The effectiveness of processed grapefruit-seed extract as an antibacterial agent: I. An in vitro agar assay

J Altern Complement Med. 2002 Jun;8(3):325-32. doi: 10.1089/10755530260128014.


Objectives: Grapefruit-seed extract (GSE) Citricidal has, in recent reports, been reported to be successful in combating a variety of common infectious agents. In our study, drops of concentrated grapefruit-seed extract were tested for antibacterial properties against a number of gram-positive and gram-negative organisms.

Design: Sixty-seven (67) distinct biotypes were tested for their susceptibilities to the GSE as well as to 5 other topical antibacterials (Silvadene, Sulfamylon, Bactroban, Nitrofurazone, and Silvadene, Nystatin). Wells were punched into Mueller-Hinton agar plates, which were then inoculated with the organism to be tested; each well was then inoculated with one of the antibacterial agents. After an overnight incubation period, the plates were checked for zones of bacterial susceptibility around the individual wells, with a measured susceptibility zone diameter of 10 mm or more considered a positive result.

Results: The GSE was consistently antibacterial against all of the biotypes tested, with susceptibility zone diameters equal to or greater than 15 mm in each case.

Conclusions: Our preliminary data thus suggest an antibacterial characteristic to GSE that is comparable to that of proven topical antibacterials. Although the GSE appeared to have a somewhat greater inhibitory effect on gram-positive organisms than on gram-negative organisms, its comparative effectiveness against a wide range of bacterial biotypes is significant.

MeSH terms

  • Anti-Bacterial Agents / pharmacology*
  • Citrus*
  • Gram-Negative Bacteria / drug effects*
  • Gram-Positive Bacteria / drug effects*
  • Humans
  • In Vitro Techniques
  • Microbial Sensitivity Tests
  • Plant Extracts / pharmacology
  • Seeds*


  • Anti-Bacterial Agents
  • Plant Extracts