Man's best friend

New take on infection-causing bugs

Paul Blow


Bacteria are bad. Parents and doctors, not to mention the cleaning product industry, warn of their dangers. But a Stanford microbiologist has an intriguing suggestion:

Bacterial and viral infections have benefits.

Professor Stanley Falkow, PhD, a renowned microbiologist (and noted bacterial sympathizer — he says he tries to “think like a bacterium”), wonders if medical researchers’ obsession with stamping out infections distracts them from appreciating micro-organisms’ contributions.

“The fact is,” says Falkow, “a great number of organisms that infect humans come in and set up housekeeping, as it were. There are no clinical symptoms of anything wrong, and people take the organisms with them to their graves.”

The best recent example of this, says Falkow, is Helicobacter pylori. The bug earned researchers the 2005 Nobel Prize in Medicine or Physiology for implicating it as a cause of ulcers and stomach cancer. As is typical in microbiology, though, it’s not a simple equation. Being infected does not always equal ulcers or cancer. At least 80 percent of the world’s population is infected with H. pylori yet has no overt symptoms.

As advances such as clean water and pasteurization are adopted, the prevalence of H. pylori infection declines. What makes the study of H. pylori even more perplexing is that on the one hand, this decline has been accompanied by a drop in the incidences of gastric cancer and ulcers. On the other, there has been an increase in esophageal cancer. H. pylori infection appears to protect against cancer of the esophagus — something professor Julie Parsonnet, MD, has documented extensively.

So by messing with the microbes, are we just replacing one disease with another?

Falkow’s lab has been studying the phenomenon of persistent infection for decades, in particular with H. pylori and Salmonella. The lab’s researchers have shown that even after the mice have fought off the infection, a few of these organisms remain in the mice.

“It’s not so much that the immune system has failed,” Falkow explains, “but that the organisms have manipulated the immune system in such a way that they can’t be cleared.” If researchers use antibiotics to eliminate infection completely, the mice are highly susceptible to re-infection, and the re-infection is more likely to progress to disease.

Furthermore, in humans, as infectious diseases have decreased, autoimmune disorders such as ulcerative colitis, Crohn’s disease and diabetes have increased.

“All these observations have been made without necessarily trying to pull it all together,” says Falkow, the Robert W. and Vivian K. Cahill Professor in Cancer Research. So he wrote an article in the Feb. 24 issue of the journal Cell to get other scientists thinking about our microbial relationships.

He suspects that one reason the immune system tolerates infection is that — at least in some cases — it’s good for us. But that’s just a speculation, he admits. More scientists need to study the connections between infection and good health. They should dig in to the topic. Get their hands dirty, he says. Really dirty.

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