เอกสารการประชุมวิชาการและเสนอผลงานวิจัย มหาวิทยาลัยทักษิณ ครั้งที่ 19 2552 - page 790

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2
Abstract
The antimicrobial activity of 5 Thai herbs [Acanthus ebracteatus Wall., Glycyrrhiza glabra (Linn. ),
Zingiber zerumbet (L.) Smith, Andrographis paniculata Wall.ex Nees and Centella asiatica (Linn.) Urban]
extracts using water, 35% ethanol and boil down water were evaluated against indicator microorganisms
(Staphylococcus aureus TISTR 517, Escherichia coli TISTR 887, Bacillus subtilis ATCC 6633, and Candida
albicans TISTR 5779) by means of broth microdilution method. The Minimal Inhibitory Concentration (MICs)
and Minimum Batericidal Concentration (MBCs) or Minimum Fungicidal Concentration (MFCs) values of the
extracts were compared with three antimicrobial drugs (Amphotericin B, Kanamycin and Gentamicin). MBCs or
MFCs were determined by spread plate technique when less than 5 colonies were formed. Moreover, the effects
of temperature and pH on the antimicrobial activity of herb extracts were elucidated. The results indicated that
water extracts of the most of herbs had no antimicrobial activity against all tested indicator microorganisms,
exceptionally, S. aureus and B. subtilis were susceptible to water extracts of Glycyrrhiza glabra (Linn.), gave
MIC as 2.36 mg/ml and B. subtilis was susceptible to water extracts of Andrographis paniculata (MIC = 9.42
mg/ml.). 35% ethanol extracts of Glycyrrhiza glabra (Linn. ) had adverse effects on S. aureus and B. subtilis
showing MICs at 0.08 and 0.04 mg/ml, respectively. Boil down water extracts of all tested herbs inhibited the
growth of any tested microorganisms. MICs from boil down water extracts of Glycyrrhiza glabra (Linn.) against
S. aureus and B. subtilis were 0.59 mg/ml. The extracts of all tested herbs had lower antimicrobial activity than
that antimicrobial drugs. Moreover, the temperature and pHs had no effect on antimicrobial activity of, the most,
Thai herb’s extracts. Interestingly, the anti-B. subtilis activity of water extracts of Glycyrrhiza glabra (Linn.) and
boil down water extract of Acanthus ebracteatus Wall. was increased after treated at 121 ºC., gave MIC decreased
to 1.18 mg/ml. activity. Overall, it could assume that Glycyrrhiza glabra (Linn.) had the broadest spectrum of the
antimicrobial activity but still had lower activity in comparision with antimicrobial drugs. B. subtilis was proved
to be the most sensitive microorganism. The temperature and pH had no effect on antimicrobial activity of, the
most, the herb extracts.
Keywords: Minimum inhibitory concentration, Antimicrobial activity, Thai herbs, Extracts
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