The inhibitory effect of lactobacilli on the growth of different pathogens was studied. The degree of inhibition was measured by disc assay in different media, showing that the inhibitory substance(s) can be extracellular and diffusible. The associative cultures were performed with lactobacilli and Escherichia coli in a relationship of 1:1 or 103:1. In the first experiments, the E. coli inhibition began at 9 h after culturing. In the experiments with lower levels of different intestinal pathogens, associative cultures were incubated for 4–6 h obtaining different degrees of inhibition with the highest being for E. coli and Klebsiella pneumoniae. After a day of incubation, we did not recover viable pathogens from the mixed cultures, while lactobacilli grew to 108–109 microorganisms per ml. The inhibition of pathogens was not due to pH alone, because the addition of different organic acids to culture media did not inhibit their normal growth. Lactobacillus casei and Lactobacillus acidophilus in this study can be considered a potential biotherapeutic treatment in patients infected with certain intestinal pathogens.

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