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We keep foodstuffs in the fridge to reduce bacterial spoilage but are there any bacteria that thrive best at fridge temperatures? Are some foodstuffs more likely to spoil in the fridge rather than out of it because they carry such bacteria?

• The temperature inside a refrigerator should be kept between 1 and 4 °C – cold enough to slow the metabolism and reproduction of most bacteria while not causing water to freeze, which ruptures cells and damages food.

However, there are so-called psychrotrophic bacteria – including and – that can reproduce at these temperatures. This led researchers in France to the controversial suggestion that Crohn’s disease, in which the gastrointestinal tract becomes inflamed, is on the rise because of the increased use of refrigerators (The Lancet, vol 362, p 2012).

At 0 °C, even the growth of psychrotrophic bacteria comes to a virtual halt, but microbial activity does not stop altogether. At -2 °C the plant pathogen is still able to make proteins that help water freeze. These can damage fruit and vegetables by causing ice crystals to form near the walls of epithelial cells.

Now consider that bacteria like , and have been revived after many thousands of years in suspended animation, locked in ice. The finding has encouraged astrobiologists investigating the possibility of extraterrestrial life. Some believe in panspermia, the idea that bacteria can survive a voyage through space and can seed life wherever conditions are suitable. For these microbes, the inside of your fridge might seem like paradise.

Mike Follows, Willenhall, West Midlands, UK