In the present study, growth inhibitory effect of garlic, shallot and onion extract against wide range
of bacteria and fungi was observed. The antimicrobial activity of garlic, shallot and onion extracts
has been reported earlier. Ascalin is a new anti-fungal peptide, which has been isolated by Wang
and Ng from shallot bulbs 17. Yin and Tsao have reported that antifungal activity of seven Allium
plants including shallot, decrease when the extracts are subjected to increasing temperature. The
significant observation of the present study was heat stability of shallot extract at 121 °C and
retention of antimicrobial activity after drying. However, garlic and onion were sensitive to these
treatments. It is expected that antimicrobial compound of shallot was different from active
compounds of onion and garlic. However, fresh extract of garlic was more active than fresh ex
tract of shallot and onion. MIC values of shallot extract for bacteria and fungi indicated that fungi
were more sensitive than bacteria. No obvious differences between the sensitivity of Gram-
negative and Gram-positive bacteria, yeasts and filamentous fungi, were observed. The only
exception was Pseudomonas aeruginosa that tolerated 20 mg ml concentration of shallot extract.
This finding was contradictory to that of Ashrafief, in which Pseudomonas aeruginosa was sensitive
to aqueous shallot extract. According to physico-chemical analysis (data not shown) the
antimicrobial compound is likely to be a flavonoid with C14H18O6 formula. However, this needs
confirmation. Based on these results, we speculate, better potential for shallot extract in food
preservation at high temperature as well as in the therapy of dermatomycoses.