2.2. Isolation and preservation
Ten milliliters of samples were homogenized in 90 mL 1 g/
100 mL peptone water. Dilutions up to 108 were prepared and
1 mL aliquots from 105, 106, and 107 dilutions were spread onto
agar plates containing M17 selective medium (pH 6.8) (Terzaghi &
Sandine, 1975). The plates were incubated at 42 C for 3 days under
microaerophilic conditions. The plates with colony forming
units (CFU) of 30e300 were used for S. thermophilus isolation.
Isolated bacteria were enriched in M17 broths, purified using the
streak plate technique, and further stored in 20 mL/100 mL
glycerol-M17 medium at 80 C.