The nature of antimicrobial substances was also investigated and shown to be dependent on
the production of organic acids, in particular the lactic acid. Time-kill assay showed that the viability
of the S. sonnei was decreased by 2.7–3.6 log CFU/ml after contact with CFCS (cell-free culture supernatants)
of four lactobacilli for 2 h, which confirmed the result of the agar-well assay.