Background: Post-weaning bacterial infections in piglets caused by resistant strains have increased dramatically. Thai medicinal plants such as Piper retrofractum, Piper leptostachyum, Piper sarmentosum, Zingiber officinale, Plumbago indica, Piper betle, Caesalpinia sappan, Garcinia mangostana etc have been widely used in Thai traditional medicine to treat diarrhea. Thus, these plants were investigated antimicrobial activity against gram negative strain isolated from piglets with diarrhea.
Objective: To investigate antimicrobial activity of Thai medicinal plants and their isolated compounds in order to develop an alternative treatment against bacteria causing post-weaning diarrhea in piglets.
Material and Method: Antimicrobial activity of some Thai medicinal plants and their compounds were tested using disc
diffusion and broth dilution methods against bacteria associated with diarrheal disease including Escherichia coli and Salmonella spp. The extraction was performed by maceration in 95% ethanol.
Results: The results showed that all tested strains were sensitive to P. betle extract. As well as Plumbagin compound from Plumbago indica also showed antimicrobial activity against all microbes the same of P. betle extract with MIC between 5 to 10 mg/ml, which are different from the group of antibiotics with MIC values between 0.19-2.5 mg/ml, P. betle extracts inhibited Escherichia coli and Salmonella spp while some antibiotics can inhibit only some types.
Conclusion: The results support the use of Thai medicinal plants for treatment of diarrhea caused by these bacteria. This study also provides basic knowledge on antimicrobial activity against diarrheal microbe isolated from piglets. These results lead to further development of an effective formula of Thai medicinal plants for diarrheal disease in post-weaned piglets and other infectious diseases in the future.

Keywords: Antibacterial activity, Thai medicinal plants, Post-weaning diarrhea