"They're quite specialized, the pathogenic bacteria. Each one recognizes a specific kind of host cell and does a specific thing. Each one has its own gimmick, as it were, to be successful."

The plague bacillus, which Falkow also studies, enters the cell very differently than Salmonella. First, it attaches to little spikes, called phylopodia, on the surface of a host cell. Its target is the epithelial cells that line the stomach and gut. Once attached, the cell slurps up the bacteria like spaghetti.


With little muss or fuss, the plague bacillus slips into a human cell. Video provided by Stanley Falkow. 2.4 Megabyte QuickTime Movie. Click on the image to view.

Stanley Falkow answers the question, "Are bacteria out to get us?"
Certain strains of e. coli bacteria have a much different strategy for survival. These bacteria never enter a host cell. Instead, they attach to the outside of the cell and induce the host to build them a tiny "throne" on the cell wall. From their throne, they send chemical messages through the cell wall that induce the host to bathe them in water and nutrients. If the host cells are in the intestine, we notice this bacteria bath as diarrhea. Usually a minor inconvenience for adults, in many parts of the world diarrhea, and the dehydration it causes, can be deadly to infants and children.

"The bacteria live in the gut, which is a place of privilege. It must be very nice for them, because what you see on the surface of the cell is the growth of colonies of bacteria. Even though they never go in, they subvert the host cell's biochemistry for their own betterment," says Falkow.

In the process, one strain of e. coli also secretes a potent toxin that causes bleeding in the small intestine. This strain was behind the recent deadly outbreak of food poisoning in the Pacific Northwest from eating undercooked hamburger.

By spying on the microscopic war between pathogens and their hosts, Falkow and his colleagues hope to eventually disarm the microbes' weapons by developing new vaccines or antibiotics. "It's really an exciting time now," says Falkow, "because we're getting to understand more about the strategies pathogens use during infection. In the process, we learn as much about host cell biology as we do about bacterial biology."


Microbe Spy


Bottom Bar

©1997 Exploratorium