Image: A Pf bacteriophage invades a mammalian cell. Credit: Dr.Paul L. Bollyky, et al.
For the first time ever, a bacteria has been found to weaponize its own virus to attack humans. A common bacteria called Pseudomonas aeruginosa produces a virus that makes the bacteria itself significantly more pathogenic.
The virus in question is called a bacteriophage – or phage for short – and belongs to a family of viruses that are thought to only be capable of infecting bacteria. P. aeruginosa, however, uses its phage to cause our bodies to react to a virus while ignoring the bacteria that produces it. In a Trojan horse strategy, this allows the bacteria to enter our cells and in the process, evades many common antibiotic therapies.
The World Health Organisation has labeled P. aeruginosa a “critical priority” pathogen; one that poses the greatest threat to human health. P. aeruginosa has been growing increasingly drug-resistant and accounts for a sizeable portion of infections involving ulcers, bedsores and burn wounds.
Bacteria-eating cells in our bodies called phagocytes are trained to target and destroy bacteria by essentially eating them up. When a phagocyte encounters a virus, however, its reaction is to prevent the virus from getting inside the phagocyte, as doing so would lead to a viral infection. When phagocytes encounter P. aeruginosa’s bacteriophage, called Pf, they recognize its viral proteins and treat the entire bacterial cell as though it was a virus-infected human cell. The effect, says study lead author Dr. Paul Bollyky, is like somebody pulling the fire alarm when they should have called the police. “If 20 fire engines pull up to the scene of the crime, it makes it easier for the thief to get away.”
These findings are significant, in that they change how we will have to view phages in the future. Although the idea that phages could be used to infect mammalian cells had been first proposed by Dr. Carl Merril in the 1970’s, it was met with derision and largely forgotten. The new study hammers home the fact that this process does, in fact, occur and must be taken seriously.
Fortunately, Dr. Bollyky’s team developed a vaccine against Pf, that successfully reduced the incidence of wounds infected with P. aeruginosa by half. Encouragingly, their vaccine may prove useful against other pathogenic bacteria as well, as several other species can also carry Pf and end to co-infect wounds colonized by P. aeruginosa.
The study was published in the journal Science on 29 March.