antimicrobial compounds compared to monocultures. The purpose of this study was to determine whether co-culturing antibacterial producers would result in increased antibiotic production. Mixed student samples from the EMU Tiny Earth lab were utilized for this study because there was a higher chance that interspecies interactions were responsible for previously observed antibiotic activity. The samples were purified and antibiotic activity was verified by testing against safe relatives to the ESKAPE pathogens. Strain genera were determined with PCR and 16s rRNA gene sequencing. Co-cultures of previously mixed strains were plated on solid TYME media with and without physical contact and the zones of inhibition (ZOI) were measured; isolates with the highest levels of activity were then co-cultured in liquid EPSM to extract their secondary metabolites, including any potential antibiotics. Overall, there was no difference between size of ZOIs when co-cultures were physically separated versus when mixed together. Further, the majority of organic extracts from co-cultured strains had no difference in diameter of ZOIs. Organic extracts of strain EMU 941 had a large ZOI against S. aureus and seemed to induce production of antibiotics by strain EMU 942 when co-cultured. These results indicate co-culturing has the potential to induce antibiotic production, but more research is necessary to determine which strains act as inducers and producers.

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