Characterization of the Antibacterial Activity and Probiotic Properties of Lactic Acid Bacteria Isolated from Raw Fish and Nham-Plaa

Isolates of lactic acid bacteria from fish fillets and nham-plaa were screened to select the most suitable strains for the formulation of starter cultures with probiotic properties. Using an agar spot test, 30 of the 180 isolates that were tested inhibited at least one of four indicator strains; Staphylococcus aureus TISTR 118, Pediococcus acidilactici TISTR 051, Lactobacillus bulgaricus TISTR 415 and Listeria monocytogenes DMST 11256. Two bacterial isolates,13IS3 and 13IS4, from fish fillets were resistant to a low pH in lactic acid (pH 2.9-3.2) and in HCl (pH 2.2) and a high concentration of NaCl (6.0%) and bile salts (5.25%). These isolates were identified by morphological, biochemical and molecular analysis as Lactococcus lactis 13IS3 and Lactobacillus sakei 13IS4. The fermentation of nham-plaa model broth (NMB) by L. lactis 13IS3 seemed to be stimulated by 1.0% garlic extract and 0-1.5% NaCl at all temperatures of incubation. L. sakei 13IS4 fermented at a slower rate than L. lactis 13IS3, but fermented more rapidly in a 3.0%-garlic extract NMB with 0-1.5% NaCl at 30°C and in the same medium containing 1.0-1.5% NaCl at 35°C.