Doctoral Dissertations

Date of Award


Degree Type


Degree Name

Doctor of Philosophy


Food Science and Technology

Major Professor

Federico M. Harte

Committee Members

C. Neal Stewart Jr., Philip M. Davidson, Svetlana Zivanovic


Ilex paraguariensis, is used in the preparation of a widely popular tea beverage (Yerba Mate) mainly produced and consumed in the countries of Uruguay, Paraguay, Argentina and Brazil. Dialyzed aqueous extracts were screened for antimicrobial activity against Escherichia coli O157:H7, Staphylococcus aureus, methicillin-resistant S. aureus and S. pseudintermedius, and Pseudomonas syringae pv. tomato.

Using a concentrated extract, S. aureus was found to be the more sensitive to extracts than E. coli O157:H7. Minimum inhibitory concentration (MIC) was defined as the lowest concentration of extract tested that did not allow bacterial growth (inhibition) above the original inoculums of approximately 5.0-6.0 log CFU/ml after 24 hr. The minimum bactericidal concentration (MBC) was defined as the lowest concentration tested where bacterial death (inactivation) was observed after 24 hr. MBCs were determined to be ca. 0.150- 0.800 mg protein equivalent/ml and 0.025-0.050 mg protein equivalent/ml against E. coli O157:H7 and S. aureus respectively.

Using a lyophilized extract, MICs were determined to be 5 mg/ml for two strains of E. coli O157:H7 and MBCs 5 mg/ml for E. coli O157:H7 strain ATCC 43894 and 10 mg/ml for E. coli O157:H7 strain ‘Cider’ in microbiological media. An approximately >4.5 log reduction was observed for E. coli O157:H7 treated with 40 mg/ml extract in modified apple juice, which approximate to the requirements of the United States Code of Federal Regulations (21 CFR part 120).

We demonstrated antimicrobial effectiveness of aqueous extracts after 24 hr at 1 and 2 mg/ml against all strains of methicillin-resistant S. pseudintermedius and of S. aureus tested respectively. An approximately >5 log reduction was observed in all strains at all concentrations after 24 hr. Methicllin-resistant Staphylococcus aureus (MRSA) strains appeared more susceptible to the extract than methicillin-resistant Staphylococcus pseudintermedius (MSRP) strains.

It was concluded that aqueous extracts of Yerba Mate demonstrated broad activity against foodborne, human, animal and plant pathogenic bacteria, including strains demonstrating resistance to certain antibiotics.

Files over 3MB may be slow to open. For best results, right-click and select "save as..."