The Microbial Revolution: Unveiling the Human Microbiome

The term "Microbiome," coined by Joshua Lederberg in 2001, encompasses all the microbes and their collective genetic material residing within or on the human body. In 2012, the Human Microbiome Project (HMP) made a significant discovery—microbes, not human cells, are the predominant inhabitants of the human body, outnumbering human cells tenfold and comprising 1-3 percent of a person's total body mass, equivalent to 2-6 pounds (0.9-2.7 kilograms). Furthermore, bacteria possess a staggering 360 times more protein-coding genes than the human genome, boasting around eight million.

Enterococci, as depicted here in color, naturally reside in the intestines of both humans and animals. However, they can also pose a significant threat by causing severe infections, especially in healthcare environments. What's most alarming is that enterococci exhibit inherent or acquired resistance to numerous antibiotics.

The completion of the Human Genome Project in 2006 facilitated the differentiation of human and microbial genes. In 2008, the US National Institutes of Health initiated the HMP, a five-year study aimed at characterizing the microbial population within healthy human bodies, establishing a reference database, and investigating whether variations in these populations predispose individuals to diseases. Researchers identified approximately 10,000 microbial species, predominantly bacteria but also including protozoa, yeasts, and viruses. As of June 2012, they had identified 81-99 percent of these species. The highest microbial concentrations are found on or within the skin, genital area, mouth, and notably, the intestines. Predictably, microbial populations exhibit the greatest similarity within similar body regions. Moreover, the microbial composition undergoes changes over time, influenced by factors such as disease and medications, particularly antibiotics.

In earlier times, identifying microbes required labor-intensive isolation and culture growth. However, the HMP employed DNA sequencing technology, alongside computer analysis of genome sequences using bacterial ribosomal RNA (16S rRNA)—a feature unique to bacteria—and phylogenetic studies for microbial classification and identification.

Contrary to the previous belief that the human body solely maintained its health independently, it is now acknowledged that certain microbes play an indispensable role in digestion and nutrient absorption. Additionally, they contribute to the synthesis of vitamins, natural anti-inflammatory substances, and the metabolism of drugs and other foreign chemicals within the human body.