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

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.