The establishment and succession of bacterial communities in infants may have a profound impact in their health, but information about the composition of meconium microbiota and its evolution in hospitalized preterm infants is scarce. In this context, the objective of this work was to characterize the microbiota of meconium and fecal samples obtained during the first 3 weeks of life from 14 donors using culture and molecular techniques, including DGGE and the Human Intestinal Tract Chip (HITChip) analysis of 16S rRNA amplicons. Culture techniques offer a quantification of cultivable bacteria and allow further study of the isolate, while molecular techniques provide deeper information on bacterial diversity. Culture and HITChip results were very similar but the former showed lower sensitivity. Inter-individual differences were detected in the microbiota profiles although the meconium microbiota was peculiar and distinct from that of fecal samples. Bacilli and other Firmicutes were the main bacteria groups detected in meconium while Proteobacteria dominated in the fecal samples. Culture technique showed that Staphylococcus predominated in meconium and that Enterococcus, together with Gram-negative bacteria such as Escherichia coli, Escherichia fergusonii, Klebsiella pneumoniae and Serratia marcescens, was more abundant in fecal samples. In addition, HITChip results showed the prevalence of bacteria related to Lactobacillus plantarum and Streptococcus mitis in meconium samples whereas those related to Enterococcus, Escherichia coli, Klebsiella pneumoniae and Yersinia predominated in the 3^rd week feces. This study highlights that spontaneously-released meconium of preterm neonates contains a specific microbiota that differs from that of feces obtained after the first week of life. Our findings indicate that the presence of Serratia was strongly associated with a higher degree of immaturity and other hospital-related parameters, including antibiotherapy and mechanical ventilation.

In previous years, it has been shown that human milk is a potential source of bacteria for the infant gut. The results of this work confirm the presence of the same specific bacterial strains of Bifidobacterium, Lactobacillus, and Staphylococcus in breast milk and infant fecal samples. The identity of bacteria isolated from breast milk and infant feces from 20 mother-infant pairs was investigated at the strain level. DNA from Staphylococcus, Lactobacillus, and Bifidobacterium was detected by qRTi-PCR in nearly all samples analyzed. These samples were cultured on different agar media. One colony representative of each morphology was selected and identified at the species level combining classical tests and molecular techniques (PCR, RAPD, PFGE, and/or MLST genotyping). Breast milk and infant feces from 19 mother-infant pairs shared different Staphylococcus, Lactobacillus, and/or Bifidobacterium species and strains. Significantly, 2 mother-infant pairs shared 4 bacterial strains although most pairs shared 2. These results confirm that breast milk and infant feces from mother-infant pairs share the same strain(s), indicating that breastfeeding could contribute to the bacterial transfer from the mother to the infant and, therefore, to the infant gut colonization.

The human microbiome is emerging as an interesting field in research into the prevention of health problems and recovery from illness in humans. The complex ecosystem formed by the microbiota is continuously interacting with its host and the environment. Diet could be assumed to be one of the most prominent factors influencing the microbiota composition. Nevertheless, and in spite of numerous strategies proposed to modulate the human microbiota through dietary means, guidelines to achieve this goal have yet to be established. This review assesses the correlation between social and dietary changes over the course of human evolution and the adaptation of the human microbiota to those changes. In addition, it discusses the main dietary strategies for modulating the microbiota and the difficulties of putting them properly into practice.

Remyelination is a key aspect in multiple sclerosis pathology and a special effort is being made to promote it. However, there is still no available treatment to regenerate myelin and several strategies are being scrutinized. Myelination is naturally performed by oligodendrocytes and microRNAs have been postulated as a promising tool to induce oligodendrocyte precursor cell differentiation and therefore remyelination. Herein, DSPC liposomes and PLGA nanoparticles were studied for miR-219a-5p encapsulation, release and remyelination promotion. In parallel, they were compared with biologically engineered extracellular vesicles overexpressing miR-219a-5p. Interestingly, extracellular vesicles showed the highest oligodendrocyte precursor cell differentiation levels and were more effective than liposomes and polymeric nanoparticles crossing the blood–brain barrier. Finally, extracellular vesicles were able to improve EAE animal model clinical evolution. Our results indicate that the use of extracellular vesicles as miR-219a-5p delivery system can be a feasible and promising strategy to induce remyelination in multiple sclerosis patients.