Do bacteria get the sniffles? Bacterial immunity discovered

Infection of a bacterium

Phages attached to the side of a bacterium. Source: Dr Graham Colm (

OK so first, let’s talk about the fact that like us, bacteria can get “sick”. Bacteria can be infected by a specific type of viruses called phage. By depositing its genes inside the bacterium, a phage can hijack the bacterium’s metabolism to produce new phages, which ultimately destroy the bacterium. Over the last ten years, researchers have shown that amazingly bacteria can also fight off infection with a bacterial equivalent to the immune system (termed CRISPR-cas system).

To fight off infection, bacteria use the phage’s DNA by cutting it up and inserting the pieces into their own chromosome. During the next phage infection, the bacterium can compare the phage DNA to this library of previous infections and if it matches, use it to fight the phage. When this “immunised” bacterium divides, it transmits the library to it’s daughters, who will in turn replicate, thereby producing a population of bacteria resistant to that particular set of phages.

However, if the bacterium is killed by the infection, how could its daughter cells inherit its library? In the July issue of Nature communications, Hynes et al. have addressed this issue by demonstrating that the bacteria that carry the library have most likely been infected by non-functional or attenuated phages. This is quite similar to the way humans are protected from infection by inoculation of attenuated viruses, such as the flu or measles vaccines. It is therefore reasonable to say that in order to prevent disease, bacteria seem to be, like us, vaccinated.

Now apart from basking at the everlasting wonder that is biology, you might ask, why is this important? For one, scientists have now harnessed the CRISPR-cas system as a ground-breaking tool for genetic engineering which can be used in many areas of biology research, such as cancer research, microbiology, immunology etc.. But most importantly, understanding bacterial immunity might help us develop enhanced or alternative treatments against bacterial infection, in a world where antibiotic resistance is an ever-growing problem.

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Scientist studying the ins and outs of the interactions between the human host and the pathogens that infect it. I obtained my PhD in 2012 in the University of Bordeaux, France and I am currently working at Imperial College London, UK. I aim to share my passion for science by making it simple and approachable, so please feel free to post questions you'd like answered on

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