A proposal for the reference intervals of the Italian microbiota 'scaffold' in healthy adults

Numerous factors, ranging from genetics, age, lifestyle, and dietary habits to local environments, contribute to the heterogeneity of the microbiota in humans. Understanding the variability of a “healthy microbiota” is a major challenge in scientific research. The gut microbiota profiles of 148 healthy Italian volunteers were examined by 16S rRNA gene sequencing to determine the range and diversity of taxonomic compositions in the gut microbiota of healthy populations. Possible driving factors were evaluated through a detailed anamnestic questionnaire. Microbiota reference intervals were also calculated. A “scaffold” of a healthy Italian gut microbiota composition was identified. Differences in relative quantitative ratios of microbiota composition were detected in two clusters: a bigger cluster (C2), which included 124 subjects, was characterized by more people from the northern Italian regions, who habitually practised more physical activity and with fewer dietary restrictions. Species richness and diversity were significantly higher in this cluster (C2) than in the other one (C1) (C1: 146.67 ± 43.67; C2: 198.17 ± 48.47; F = 23.40; P 1: 16.88 ± 8.66; C2: 35.01 ± 13.40; F = 40.50; P