Research background. Kefir is a natural probiotic drink traditionally produced by milk fermentation using kefir grains. Kefir grains are composed of a complex population of bacteria and yeasts embedded in a polysaccharide-protein matrix. The geographic origin of kefir grains may largely influence their microbial composition and the associated kefir drink properties. Although the detailed bacterial composition of kefir grains from several geographic regions has been reported, to date, analogous data about the microbiome of Greek kefir are lacking. Hence, the aim of this study is to investigate the structure and the diversity of the bacterial community of Greek kefir grains.Experimental approach. The bacterial community structure and diversity of two different kefir grains from distant geographic regions in Greece were examined via high-throughput sequencing analysis, a culture-independent metagenomic approach, targeting the 16S rRNA V4 variable region, in order to gain a deeper understanding of their bacterial population diversities.Results and conclusions. Firmicutes (a phylum that includes lactic acid bacteria) was strikingly dominant amongst the identified bacterial phyla, with over 99 % of the sequences from both kefir grains classified to this phylum. At the family level, Lactobacillaceae sequences accounted for more than 98 % of the operational taxonomic units (OTUs), followed by Ruminococcaceae, Lahnospiraceae, Bacteroidaceae and other bacterial families of lesser abundance. Α relatively small number of bacterial genera dominated, with Lactobacillus kefiranofaciens being the most abundant in both kefir grains (95.0 % of OTUs in kefir A and 96.3 % of OTUs in kefir B). However, a quite variable subdominant population was also present in both grains, including bacterial genera that have been previously associated with the gastrointestinal tract of humans and animals, some of which are believed to possess probiotic properties (Faecalibacterium spp., Bacteroides spp., Blautia spp.). Differences among the bacterial profiles of the two grains were very small indicating a high homogeneity despite the distant geographic origin.Novelty and scientific contribution. This is the first study to deeply explore and report on the bacterial diversity and species richness of Greek kefir.

The objective of this study was twofold: i) to examine the effect of early-posthatch dietary inclusion of the clay mineral palygorskite on laying pullets’ growth and ii) to determine the potential effects of the latter diet on cecal microbial communities. Four hundred and thirty two female, day old Hyline Brown chickens were equally and randomly allocated to two dietary treatment groups; control and palygorskite (0% and 0.5% palygorskite, respectively). They were reared in floor pens for eighteen weeks. Feed intake, feed conversion ratio, body weight gain and uniformity were assessed. At the end of the rearing period, fifty three birds per group were transferred to laying cages without any changes in their respective dietary treatments. At onset of lay, eight birds from each group were euthanized and their ceca were obtained for analysis. Culture-independent and sequencing-based methods were used to analyse cecal microbial composition. Palygorskite dietary supplementation increased the uniformity of the relative group at the end of the rearing period. Pullets that received palygorskite had different and more homogeneous cecal microbial profiles at onset of lay when compared to controls. Moreover, in the ceca of the former pullets a more favorable microbiota was evident; it comprised largely of bacteria that are major degraders of resistant polysaccharides and efficient in butyrate production. The novelty of the present study lies to the beneficially effect of palygorskite (a clay mineral) to pullets growth and health, likely through modulation of the gut microbiota.

Periodontitis, a chronic inflammatory disease affecting the supporting tissues of the teeth, has been linked to the onset of neurological diseases, including Alzheimer’s disease (AD). A primary mechanism connecting these two issues is oxidative stress caused by an imbalance between antioxidant defenses and reactive oxygen species (ROS) synthesis. This review compiles results from both animal and human studies that explore how oxidative stress resulting from periodontitis leads to neuroinflammation, mitochondrial dysfunction, and cognitive decline in AD. Studies in animals indicate that periodontal infections worsen brain oxidative damage, as evidenced by elevated lipid peroxidation markers, such as malondialdehyde (MDA), and indicators of oxidative DNA damage, including 8-hydroxy-2′-deoxyguanosine (8-OHdG). Additionally, significant reductions in crucial antioxidant enzymes, including superoxide dismutase (SOD) and glutathione peroxidase, along with neuroinflammation and cognitive deficits, are observed in mouse models of induced periodontitis. Supporting evidence from human studies reveals lower total antioxidant capacity (TAC) in individuals with both Alzheimer’s disease (AD) and periodontitis, as well as increased systemic oxidative stress markers, such as advanced oxidation protein products (AOPRs). These findings suggest a mechanistic relationship through oxidative stress pathways between periodontal inflammation and neurodegeneration. Given the extensive impact of periodontitis, enhancing periodontal health could be a viable strategy to reduce oxidative damage and lower the risk of cognitive decline. Further research is needed to clarify causality and to investigate antioxidant treatments aimed at preventing or slowing the progression of AD in patients with periodontal disease.

This study aimed to evaluate the behavior of Listeria monocytogenes during the manufacture and storage of artisanal kefir. A five-strain cocktail of L. monocytogenes was introduced (at ca. 3.0 log₁₀ CFU/mL) into UHT milk as a pre-fermentation contaminant. The growth of L. monocytogenes, lactic acid bacteria and yeasts was monitored during the 24-h fermentation period of milk with two types of kefir grains at 20 °C and the subsequent storage of kefir under adequate (4 °C) and inadequate (10 °C) refrigerated-storage conditions. L. monocytogenes grew into much higher cell densities (5.3–5.8 log₁₀ CFU/mL) by the end of the fermentation period, but the final (24-h) counts were substantially lower than those obtained in the corresponding control trials with unfermented milk (7.2 log₁₀ CFU/mL). The growth rate of L. monocytogenes during fermentation differed depending on the type of kefir grain used. During the subsequent 11-day storage of the kefir filtrates at 4 °C or 10 °C, the behavior of L. monocytogenes varied from no growth to further population increases (of up to 1.1 log₁₀ CFU/mL), depending on the storage temperature, but also depending on the type of kefir grain and the grain surface-to-weight ratio that had been used to ferment the milk. This study highlights the need for strict adherence to good hygiene practices during artisanal kefir making and shows that L. monocytogenes can sustain considerable growth during milk fermentation and further grow during the subsequent cold storage of kefir, particularly under inadequate refrigerated storage conditions.