Common Garlic (Allium sativum L.) has Potent Anti-Bacillus anthracis Activity
Ethnopharmacological Relevance: A number of common plants found in the Indian subcontinent, e.g., Aegle marmelos (L.) Correa (Bael), Allium cepa L. (Onion), Allium sativum L. (Garlic), Azadirachta indica A. Juss. (Neem), Berberis asiatica Roxb. ex DC. (Daruharidra), Coriandrum sativum L. (Coriander) Curcuma longa L. (Turmeric), Mangifera indica L. (Mango), Morus indica L. (Black mulberry, Shetuta), Ocimum tenuiflorum L. (Ocimum sanctum L., Holy Basil, Tulsi), Ocimum gratissimum L. (Ram Tulsi), Zingiber officinale Roscoe (Ginger), are indicated to have antimicrobial activity and given in diarrhea, dysentery stomachache or as stomachic based upon traditional knowledge and usage profile as per the available literature. They are also given to livestock for their supposed health benefit. Most of the time, they are used for the treatment of different illnesses in spite of the absence of any definitive pieces of evidence for their supposed activity, knowledge about the active principles or their mode of action in pathogens. Anthrax, a disease caused by Bacillus anthracis, remains an important but relatively neglected endemic disease of animals and humans in remote areas of the Indian subcontinent. People in poor endemic areas usually rely on symptom based treatment utilizing parts of different common medicinal plants. Azadirachta indica A. Juss. (Neem) and Curcuma longa L. (Turmeric) have been indicated in literature for anthrax disease based upon traditional use while other plants evaluated in the current study have been indicated for different gastrointestinal conditions. Aim of the Study: Evaluate commonly available edible plants used in the traditional medicine to treat gastrointestinal diseases including those indicated especially for anthrax for potent anti-Bacillus anthracis activity in a form amenable to use in the endemic areas. Materials and Methods: Aqueous extracts made from different plant parts were screened for their anti-Bacillus anthracis activity. The bacteriostatic and bactericidal activities of the extracts were assessed using Agar-well diffusion assays and liquid broth cultures. The bioactive fractions from the most potent anti-Bacillus anthracis activity displaying Aqueous Garlic Extract (AGE) were isolated by TLC coupled bioautography followed by their characterization using GC-MS. The AGE was assessed for its thermostability and any potential antagonistic interaction with the FDA-approved antibiotics used for anthrax control. Results: Garlic (Allium sativum L.) was identified as the most promising candidate with bactericidal activity against Bacillus anthracis. It consistently inhibited the growth of Bacillus anthracis in agar-well diffusion assay and decreased the viable colony forming units counts in liquid-broth cultures by 6-logs within 6-12 h. GC-MS analysis of the TLC separated bioactive fractions of AGE indicated the presence of previously unreported constituents such as phthalic acid derivatives, acid esters, phenyl group-containing compounds, steroids etc. The AGE displayed acceptable thermostability (>80% anti-Bacillus anthracis activity retained on incubation at 50oC for 12 h) and did not antagonize the activity of FDA-approved antibiotics used for anthrax control. Conclusion: The Aqueous Garlic Extract (AGE) has potent anti-Bacillus anthracis activity better than Azadirachta indica A. Juss. (Neem) and Mangifera indica L. while Curcuma longa L. (Turmeric) does not have any activity in the assays performed. Further work should be undertaken to explore the possible application/use of AGE in preventing anthrax incidences in endemic areas.