University of Minnesota
MICaB Graduate Program
MICaB Home | U of M Medical School | Graduate School

Unit's home page.

Current Students

Shannon Kordus

Thesis Advisor: Anthony Baughn

Year entered: 2013

Degrees received:
B.S., University of Wisconsin, LaCrosse, WI, 2010
M.S., Boston University ,Boston, MA, 2013

Honors and awards:

  • Council of Graduate Student (COGS) Grant Award, May 2017
  • Sigma Xi Poster Award, May 2017
  • ASM Conference on Antibacterial Development Student Travel Award, November 2016
  • MICaB Travel Award Recipient, Fall 2016
  • MICaB Student Service Award 2016
  • MICaB Student Rep 2016-2017
  • 3 Minute Thesis People’s Choice Award 2016
  • Young Scientist Travel Award 2016
  • Mycobacteria Research Lab’s Outstanding Poster 2016

Co-infections with HIV and tuberculosis (TB) have claimed millions of lives in recent years. In addition to TB, secondary-infections are an important cause of death in HIV-infected individuals. As such, these individuals receive lifetime trimethoprim (TMP)-sulfamethoxazole (SMX) prophylaxis to protect against opportunistic infections. Interactions between SMX and other antimicrobials, such as the highly selective TB drug para-aminosalicylate (PAS), have not been studied. SMX inhibits microbial folate biosynthesis and can be antagonized by the folate precursor para-aminobenzoate (PABA). Although no direct evidence has been published to date, it was previously proposed that PAS can be converted to a hydroxylated form of dihydrofolate (DHF), hydroxy-DHF which likely inhibits the M. tuberculosis DHF reductase (DHFRMtb). To test this hypothesis and shed light on the selectivity of PAS for M. tuberculosis, we performed enzymatic assays using purified recombinant DHFRMtb and Escherichia coli DHF-reductase(DHFREc) and analytically pure hydroxy-DHF. We found that hydroxy-DHF inhibits DHFRMtb. In contrast, we demonstrate that hydroxy-DHF does not inhibit purified DHFREc and is a competent substrate for this enzyme.Upon further analysis of the active sites of these enzymes, we found DHFREc has a much larger and more hydrophobic active site compared to DHFRMtb, which we hypothesize is responsible for PAS selectivity. Strikingly, we find that growth of an E. coli PABA auxotrophic strain can be restored by supplementation with PAS, indicating that PAS can serve as a functional analog of PABA in E. coli folate metabolism. To extend this analysis, we determined whether PAS could antagonize the effects of SMX in E. coli and several other bacterial species. In all organisms tested, except for M. tuberculosis, PAS antagonized SMX activity. Conversely, in M. tuberculosis SMX antagonized PAS activity. Our findings, for the first time, confirm the biochemical mode of action and molecular basis for species selectivity of PAS. More importantly, these findings highlight the critical need to evaluate the danger of co-administration of TMP-SMX and PAS in HIV-TB co-infected individuals.


  • Minato, Y., Thiede, J., Kordus, S.L., McKlveen, E., Turman, B.J., and Baughn A. 2015. Mycobacterium tuberculosis folate metabolism and the mechanistic basis for para-aminosalicylic acid susceptibility and resistance. Antimicrobial Agents and Chemotherapy. 59:5097-106.
  • Thiede, J.M., S. L. Kordus, B. J. Turman, J. A. Buonomo ,C. C. Aldrich, Y. Minato and A. D. Baughn. 2016. Targeting intracellular p-aminobenzoic acid production potentiates the anti-tubercular action of antifolates. Scientific Reports. 6:38083. doi: 10.1038/srep38083.