Antimicrobial and immunomodulatory potential of various Lactobacillus reuteri strains is closely connected to their metabolite production profile under given cultivation conditions. We determined the in vitro production of antimicrobial substances such as organic acids, ethanol, and reuterin by four strains of L. reuteri (L. reuteri E, L. reuteri KO5, L. reuteri CCM 3625, and L. reuteri ATCC 55730). All studied L. reuteri strains showed the ability to produce lactic acid, acetic acid, and ethanol with concominant consumption of glucose and together with phenyllactic acid-a potent antifungal compound-with concominant consumption of phenylalanine. The reuterin production from glycerol was confirmed for all analyzed lactobacilli strains except L. reuteri CCM 3625. Production of organic acids, ethanol, and reuterin is significantly involved in antimicrobial activity of lactobacilli which was determined using the dual-culture overlay diffusion method against six indicator bacteria and five indicator moulds. In comparison to the referential L. reuteri ATCC 55730, the highest inhibition potential was observed against Escherichia coli CCM 3988 and Pseudomonas aeruginosa CCM 3955. Among analyzed indicators of moulds, the growth of Alternaria alternata CCM F-128 was the most inhibited by all four analyzed L. reuteri strains. Finally, the immunomodulatory potential of analyzed lactobacilli were proven by the determination of the in vitro production of biogenic amines histamine and tyramine. L. reuteri CCM 3625 was able to produce tyramine, and L. reuteri E and L. reuteri KO5 were able to produce histamine under given cultivation conditions.

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We analysed and compared the ability of four strains of Lactobacillus reuteri of sheep origin ranked as NSLAB (non-starter lactic acid bacteria) to grow and produce biogenic amines (BA) under cultivation conditions varying in cultivation media and salt content. The production of biogenic amines was primarily dependent on the growth rate of L. reuteri under particular cultivation conditions. From among produced BA, tyramine appeared as the dominant one while L. reuteri CCM 3644 possessed the most potent aminogenic ability. The influence of NaCl on the growth and production of BA was dependent on their concentration. Higher salt concentration (≥ 3% w/v) significantly inhibited the production of BA. On the contrary, the addition of 1–2% of NaCl w/v significantly improved the production of BA by three tested strains of L. reuteri (CCM 3642, 3644, and 3645). Finally, to better describe the production of BA over time, the relations between selected variables were calculated using linear regression. The appropriate fitting and the corresponding equations suggested the polynomial (degree 2) or exponential relations between the increasing concentration of NaCl and the concentration or calculated specific production rates of produced BA.