Antimicrobial Synergy between Aminoglycosides and Licorice Extract in Listeria monocytogenes

Myungseo Park, Liz Horn, Victoria Lappi, Dave Boxrud, Craig Hedberg, Byeonghwa Jeon

Research output: Contribution to journalArticlepeer-review

2 Scopus citations


Listeria monocytogenes is a foodborne pathogen that can develop serious invasive infections. Among foodborne pathogens, L. monocytogenes exhibits the highest case fatality despite antibiotic treatment, suggesting the current therapy should be improved. Although ampicillin and gentamicin are used as a combination therapy to treat listeriosis, our results showed there is no synergy between the two antibiotics. We discovered that aqueous extract of licorice generated significant antimicrobial synergy when combined with aminoglycosides, such as gentamicin, in L. monocytogenes. In the presence of 1 mg/mL licorice extract, for instance, the minimum inhibitory concentration (MIC) of gentamicin was reduced by 32-fold. Moreover, antimicrobial synergy with licorice extract made gentamicin-resistant clinical isolates of L. monocytogenes susceptible to gentamicin. Given the common use of licorice as a food sweetener in Western countries and a herb in Oriental medicine, our findings suggest that licorice extract can be potentially used as an antibiotic adjuvant to improve the efficacy of antimicrobial treatment of listeriosis.

Original languageEnglish (US)
Article number440
Issue number4
StatePublished - Apr 2022

Bibliographical note

Funding Information:
Funding: This study was supported by a research grant (20SFR-2YR150BJ) from the Healthy Foods, Healthy Lives Institute.

Publisher Copyright:
© 2022 by the authors. Licensee MDPI, Basel, Switzerland.


  • Listeria
  • aminoglycosides
  • antimicrobial synergy
  • drug potentiation
  • plant extract

PubMed: MeSH publication types

  • Journal Article


Dive into the research topics of 'Antimicrobial Synergy between Aminoglycosides and Licorice Extract in Listeria monocytogenes'. Together they form a unique fingerprint.

Cite this