Two hundred succinic acid-producing bacteria were isolated from cattle dung, soil, bovine rumen, and tree bark collected in Thailand. Eighty-four isolates exhibited a clear zone on the screening plate. The production was analyzed qualitatively by the TLC method and quantitatively by the HPLC method. The succinic acid was in the range of 0.003-0.97 g/g glucose. Only 28 isolates were selected based on morphology, cultural and phenotypic characteristics. The isolates were divided into three groups. Twenty-three isolates in Group I were identified as Enterococcus, 2 isolates in Group II were identified as Lactobacillus, and 3 isolates in Group III were identified as Clostridium. Enterococcus durans (isolate NS15-dA1) and Enterococcus hirae (isolate NS15-bA2) were selected for further study for succinic acid production. The optimum conditions were 60 g/L of glucose, 30 g/L of yeast extract (NS15-dA1), and 30 g/L of tryptone (NS15-bA2) at pH 7.0 and 37 °C. The highest amounts of succinic acid were obtained from the isolates NS15-dA1 (51.69±0.17 g/L) and NS15-bA2 (53.05±0.35 g/L)
