Bacteria cultured in space are more deadly

It turns out that a few bacteria can really ruin your space flight. That's why NASA quarantines astronauts several days before their launch.

The National Academy of Sciences reported that bacteria exposed to the microgravity of space are considerably more deadly than their earthbound relatives. During last year's space shuttle Atlantis mission, astronauts brought aboard (on purpose) infectious Salmonella bacteria to see how they are affected by microgravity. When the space-tourist bacteria returned to Earth, they were injected into mice. Mice exposed to space bacteria were three times more likely to die from the Salmonella infection than the control mice, which were injected with earthbound Salmonella.

The most likely explanation for this dwells along the outer cell walls of the bacteria. It is thought that microgravity reduces fluid shear - the movement of liquid around the bacterium cells. Low fluid shear conditions are what the cells experience when they are in the human body. It was also observed that the low fluid shear stimulated the expression of the gene Hfq, which scientists are now fingering as the key to Salmonella's increased strength.

Couple microgravity's affect on bacteria with the fact that microgravity is also known to weaken the human immune system, and it creates a perfect storm for bacteria to attack space travelers. link