Antibacterial activity of lactic acid bacteria isolated from southern Thailand traditional fermented foods
2000
Charernjiratrakul, W. (Prince of Songkla Univ., Songkhla (Thailand). Faculty of Sciences. Dept. of Microbiology)
Total of 212 isolates of lactic acid bacteria was isolated from 329 samples of southern Thailand traditional fermented food. They were identified as 198 isolates of Lactobacillus and 14 isolates of Pediococcus. When tested by agar spot method, 193 out of 212 isolates showed antibacterial activity against 4 indicator strains including Bacillus cereus ATCC 11778, Staphylococcus aureus ATCC25923, Escherichia coli ATCC25922, and Salmonella typhimurium 3230. However, only 10 isolates showed antibacterial activity against the indicator strains when tested with MRS agar containing 0.2 percent glucose or incubated under anaerobic condition to minimize the effect of organic acid or hydrogen peroxide, respectively. These 10 isolates were analyzed further under conditions excluding the effect of organic acid and hydrogen peroxide in broth medium. As indicated by turbidity, only and isolate of P5 inhibited growth of the indicator strains. None of these 10 isolates showed antibacterial activity when tested by agar well diffusion method. Among these 10 isolates, 6 isolates were identified as Lactobacillus plantarum and 2 isolates were identified as either L. brevis or L. fermentum. L. fermentum P5 was further characterized. It was found that this strain was able to grow well and produce antibacterial compounds in MRS and CJ media at 30-35 deg C. It exhibited the maximal growth rate and highest rate of antibacterial compound production at between 6 and 12 h, but both activities were stable after 24 h of incubation at 35 deg C in MRS broth. In addition to organic acid, L. plantarum P5 could produce a heat stable protein which inhibited growth of gram positive better than gram negative bacteria. Thus, it suggests that this protein may be a bacteriocin.
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