Date of Award


Degree Type


Degree Name

Master of Science (MS)



First Advisor

Dr. Eric Gilbert

Second Advisor

Dr. George Pierce

Third Advisor

Dr. Kuk Chin


Polymicrobial biofilms contain multiple microbial species encased in an extracellular polymeric matrix. Synergistic interactions within polymicrobial biofilms contribute to elevated antibiotic resistance and chronic infections; furthermore, prevention and treatment is still an unresolved issue. The yeast Candida albicans and the Gram positive bacterium Streptococcus mutans are biofilm-forming oral pathogens that interact mutualistically, and were investigated in this work. Crystal violet-based biofilm formation assays were used to measure the effect of extracts from Rhamnus prinoides (gesho), an East African plant used in traditional medicine, on biofilm formation. The biomass of dual species biofilms was 70% greater than single-species biofilms, indicating a synergistic interaction. Treatment with gesho extracts reduced both single-species and polymicrobial biofilm biomass by more than 90% relative to controls. Imaging by epifluorescence microscopy supported the findings of the biofilm formation assays. In conclusion, gesho exhibited significant potential for use as an anti-biofilm agent and warrants further investigation.