Use of Antibiotics and Mortality in Women: Does Duration of Exposure Matter?

The integrity of microorganisms which reside in the human gut (gut microbiota) is important for our health and survival. The human intestine contains about 1014 microbes, 10× the number of cells in the entire body.1 Overall, these microorganisms have a biomass of about 1.5 kg1 and contain >5 million genes (gut microbiome), >100× those in the host.2 Gut microbiome has an intense enzymatic and metabolic production that equals that of the liver.2 These microbes are obligatory anaerobes for >99%, belong to 500 to 1000 diverse species, and their density progressively increases from the stomach (101 bacteria per gram of stomach) to colon (107 bacteria per gram of colon).3 Firmicutes and Bacteroides are the most prevalent species. Some of these microorganisms reside in the lumen, while others adhere to mucus or directly to the gut epithelium. Notably, >60% of these bacteria cannot be identified by stool culture, thereby requiring complex DNA sequencing techniques. Colonization of the host’s gut by microbes starts at birth during transit in the birth canal and through bacteria present in the mother’s milk.1 The composition of the gut microbiota varies not only among host species, but also among different individuals, and is importantly affected by diet.3