Just Lookin' for a Home

Abstract

P ity the bacteria that find themselves in the human gut. They must adjust to high temperature and acidity, not to mention competition from other bacteria for food and space. Bile salts bathe them in a powerful detergent. The constant downward squeeze of peristalsis threatens to dislodge them. Many bacteria survive these conditions through sheer tenacity. Adhering tightly to the intestinal lining, they feed and reproduce, developing colonies that cling to inner surfaces of their human hosts like bits of wet tissue paper. Other bacteria make use of the adverse conditions to spur their growth. Some bacteria, such as varieties of the common bacteria Salmonella and Shigella, however, have broken through the barrier posed by the gut. They've found new homes, either by staying within intestinal wall cells or by slipping through those cells to reach quieter niches in other tissues. bacteria that thrive on the surface of the intestines do no harm to their human hosts. Those that penetrate cells, says Stanford University School of Medicine bacteriologist Stanley Falkow, often become pathogens-microorganisms that cause disease. From the bacterial point of view, Falkow says, pathogenicity is simply another facet of their extraordinary versatility. It's survival. It's how the bacteria make a living. From the human point of view, however, this pathogenicity can mean sickness and death. Bacteria often injure cells directly or fan the immune system into a powerful inflammation that does more harm than good. Accordingly, the aim of medical scientists has long centered on wiping out pathogens after a person has become ill. as more bacteria become resistant to antibiotics, a subtler approach might be better. Most of medicine looks at the product of bacterial invasion, at the disease, Falkow says. But disease may be the last thing we want to study; it comes after all the interesting stuff happens. The interesting stuff, according to Falkow, includes how bacteria attach to and enter the cells and how they survive