The human intestine is populated by approximately 1014 microscopic unicellular bacteria, living organisms, many of which are beneficial. All the bacteria living in the intestinal flora, which also contains viruses and fungi, constitute the gut microbiota and belong mainly to the phylum Firmicutes and Bacteroidetes.
Firmicutes are so-called “Gram-positive” bacteria, classified by the color they turn in the Gram’s staining method, which determines the bacterial classification and taxonomy, and is based on precise characteristics.
Firmicutes are divided into different classes including: Clostridia (class of bacteria for which oxygen is toxic), Mollicutes (class of tiny parasitic bacteria with no cell wall), Bacilli (where you find, among others, Bacillus, Listeria, Staphylococcus) and Lactobacillales (class of lactic acid bacteria)
The most famous Bacteroidetes are the bacteria belonging to the Bacteroidales, present in animal and human faeces, and to the Porphyromonas coming from human oral cavity.
The balance or proportion between Firmicutes and Bacteroides, is primordial. But when it is disrupted, this is where gut dysbiosis occurs, can cause many health problems and diseases.