Bacteria are bad. Mothers and doctors, not to mention the cleaning product industry, repeatedly warn of their dangers. But a Stanford University School of Medicine microbiologist is raising the intriguing idea that persistent bacterial and viral infections have benefits.
Stanley Falkow, PhD, the Robert W. and Vivian K. Cahill Professor in Cancer Research, published his thoughts on this topic in an essay in the Feb. 24 issue of the journal Cell, in which he asks, "Is persistent bacterial infection good for your health?" The essay is based on a talk he was invited to give at Cambridge University in November.
Falkow points out that the medical community and those who fund medical research focus on curing disease. He wonders if this single-mindedness might distract researchers from appreciating the beneficial contributions of micro-organisms to the body.
"Organisms that cause disease are usually considered in the context of harm and epidemics and so on," said Falkow. "But the fact is that 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."
It's not that the organisms in question - such as the bacteria that cause pneumonia or meningitis - are innocuous, he said. It's just that most of the individuals do not get disease from being infected.
The best recent example of this, said Falkow, is H. pylori. First identified only 25 years ago, the organism earned researchers last year's Nobel Prize in Medicine or Physiology for being implicated as a cause of ulcers and stomach cancer.
As is typical in the world of microbiology, though, it's not a simple equation: being infected = ulcers or cancer. At least 80 percent of the world's population is infected with H. pylori yet has no overt symptoms.
What makes the study of H. pylori even more perplexing is that as such advances as clean water and pasteurization are adopted, the prevalence of H. pylori infection has declined. On the one hand, this has been accompanied by a drop in the incidence of gastric cancer and ulcers. On the other, there has been an increase in esophageal cancer. H. pylori appear to protect against cancer of the esophagus. "So that says that there might be something about persistent infection that might be protective," said Falkow.
This raises the conundrum: 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. He and his colleagues have shown that when infected with these organisms, mice initially show an inflammatory response that then settles down and stays with them for the rest of their lives.