It sounds like the plot for a scary B-movie: Germs go into space on a rocket and come back stronger and deadlier than ever.

Except it really happened.

The germ: Salmonella, best known as a culprit of food poisoning.

The trip: Space Shuttle STS-115, September 2006.

The reason: Scientists wanted to see how space travel affects germs, so they took some along — carefully wrapped — for the ride.

The result: Mice fed the space germs were three times more likely to get sick and died quicker than others fed identical germs that had remained behind on Earth.

The researchers found that 167 genes had changed in the salmonella that went to space.

Why?

"That’s the $64 million question," Nickerson said. "We do not know with 100 percent certainty what the mechanism is of space flight that’s inducing these changes."

The results of the salmonella study are reported in yesterday’s edition of Proceedings of the National Academy of Sciences.