The gut microbiota is emerging as a promising target for the management or prevention of inflammatory and metabolic disorders in humans. Many of the current research efforts are focused on the identification of specific microbial signatures, more particularly for those associated with obesity, type 2 diabetes, and cardiovascular diseases. Some studies have described that the gut microbiota of obese animals and humans exhibits a higher Firmicutes/Bacteroidetes ratio compared with normal-weight individuals, proposing this ratio as an eventual biomarker. Accordingly, the Firmicutes/Bacteroidetes ratio is frequently cited in the scientific literature as a hallmark of obesity. The aim of the present review was to discuss the validity of this potential marker, based on the great amount of contradictory results reported in the literature. Such discrepancies might be explained by the existence of interpretative bias generated by methodological differences in sample processing and DNA sequence analysis, or by the generally poor characterization of the recruited subjects and, more particularly, the lack of consideration of lifestyle-associated factors known to affect microbiota composition and/or diversity. For these reasons, it is currently difficult to associate the Firmicutes/Bacteroidetes ratio with a determined health status and more specifically to consider it as a hallmark of obesity.

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The gut microbiota is currently recognized as an important factor regulating the homeostasis of the gastrointestinal tract and influencing the energetic metabolism of the host as well as its immune and central nervous systems. Determining the gut microbiota composition of healthy subjects is therefore necessary to establish a baseline allowing the detection of microbiota alterations in pathologic conditions. Accordingly, the aim of this study was to characterize the gut microbiota of healthy Chilean subjects using 16S rRNA gene sequencing. Fecal samples were collected from 41 young, asymptomatic, normal weight volunteers (age: 25 ± 4 years; ♀:48.8%; BMI: 22.5 ± 1.6 kg/m2) with low levels of plasma (IL6 and hsCRP) and colonic (fecal calprotectin) inflammatory markers. The V3-V4 region of the 16S rRNA gene of bacterial DNA was amplified and sequenced using MiSeq Illumina system. 109,180 ± 13,148 sequences/sample were obtained, with an α-diversity of 3.86 ± 0.37. The dominant phyla were Firmicutes (43.6 ± 9.2%) and Bacteroidetes (41.6 ± 13.1%), followed by Verrucomicrobia (8.5 ± 10.4%), Proteobacteria (2.8 ± 4.8%), Actinobacteria (1.8 ± 3.9%) and Euryarchaeota (1.4 ± 2.7%). The core microbiota representing the genera present in all the subjects included Bacteroides, Prevotella, Parabacteroides (phylum Bacteroidetes), Phascolarctobacterium, Faecalibacterium, Ruminococcus, Lachnospira, Oscillospira, Blautia, Dorea, Roseburia, Coprococcus, Clostridium, Streptococcus (phylum Firmicutes), Akkermansia (phylum Verrucomicrobia), and Collinsella (phylum Actinobacteria). Butyrate-producing genera including Faecalibacterium, Roseburia, Coprococcus, and Oscillospira were detected. The family Methanobacteriaceae was reported in 83% of the subjects and Desulfovibrio, the most representative sulfate-reducing genus, in 76%. The microbiota of the Chilean individuals significantly differed from those of Papua New Guinea and the Matses ethnic group and was closer to that of the Argentinians and sub-populations from the United States. Interestingly, the microbiota of the Chilean subjects stands out for its richness in Verrucomicrobia; the mucus-degrading bacterium Akkermansia muciniphila is the only identified member of this phylum. This is an important finding considering that this microorganism has been recently proposed as a hallmark of healthy gut due to its anti-inflammatory and immunostimulant properties and its ability to improve gut barrier function, insulin sensitivity and endotoxinemia. These results constitute an important baseline that will facilitate the characterization of dysbiosis in the main diseases affecting the Chilean population.

SUMMARYHelicobacter pylori is a highly prevalent pathogen considered as an aetiological factor for gastroduodenal ulcers, and a risk factor for gastric adenocarcinoma and lymphoma in humans. Most subjects colonized by this micro-organism are asymptomatic and remain untreated. In symptomatic patients, the antibiotic treatment has a high cost and is not 100% effective because of resistance to antibiotics and to moderate patient compliance. This review discusses the role of probiotics as alternative solutions to assist in the control of H. pylori colonization in atrisk populations.The evidence that some strains of Lactobacillus and Bifidobacterium are able to inhibit H. pylori growth through the release of bacteriocins or organic acids, and may also decrease its adhesion to epithelial cells, is reviewed. In addition, probiotics have a possible role in the stabilization of the gastric barrier function and the decrease of mucosal inflammation. Other aspects that are considered are the contribution of probiotics to the healing of the gastric mucosa linked to their antioxidant and anti-inflammatory properties.Clinical trials in colonized adults and children are reviewed, and suggest that probiotics do not eradicate H. pylori but maintain lower levels of this pathogen in the stomach; in combination with antibiotics, probiotics may increase eradication rate and/or decrease adverse effects. Papers suggesting similar effects on H. pylori by foodstuffs such as berry juice and some milk proteins are quoted. Regular intake of these and other dietary products might constitute a low-cost, large-scale alternative solution applicable for populations at-risk for H. pylori colonization.

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