Pathogenic or Beneficial?
Some of our most potent tormenters come from among the enterobacteria. Yet we live daily with trillions of harmless, even beneficial enterobacteria in our intestines. The line between the dangerous pathogens and their disarmed relatives is small. How does one tell the difference between the two?

The anwer might lie with bacteriophages. Bacteriophages are viruses that infect bacteria. Just as microbes both plague us and serve us well, so do their submicrobial tormenters (bacteriophages) also bring them benefit. Unfortunately, in some cases, benefit to bacteria means ill fortune for us: bacteriophage may provide bacteria with a gene that makes the difference between a harmless wayfarer and potent pathogen.

Ironically, one route towards understanding the pathogenicity of bacteria is identifying their own pathogens.

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