Survivability of Kluyveromyces marxianus Isolated From Korean Kefir in a Simulated Gastrointestinal Environment

Safety aspects and in vitro probiotic assessment of Kluyveromyces marxianus strains from neonatal faeces

The isolation and identification of probiotic yeasts is increasing rapidly. In this context, the present study aimed to isolate and identify yeast strains from neonatal faeces in Erzurum province, Türkiye and to determine their probiotic characteristics. A total of 12 yeast strains were isolated and genotypic characterization revealed the presence of seven different species, including Kluyveromyces marxianus, Candida spp. Clavispora lusitaniae, Geotrichum candidum, Trichophyton rubrum, Pichia cactophila, and Meyerozyma guilliermondii. The non-pathogenic and potentially probiotic characteristics of the K. marxianus M2, M9, and M10 strains were further investigated. Although yeast has been isolated from neonatal faeces before, K. marxianus was isolated for the first time in this study. The results revealed that the K. marxianus strains exhibited high resistance to simulated gastric juice and bile salts. The auto-aggregation percentages of the strains ranged from 92.55 to 94.78% after 4 h, while the co-aggregation percentages with pathogens ranged from 19.70 to 53.09%. The K. marxianus M2 strain exhibited the highest degree of hydrophobicity (74.97%), and none of the strains demonstrated DN-ase or haemolytic activity. Furthermore, M2 and M9 strains displayed bile salt hydrolase activity. In conclusion, based on in vitro probiotic test results, K. marxianus strains were selected as probiotic yeast candidates for further studies, especially in patients under antibiotic therapy.

In vitro fermentation characteristics of dietary fibers using fecal inoculum from dogs consuming commercial or grain kefir

Traditional grain kefir is produced from the fermentation of milk with yeast- and bacteria-containing cultures. To maintain consistency and adhere to food safety guidelines, commercial kefir products are based on starter bacterial cultures. Bacterial profiles of starter vs. grain kefirs differ, and their influence on health effects is unknown. Our objectives were to determine the in vitro fermentation characteristics of common dietary fibers using fecal inoculum from dogs supplemented with kefir or kefir bacterial culture as inoculum. Healthy adult dogs were allotted to one of 3 treatments and supplemented for 14 d (n = 4/treatment): 1) 2% reduced-fat milk treated with lactase (CNTL), 2) starter kefir (S-Kefir), or 3) grain kefir (G-Kefir). After 14 d, fresh fecal samples were collected and frozen in a 20% glycerol solution. For the in vitro experiment, fecal samples were thawed, diluted in an anaerobic diluting solution, and used to inoculate tubes containing semi-defined medium and either cellulose (CEL), pectin (PC), beet pulp (BP), or chicory pulp (CP). Tubes were incubated for 0, 6, 12, or 18 h, with short-chain fatty acids (SCFA), pH, and microbiota measured at each time point. A second in vitro experiment was conducted using similar methods and measurements but with S-Kefir and G-Kefir as inoculum sources. Effects of treatment (inoculum), time, and treatment*time interactions within the fiber source were analyzed statistically using Mixed Models and repeated measures, with P < 0.05 being significant. Using fecal inoculum, BP and PC were rapidly fermented, leading to large pH reductions, SCFA increases, and microbiota shifts. pH change was of greater (P < 0.05) magnitude (PC) and higher (P < 0.05) kinetic rate (CP) when using feces from dogs fed S-Kefir or G-Kefir than controls. Butyrate increases were greater (P < 0.05) in tubes inoculated with G-Kefir feces than in S-Kefir or control feces. When PC and BP were fermented, tubes with S-Kefir feces had greater (P < 0.05) acetate, propionate, and total SCFA increases than G-Kefir or control feces. Fermentations were slower when using kefir cultures as inoculum, but some differences were noted. Bacterial beta diversity and relative abundances shifted over time within each substrate and were unique to the inoculum source. Our data suggest that the activity of kefir bacterial populations differs and that kefir consumption changes the abundance and activity of the fecal microbiota of dogs, justifying in vivo investigation.

