Background: Probiotics are increasingly used to treat infectious diarrhea and antibiotic-associated diarrhea. Many probiotic
bacteria are classified in general such as Lactobacillus and are able to colonize the gastrointestinal tracts of infants.
Objective: This study was performed to detect antimicrobial substances and activity in 200 Lactobacillus isolates obtained
from healthy Thai newborn feces.
Material and Method: Reuterin production was detected by the spot overlay technique and colorimetric assay. Antimicrobial
activity was tested by using a well diffusion, agar method.
Results: Lactobacillus strain MSMC64-1 produced reuterin and demonstrated potent antimicrobial activity against seven
pathogenic indicator strains with very strong inhibitory activities against Salmonella typhi DMST 5784 and methicillin resistant Staphylococcus aureus (MRSA) DMST 20651. There was strong inhibitory activity against methicillin resistant Staphylococcus aureus (MRSA) DMST 20654, Vibrio parahaemolyticus DMST 5665 and Shigella dysenteriae DMST 15111. There was moderate to weak inhibitory activities against Vibrio cholerae DMST 2873 and Helicobacter pylori (H40). The Lactobacillus strain MSMC 64-1 showed resistance to acidic pH (pH 2, 3, 4) and tolerance to 1%, 2%, 3%, and 4% bile concentrations. Sequencing of the 16S ribosomal DNA identified the candidate’s strain as Lactobacillus reuteri with 98% sequence homology.
Conclusion: The active isolate could potentially be used as a probiotic to prevent and treat enteric infections.

Keywords: Probiotics, Antimicrobials, Lactobacillus