When poet Walt Whitman wrote that we "contain multitudes," he was speaking metaphorically — but he was correct in the literal sense. Every human being carries over 100 trillion individual bacterial cells within the intestine — ten times more cells than comprise the body itself. The commensal relationship that develops between humans and internal bacteria is one in which both humans and bacteria derive benefits. Researchers from the Perelman School of Medicine at the University of Pennsylvania are exploring the microbiome and its influence on human health and disease.
Unlike the harmful microbes that cause illness, the bacteria, viruses, and eukaryotic organisms that comprise the microbiome help us digest food, protect our skin from unwanted invaders, and otherwise thrive in a complex environment. Penn researchers and other scientists are only now beginning to tease out who these bugs are and how they interact with human cells and systems. Read more.
Humans rely on commensal bacteria for numerous tasks, but even normally helpful bacteria can cause trouble when they end up somewhere they shouldn't be. Our immune system and other cells have evolved ways to control the microbes, and sometimes the microbes help keep the immune system in check. Read more.
Microbes can have many different personalities. In some forms, they coexist peacefully with their host. In other forms, they turn deadly. Researchers are starting to learn how the bacteria and viruses in our microbiome evolve from one state to another. Read more.