Characterization and Biological In Vitro Screening of Probiotic Yeast Strains Isolated from Algerian Fruits

Interest in Saccharomyces and non-Saccharomyces yeasts as biotechnological agents is growing worldwide. Here, Kluyveromyces marxianus GBC2 and two Saccharomyces cerevisiae strains FBZ4 and FBK9 were isolated from pomegranate (Punica granatum) and fig (Ficus carica), respectively, and extensively characterized for their probiotic attributes and health benefits. Overall, these strains were found to be γ-hemolytic, non-cytotoxic against Caco-2 cells, and sensitive to therapeutic antifungals. In terms of probiotic characterization, the strains were able to survive at pH 2 and in 1% bile and had high hydrophobicity and self-aggregation properties, which could explain their ability to form biofilm on a polystyrene and adhere to Caco-2 cells. Adhesion rates of 23.52%, 14.05%, and 9.44% were recorded at 37 °C for K. marxianus GBC2, S. cerevisiae FBK9, and S. cerevisiae FBZ4, respectively. Furthermore, biological screening showed a cholesterol assimilation of 54.32% for K. marxianus GBC2 and almost 33% for both Saccharomyces, more than 73% α-amylase inhibition, and good antioxidant potential for all strains; however, only K. marxianus GBC2 showed antibacterial activity against Staphylococcus aureus ATCC 25923. In light of these findings, the strains could be potential candidates for the development of novel functional foods and for probiotic applications.

A comparative evaluation of the kefir yeast Kluyveromyces marxianus A4 and sulfasalazine in ulcerative colitis: anti-inflammatory impact and gut microbiota modulation

Although only Saccharomyces boulardii has been studied for ulcerative colitis (UC), probiotic yeasts have immense therapeutic potential. Herein, we evaluated the kefir yeast Kluyveromyces marxianus A4 (Km A4) and its anti-inflammatory effect with sulfasalazine in BALB/c mice with dextran sulfate sodium (DSS)-induced colitis. Oral administration continued for 7 days after the mice were randomly divided into seven groups: control (CON, normal mice administered with saline), DSS-induced colitis mice administered saline (DSS), and DSS-induced colitis mice administered sulfasalazine only (S), Km A4 only (A4), Km A4 plus sulfasalazine (A4 + S), S. boulardii ATCC MYA-796 (Sb MYA-796) only (Sb), and Sb MYA-796 plus sulfasalazine (Sb + S). The β-glucan content of Km A4 was significantly higher than that of Sb MYA-796 (P < 0.05). Body weight gain (BWG) significantly correlated with colon length, cyclooxygenase-2 (Cox-2) levels, and Bacteroides abundance (P < 0.05). In colitis-induced mice, the A4 + S group had the lowest histological score (6.00) compared to the DSS group (12.67), indicating the anti-inflammatory effects of this combination. The A4 + S group showed significantly downregulated expression of interleukin (Il)-6, tumor necrosis factor-α (Tnf-α), and Cox-2 and upregulated expression of Il-10 and occludin (Ocln) compared to the DSS group. Mice treated with A4 + S had enhanced Bacteroides abundance in their gut microbiota compared with the DSS group (P < 0.05). Bacteroides were significantly correlated with all colitis biomarkers (BWG, colon length, Il-6, Tnf-α, Il-10, Cox-2, and Ocln; P < 0.05). The anti-inflammatory effects of Km A4 could be attributed to high β-glucan content and gut microbiota modulation. Thus, treatment with Km A4 and sulfasalazine could alleviate UC.

Evaluation of the probiotic, technological, safety attributes, and GABA-producing capacity of microorganisms isolated from Iranian milk kefir beverages

Introduction

Kefir beverage has beneficial microorganisms that have health-giving properties; therefore, they have a good potential to be probiotic. This study evaluated the probiotic potential, technological, and safety characteristics of Enterococcus faecalis, Lactococcus lactis, and Pichia fermentans isolated from traditional kefir beverages.

Method

First, isolates were evaluated in terms of resistance to acid, alkali, bile salts, trypsin, and pepsin of the gastrointestinal tract. The auto-aggregation and co-aggregation ability of isolates were measured using spectrophotometry. Antimicrobial activities were assayed against important food-borne pathogens using the agar well diffusion method. Moreover, gamma-aminobutyric acid (GABA) production was investigated by thin-layer chromatography (TLC).

