Bacteria have vastly different survival abilities, says Jeri Barak, an assistant professor of plant pathology
at UW-Madison. Many species normally live in soil or water, but some of
those that live in the human intestinal tract display extreme longevity
outside the body.

Salmonella, which causes what we sometimes call “food poisoning,”
can live more than 400 days in soil. And when dried on a laboratory
slide, salmonella survived for almost three years, says Barak, who
studies salmonella contamination on leafy greens, a growing cause of
gastrointestinal illness.

However, E. coli, another resident of the intestinal tract, tends to die sooner in the environment.

Many bacteria form spores — tough, durable “seeds” that can
withstand extreme abuse. Spores of respiratory anthrax, like that used
in the 2001 bio-terrorism attacks, can survive for many years.

Environmental also conditions affect survival, Barak adds. For
example, the bacterium that causes tuberculosis can be killed by
full-spectrum lights, which contain ultraviolet light. In contrast,
bacteria that live on plants have pigments that block ultraviolet rays,
allowing them to thrive in sunlight.

Finally, bacteria can form communities called “biofilms” that
greatly increase their ability to survive adverse conditions. Biofilms
can be a major problem on catheters and other medical devices, because
measures that kill the outer layers of bacteria may not affect those
located deeper inside the biofilm