Like people, bacteria get invaded by viruses. In bacteria, the viral invaders are called bacteriophages, derived from the Greek word for bacteria-eaters, or in shortened form, “phages.” Scientists have sought to learn how the single-cell organisms survive phage infection in a bid to further understand human immunity and develop ways to combat diseases.

Now, Johns Hopkins Medicine scientists say they have shed new light on how bacteria protect themselves from certain phage invaders—by seizing genetic material from weakened, dormant phages and using it to “vaccinate” themselves to elicit an immune response.

In their experiments, the scientists say Streptococcus pyogenes bacteria (which cause strep throat) take advantage of a class of phages known as temperate phages, which can either kill cells or become dormant. The bacteria steal genetic material from temperate phages during this dormant period and form a biological “memory” of the invader that their offspring inherit as the bacteria multiply. Equipped with these memories, the new population can recognize these viruses and fight them off.