Interactions among lactic acid starter and probiotic
bacteria were investigated to establish adequate combinations
of strains to manufacture probiotic dairy products.
For this aim, a total of 48 strains of Streptococcus
thermophilus, Lactobacillus delbrueckii subsp. bulgaricus,
Lactococcus lactis, Lactobacillus acidophilus, Lactobacillus
casei, and Bifidobacterium spp. (eight of each)
were used. The detection of bacterial interactions was
carried out using the well-diffusion agar assay, and
the interactions found were further characterized by
growth kinetics. A variety of interactions was demonstrated.
Lb. delbrueckii subsp. bulgaricus was found
to be able to inhibit S. thermophilus strains. Among
probiotic cultures, Lb. acidophilus was the sole species
that was inhibited by the others (Lb. casei and Bifidobacterium).
In general, probiotic bacteria proved to be
more inhibitory towards lactic acid bacteria than vice
versa since the latter did not exert any effect on the
growth of the former, with some exceptions. The study
of interactions by growth kinetics allowed the setting
of four different kinds of behaviors between species of
lactic acid starter and probiotic bacteria (stimulation,
delay, complete inhibition of growth, and no effects
among them). The possible interactions among the
strains selected to manufacture a probiotic fermented
dairy product should be taken into account when choosing
the best combination/s to optimize their performance
in the process and their survival in the products
during cold storage