Potencial probiótico de microrganismos isolados de grãos de kefir: uma análise in vitro

Abstract

Kefir is a fermented drink produced by fermentation of milk by kefir grains which contain a complex multispecies microbial community formed mainly of lactic acid bacteria (LAB), acetic acid bacteria (AAB), and yeast. High in nutrients, it is a rich and diverse probiotic source. Several studies have shown the benefits of kefir consumption on gut microbiota composition. However, the microbial interactions during the formation of kefir grains and the biotechnological potential of this beverage are not completely understood yet. The aim of this study was to analyze the probiotic potential of microorganisms isolated from kefir grains. Microorganisms isolated from kefir grains were identified, and the tolerance profile to acid pH and sodium chloride (NaCl) was carried out. The self-aggregation and co-aggregation assays were also conducted, using Escherichia coli ATCC and Klebsiella pneumoniae ATCC 700603 as indicator strains. In addition, the antimicrobial potential of the isolated strains was determined by the agar well diffusion technique against indicator strains. Four microorganisms were isolated and identified as Enterococcus durans, Lactobacillus paracasei, Leuconostoc pseudomesenteroides and Kluyveromyces marxianus. With respect to the tolerance tests, no growth was observed at pH 2, 3 and 5, except L. paracasei and K. marxianus at pH 5, while all strains showed resistance at a concentration of 2% of NaCl, except L. pseudomenteroides. High self-aggregation was observed for K. marxianus, whereas E. durans, L. paracasei, L. pseumesenteroides showed moderate capacity. When the indicator strains were added, the percentage of co-aggregation with K. marxianus significantly reduced. Meanwhile, only the K. pneumoniae strain interfered in the aggregation response of L. paracasei. Regarding to the antimicrobial activity, all supernatants, when neutralized, were able to inhibit the growth of the indicator strains. In sum, the microbial isolates obtained from kefir grains showed probiotic properties, with emphasis on L. paracasei and K. maxianus, which showed a greater tolerance to acid pH and a strong capacity for self-aggregation and co-aggregation. It is important to highlight the strong antimicrobial action of L. paracasei against E. coli and K. pneumoniae, which suggests its ability to establish an intestinal barrier against these pathogens. However, these isolates must be subjected to experimental validation in animal models and subsequent clinical trial in humans to confirm their probiotic potential.