2.6. Detection of bacterial interactions (well-diffusion agar assay)
Interactions among lactic acid strains were investigated. Ten milliliters
of MRS (lactobacilli) or LAPTg agar (streptococci) were melted, kept
at 45 °C, and vigorously mixed with 70 μl of an overnight culture of
lactobacilli (L. bulgaricus CRL871 or Lactobacillus amylovorus CRL887) or
streptococci (S. thermophilus CRL803 and CRL415), and poured into
Petri dishes. Wells of 5 mm in diameter were made in the agar layer,
and 30 μl of the cell-free supernatant of each strain was placed into
each well. After 24 h of incubation at 37 °C, the plates were examined
for zones of inhibition which would be an indication that these produce
antibacterial substances.