Characteristics of lactic acid bacteria isolated from kefir made of goat milk

Two strains of pure lactic acid bacteria capable of forming both acid and slime were isolated from the kefir made of goat milk. The isolated strains observed by morphological and physiological properties, and their 16S rDNA partial sequence were identified as Streptococcus salivarius subsp. thermophilus (LFG-1) and Lactococcus lactis subsp. lactis (LFG-2) with over 99% homology. The optimum temperature of Str. salivarius subsp. thermophilus LFG-1 for growth was 40-45 degrees C, and its generation time was 40.6 minutes. The final pH of cultured broth by Str salivarius subsp. thermophilus LFG-1 and the commercial strain Str thermophilus Body-1 for 24 hr at 37 degrees C were 4.30 and 4.55, respectively. The coagulative activity of Str salivarius subsp. thermophilus LFG-1 was almost as strong as that of commercial strain Str thermophilus Body-1. However, the LFG-2 strain showed lower coagulative activity than Str. thermophilus Body-1. The survival rate of lactic acid bacteria were between 22-29% in 0.3% bile extract. At pH 1.0 all of the bacteria were killed, and most of lactic acid bacteria died against pH 3.0. However, all lactic acid bacteria survived well at pH 4.5.