Antimicrobial of some spices and medicinal plants on Shigella spp.

Avipha Ngamusa, Bunyut Suksringam


The antimicrobial activity of 16 spices and medicinal plants against Shigella spp. was
determined. Spices or medicinal plants, at the concentration 1% (wt/vol), was incorporated into
Mueller-Hinton(MH) agar. The Shigella tester strains were S. dysenteriae type 2 49/03, S. flexneri
type 2a DMST 17559, S. flexneri type 3a DMST 17560, S. boydii type 12 53/03, S. sonnei phase I
110/03, and S. sonnei phase II DMST 17561. It was found that clove, pepper, hairy basil, sweet
basil, holy basil, and kitchen mint demonstrated the inhibitory effect on Shigella spp. According to
agar dilution method, the minimum inhibition concentrations (MICs) of these plants ranged from
0.25-1% depending on the plant species as well as Shigella strains. Clove and pepper, which showed
the highest antibacterial potency, were selected for further investigation. It was established that when
clove or pepper (1% wt/vol) was added into MH agar, which was adjusted to various pH values (3.0,
3.5, 4.0, 4.5 and 5.0) and containing NaCl at various concentration (0, 1, 2, 3 and 4%) , significant
inhibition of Shigella spp. in all growth conditions was observed. However, the growth of Shigella
spp. in the control experiment was demonstrated on the medium containing NaCl at the
concentrations 0, 1 and 2% with the pH 5.5 and 4.5. The results of an orientation study involving the
addition of clove or pepper into salad cream, which inoculated with Shigella spp., and subsequently
stored at 4°C as well as 25°C, indicated no significant adverse affect on the survival of bacteria.
Rapid reduction in numbers of the Shigella spp. was illucidated, and no evidence of this bacterium
was found in both the treatments and control after 1 day of incubation.

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