There are certainly many bacteria that do best at colder temperatures, but that doesn't mean they grow faster than other species, just that a lower temperature is their optimum. In most cases it simply means they do even worse at higher temperatures than other species. Because they are adapted for low temperatures they are less likely to be dangerous, our normal body temperature is probably lethal to them.

Any species of bacterium grows best at a particular temperature. At much above or below that temperature it grows more poorly or even may die. There are many complications in practice, such as what kind of food it is growing on, what kinds of microbes it is competing with, and so on, but the upshot is that at any temperature from several degrees below zero, to nearly boiling, a particular group of bacteria in any particular environment is likely to dominate.

Certain freak examples exceed those limiting temperatures, but never mind freak species for now. Species that are dominant at low temperatures we call cryophiles or psychrophiles.The temperatures at which a bacterium can thrive depend largely on the temperatures at which its enzymes can work at an acceptable rate without decomposing. Any bacterium that depends absolutely on at least one enzyme that cannot work outside a given temperature range cannot survive and compete outside that range.

Even within its acceptable temperature range any bacterium tends to grow faster towards the warm end of the range rather than the cooler end. If it is competing with another species of bacterium with an overlapping range of acceptable temperatures, the species nearer its own preferred temperature is likely to dominate. That temperature might actually be too warm or too cool for it, but worse for its rival. There are many special circumstances; for instance one microbe might poison another, but a difference in preferred temperature commonly will permit the more comfortable microbe to dominate its rival.

Psychrophiles in a fridge grow slowly in comparison to mesophiles, the bacteria that grow best at room temperatures, as you will discover if ever your fridge warms up for a couple of days, say because of a power failure. The mesophilic bacteria and moulds will rapidly ruin foods that would otherwise have had a shelflife of months in the fridge.

Psychrophiles rule at low temperatures, not because they work as fast as mesophiles in general, but because they work faster at low temperatures than the surviving mesophiles can.

A very rough guide for (simple) organic reactions:

The speed doubles for every 10C rise.  This obviously exagerates into the absurd at limits (for aqueous reactions) of 0C and also in gaseous phase (+100C.)

More complex molecules (because of the folding shapes of the chains eg proteins/enzymes) are more stepped in reaction speed versus temperature.

Nevertheless, for degradation chemistry (cooking) it is accurate to within +- 50%. It also applies (within narrow ranges) to organism growth.

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 Listeria monocytogenes and Yersinia enterocolitica - 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 Pseudomonas syringae 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 Carnobacterium pleistocenium, Chryseobacterium greenlandensis and Herminiimonas glaciei 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