But perhaps the most bizarre items are anti-bacterial plastic maracas for that germ-free salsa experience.

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Researchers then transferred samples from the guts of the three groups of mice into other germ-free mice.

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They found that colonizing an adult germ-free animal with normal gut bacteria had no effect on their behavior.

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"Germ-free" mice, born without the bugs and protected from their arrival, have shown a number of effects distinct from mice born in the normal way.

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Only 7% of the bills were germ-free.

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"We know that animals in 'germ-free' conditions can reproduce, they have a longer lifespan, and they seem to live perfectly OK, provided you don't expose them to stress or damage, " said Sven Pettersson, the Karolinska Institute microbiologist who, along with neuroscientist Rochellys Diaz Heijtz, led the research.

BBC: Bacteria in mouse gut affect development and behaviour