2016 Volume 32 Issue 1 Pages 13-24
To evaluate the usefulness of the lactic acid bacteria and staphylococci isolated from Thai fermented foods, we investigated their environmental adaptability and stress tolerance. Most of the strains isolated were tolerant to acidic conditions (pH 3.5 or 4.0). There were also some strains tolerant to high NaCl concentration (10％NaCl), high temperature (45℃), or alkalinity (pH 8.5 or 9.0). Tolerance to stress, acidity, and high temperature was found mainly among lactic acid bacteria strains, whereas tolerance to alkalis and high NaCl concentration occurred mainly in Staphylococcus strains. Comparison of strains isolated from Thai fermented foods and those isolated from Japanese fermented foods showed that the percentage of acid-resistant strains was significantly higher in Thai fermented foods, and that strains with both acid and high-temperature tolerance were isolated only from the Thai foods. Adaptability to a broad pH range was also greater in the strains isolated from Thai fermented foods. Resistance to alkaline conditions or high NaCl concentration was found mainly in Staphylococcus strains, isolated from either Thai or Japanese fermented foods. Our finding that all of the Staphylococcus species isolated showed either alkaline or high-NaCl-concentration tolerance, or both, indicated that Staphylococcus species with these tolerances were widely distributed in these fermented foods. Because the relationship between tolerance and source locality of the isolates was low, and the characteristics of the species isolated differed between Thailand and Japan, there appear to be differences in environmental adaptability and stress tolerance among the different constituent species. Strains that showed tolerance to acid or high temperature and were isolated from Thai fermented foods were assigned to a greater diversity of species than were the Japanese isolates. Furthermore, strains of the same species isolated from Thai fermented foods showed a variety of tolerances to environmental stress. These results reveal the distinctive nature of the strains isolated from Thai fermented foods; these strains are unique bioresources that should be suitable for various applications.
