The influence of polyols on the bacteriotropic properties of the Lactobacillus reuteri cell-free superants

Abstract

Introduction. Precursor directed biosynthesis is one of the promising approaches to finding new antimicrobial agents and creating next-generation probiotics. L. reuteri is capable to convert triatomic polyol glycerol into reuterine, a broad-spectrum antimicrobial substance. There are no data on the use of other polyols as precursors. The aim of the research was to investigate the effect of cell-free supernatants obtained by culturing L. reuteri DSM 17938 in its own disintegrate, supplemented with polyols (xylitol, sorbitol, mannitol and glycerol & glucose) on the daily biomass growth of opportunistic microorganisms. Material & methods. Reference strains Staphylococcus aureus ATCC 25923; Escherichia coli AТСС 25922 and Pseudomonas aeruginosa clinical isolate were used as a test cultures. The effect of the lactobacillus supernatant on the daily biomass growth of the test cultures was investigated by spectrophotometry using a 96-well polystyrene microtiter plates and a «LisaScanEM» spectrophotometer («ErbaLachemas.r.o.», Czech Republic). The final concentration of supernatants in the incubation medium was 30%, and the final concentration of bacterial cells was ~10⁶ CFU/ml. Inhibition (II) or stimulation (SI) indices of the daily biomass growth of test cultures by formula were calculated. Results & discussion. Supplementation of culture medium with glycerol & glucose during L. reuteri cultivation resulted in the S. aureus (II = 70.7%), Escherichia coli (II = 72.2%) and P. aeruginosa (II = 74.7%) daily biomass growth inhibition. As a result of L. reuteri cultivation in its own disintegrate supplemented with mannitol, the supernatant acquired growth-promoting properties with respect to S. aureus (SI = 45.5%), E. coli (SI = 19.1%) and P. aeruginosa (SI = 19, 9%). The supernatant obtained after L. reuteri cultivation in disintegrate supplemented with sorbitol had no significant effect on the S. aureus and Escherichia coli daily biomass growth, but significantly stimulated the growth of P. aeruginosa (SI = 29.4%). The supernatant of L. reuteri, cultured in disintegrate supplemented with xylitol had no effect on staphylococcus growth, inhibited of E. coli (II = 16.5%) growth and increased of P. aeruginosa (SI = 19.1%) daily biomass growth. The data obtained for glycerol, the introduction of which into the culture medium of L. reuteri led to the appearance of inhibitory activity of the supernatant against all test cultures, were expected. They coincide with the results of studies by other authors and are associated with the ability of this type of lactobacilli to convert glycerol into a broad-spectrum antimicrobial substance reuterin. The results of the study confirm that xylitol, sorbitol and mannitol do not undergo fermentation with the formation of acidic end products during the cultivation of L. reuteri. These polyols remain either unchanged or undergo slight modification in the composition of the supernatant and have different effects on the daily biomass growth of test cultures. Conclusion. The results of the study showed that the use of xylitol, sorbitol and mannitol as precursors, and L. reuteri DSM 17938 as a biotransformer system in the development of new antimicrobials using a precursor-directed biosynthesis strategy is ineffective. They also confirmed that the supernatant obtained after cultivation of L. reuteri DSM 17938 in its own disintegrate supplemented with glycerol & glucose, has a pronounced inhibitory activity against the investigated opportunistic microorganisms.