Result

Among the isolates, P. fermentans had an 85% total survival rate, but its amount reached below 6 log CFU/ml which is considered non-resistant, and it showed the highest auto-aggregation (74.67%). Moreover, only L. lactis showed antimicrobial activity and had the highest co-aggregation with E. coli PTCC 1338 (54.33%) and L. monocytogenes ATCC 7644 (78%). Finally, an evaluation of the technological and safety characteristics of the strains showed that the strains produced GABA and were safe.

Discussion

Although the isolates were not resistant to the gastrointestinal tract, their supernatant contained valuable natural compounds, including antioxidants, GABA, and antimicrobials, which can be used to produce functional foods and medicines. In addition, other approaches, such as increasing the initial number of strains, using foods as carriers of isolates, and encapsulating the isolates, can effectively increase the survivability of isolates in the gastrointestinal tract.

Stress response and adaptation mechanisms in Kluyveromyces marxianus

Kluyveromyces marxianus is a non-Saccharomyces yeast that has gained importance due to its great potential to be used in the food and biotechnology industries. In general, K. marxianus is a known yeast for its ability to assimilate hexoses and pentoses; even this yeast can grow in disaccharides such as sucrose and lactose and polysaccharides such as agave fructans. Otherwise, K. marxianus is an excellent microorganism to produce metabolites of biotechnological interest, such as enzymes, ethanol, aroma compounds, organic acids, and single-cell proteins. However, several studies highlighted the metabolic trait variations among the K. marxianus strains, suggesting genetic diversity within the species that determines its metabolic functions; this diversity can be attributed to its high adaptation capacity against stressful environments. The outstanding metabolic characteristics of K. marxianus have motivated this yeast to be a study model to evaluate its easy adaptability to several environments. This chapter will discuss overview characteristics and applications of K. marxianus and recent insights into the stress response and adaptation mechanisms used by this non-Saccharomyces yeast.

Enhanced probiotic potential of Lactobacillus kefiranofaciens OSU-BDGOA1 through co-culture with Kluyveromyces marxianus bdgo-ym6

Introduction

Due to the increasing consumer demand for the development and improvement of functional foods containing probiotics, new probiotic candidates need to be explored as well as novel means to enhance their beneficial effects. Lactobacillus kefiranofaciens OSU-BDGOA1 is a strain isolated from kefir grains that has demonstrated probiotic traits. This species is the main inhabitant of kefir grains and is responsible for the production of an exopolysaccharide (EPS) whit vast technological applications and potential bioactivities. Research has shown that interkingdom interactions of yeast and lactic acid bacteria can enhance metabolic activities and promote resistance to environmental stressors.

Methods

Comparative genomic analyses were performed to distinguish OSU-BDGOA1 from other strains of the same species, and the genome was mined to provide molecular evidence for relevant probiotic properties. We further assessed the cumulative effect on the probiotic properties of OSU-BDGOA1 and Kluyveromyces marxianus bdgo-ym6 yeast co-culture compared to monocultures.

Results

Survival during simulated digestion assessed by the INFOGEST digestion model showed higher survival of OSU-BDGOA1 and bdgo-ym6 in co-culture. The adhesion to intestinal cells assessed with the Caco-2 intestinal cell model revealed enhanced adhesion of OSU-BDGOA1 in co-culture. The observed increase in survival during digestion could be associated with the increased production of EPS during the late exponential and early stationary phases of co-culture that, by enhancing co-aggregation between the yeast and the bacterium, protects the microorganisms from severe gastrointestinal conditions as observed by SEM images. Immune modulation and barrier function for recovery and prevention of flagellin-mediated inflammation by Salmonella Typhimurium heat-killed cells (HKSC) in Caco-2 cells were also measured. OSU-BDGOA1 in mono- and co-culture regulated inflammation through downregulation of pro-inflammatory cytokine expression and increased membrane barrier integrity assessed by TEER, FD4 permeability, and expression of tight junctions.

Discussion

The results of the study warrant further research into the application of co-cultures of yeast and LAB in functional probiotic products and the potential to increase EPS production by co-culture strategies.