Antibacterial, antidermatophytic and antitoxigenic activities of onion (Allium cepa L.) oil.

The inhibitory effect of onion oil against the growth of various isolates of bacteria representing Gram-positive (4 isolates) and Gram-negative (4 isolates) species were studied. Results show that onion oil was highly active against all Gram-positive bacteria tested and only one isolate (Klebsiella pneumoniae) of Gram-negative bacteria. The inhibitory effect of onion oil against nine different species of dermatophytic fungi were also studied. Onion oil (200 ppm) completely inhibited the growth of Microsporum canis, M. gypseum and Trichophyton simii while the growth of both, Chrysosporium queenslandicum and Trichophyton mentagrophytes was completely inhibited by 500 ppm of onion oil. The growth of four other species of dermatophytic fungi was gradually reduced by increasing the concentrations of onion oil. The inhibitory effect of onion oil was also tested against four toxigenic isolates of fungi. Onion oil at different concentrations (100, 200 and 500 ppm) tested gradually reduced fungal growth and aflatoxin production by Aspergillus flavus IMI 89,717 and A. parasiticus var. globosus IMI 120,920. Fungal growth and production of sterigmatocystin and rubratoxin A by A. versicolor IMI 16,139 and Penicillium rubrum IMI 136,127 were completely inhibited by the addition of 200 ppm onion oil.