"Integrons are like decks of cards in bacteria except that instead of cards, they are decks of resistance genes. They are all lined up in one cohesive stretch of DNA and they are linked to each other. Integrons are one way that bacteria can become resistant to lots of antibiotics all at once. The problem with integrons (for bacteria) is that mostly bacteria can only play the first card in the deck meaning that they can only efficiently express the first gene in the integron. If the bacteria are exposed to an antibiotic that they have a resistance gene for, but that resistance gene isn't the first one in the integron, it won't do them much good, because they can't express it. However, just like cards in a deck, the bacteria can shuffle the resistance genes in an integron and reorganize the order they are in. This enables them to change which one is first."