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Isolation and Identification of Lactic Acid Bacteria from Traditional Fermented Fish and Pork Foods of Laos
Thesis Abstract:
The objectives of the research were to (1) isolate lactic acid bacteria from traditionally fermented fish and pork food products, namely: Pa dek, Pa dek kheuang, Pa chao, Sompa, Pa noi/Pa chom, Som khai pa, and Sommou; (2) screen the isolates for their ability to produce antibacterial substances; and (3) identify them to genera and species.
Selective media, GYP-CaCO3 were used for growing lactic acid bacteria at 30°C for 1-2 days, while spread plate and streak plate techniques were used for the isolation of lactic acid bacteria. The bacteria, which grew to colony surrounded with a zone of clearing, were considered as lactic acid bacteria and then purified for further study. For antibacterial activity test, agar diffusion methods were used; the cultures were grown in TGE broth for 24 hours at 30°C, the test was carried out on TGE agar by stabbing cultures into agar plate seeded with indicator bacteria in full transferring loop. Each plate may contain spots of 5-6 cultures. The agar plates were previously inoculated with indicator bacteria, Enterococcus faecalis and Samonella choleraceus subsp. cholaraceus by pure plate method. The cultures of LAB, which grew to colony with zone of clearing, were considered as antibacterial activity possessing. Phenotypic and biochemical methods were used for identification of selected LAB isolates. Colony appearance, cell form, shape, size, arrangement, motility, Gram stain, ability to ferment carbohydrates, DAP of cell wall, and lactic isomer produced were considered in the analysis.
With the means of approaches and methods used as mentioned above, 61 LAB were isolated—45 bacilli and 16 Cocci in shape. Out of these, 23 isolates had antibacterial activity. The 23 lactic acid bacteria could ferment 21 carbohydrates unevenly; thus, from their physiological and biochemical characteristics, they could be differentiated and grouped as follows:
• Into Genus Lactobacillus: 12 isolates, from Sompa-1 C-25, C-38, C-121; Pachao D-11, D-62, D-81; Panoi E-1 and Sommu I-1, I-6, I-9, I-10, I-11 were strains of Lactobacillus plantarum; one isolate I-7 from Sommou was L. pentosus; one isolate C-101 from Sompa 1 was L. fermentans and one isolate from C-40 from Sompa 1 was L. curvatus.
• Into Genus Pediococcus: D-23 from Pachao was Pediococcus halophilus; E-0, E-1 from Pachom and F-1, F-2 from Sompa 2 were P. pentosaceus.
• Into Genus Leuconostoc: I-5 from Sommou was Leuconostoc mesenteroides.
• Into Genus Enterococcus: D-14 from Pachao was Enterococcus avium and one isolate I-12 could not be identified. The 23 isolates were maintained in sterile 20 percent glycerol-distilled water solution at -80°C for further supply in a continuation of the research or in studies for their application.