Antibacterial and antioxidant activities of acid and bile resistant strains of lactobacillus fermentum isolated from Miang

Miang is a kind of traditional fermented tea leaves, widely consumed in northern Thailand as a snack. It contains several kinds of Lactobacilli spp. The aim of this study was to isolate strains of Lactobacillus fermentum from miang and to investigate their antibacterial and antioxidant activities. The agar spot and well assays were used for determination of antibacterial power. The antibacterial mechanism was investigated by cell morphologic change under scanning electron microscope (SEM). Antioxidant activity was studied by means of free radical scavenging and ferric reducing power assays. The acid and bile screening tests indicated that L. fermentum FTL2311 and L. fermentum FTL10BR presented antibacterial activity against several pathogenic bacteria: Listeria monocytogenes DMST 17303, Salmonella Typhi DMST 5784, Shigella sonnei DMST 561 (ATCC 11060)and Staphylococcus aureus subsp. aureus DMST 6512 (ATCC 6538Ptm). The results from SEM suggested that the antibacterial action was due to the destruction of cell membrane which consequently caused the pathogenic cell shrinking or cracking. The antioxidant study suggested that both L. fermentum FTL2311 and L. fermentum FTL10BR strains could liberate certain substances that possessed antioxidant activity expressed as trolox equivalent antioxidant capacity (TEAC) and equivalent concentration (EC) values for free radical scavenging and reducing mechanisms, respectively. The supernatant of L. fermentum FTL2311 broth revealed TEAC and EC values of 22.54±0.12 and 20.63±0.17 µM.mg-1 respectively, whereas that of L. fermentum FTL10BR yielded TEAC and EC values of 24.09±0.12 and 21.26±0.17 µM.mg-1 respectively. These two strains isolated from miang present high potential as promising health-promoting probiotics.

Vitamin B12 synthesis by bacillus in miang.

It has been shown that vitamin B12 in fermented food is synthesized by a wide range of bacteria. Miang is a native food product made from whole leaves which is commonly consumed mainly in the Northern part of Thailand. Studies on 48 sample of Miang showed that they contained relatively high vitamin B12 content, ranged from 3.9 to 30.1 ng/g. Miang Som contained the highest vitamin B12 while Miang Van had the lowest vitamin B12 content. Three species of bacteria, i.e., Bacillus subtilis, B. megaterium and B. sphaericus were isolated from 5 samples of Miang. Re-inoculation of these species of bacteria into the broth, medium for vitamin B12 production and soybean showed that B. subtilis could not produce vitamin B12 in these media. Only B. megaterium and B.sphaericus synthesized vitamin B12. This is the first report to show that B.sphaericus has such ability.