| Summary: | Assam tea plants (<i>Camellia sinensis</i> var. <i>assamica</i>) or Miang are found in plantations and forests of Northern Thailand. Leaf fermentation has been performed for centuries, but little information is available about their associated microbial community. One hundred and fifty-seven bacterial isolates were isolated from 62 Assam tea leaf samples collected from 6 provinces of Northern Thailand and classified within the phyla of Firmicutes, Actinobacteria, and Proteobacteria. Phayao and Phrae provinces exhibited the highest and the lowest bacterial diversities, respectively. The bacterial community structural pattern demonstrated significant differences between the west and the east sides. Since some <i>Bacillus</i> spp. have been reported to be involved in fermented Miang, <i>Bacillus</i> spp. isolated in this study were chosen for further elucidation. <i>Bacillus siamensis</i> ML122-2 exhibited a growth inhibitory effect against <i>Staphylococcus aureus</i> ATCC 25923 and MRSA DMST 20625, and the highest survival ability in simulated gastric and intestinal fluids (32.3 and 99.7%, respectively), autoaggregation (93.2%), cell surface hydrophobicity (50.0%), and bacterial adherence with Vero cells (75.8% of the control <i>Lactiplantibacillus</i><i>plantarum</i> FM03-1). This <i>B. siamensis</i> ML122-2 is a promising probiotic to be used in the food industry and seems to have potential antibacterial properties relevant for the treatment of antibiotic-resistant infections.
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