How viruses help kill bacteria.

Viruses can harm us, one example being COVID-19. This is because viruses can not replicate or live by themselves. So they insert themselves into host cells (our cells) and use the host’s organelles and machinery to replicate. Once replicated, they burst out of the cell by cytolysis, killing the cell in the process. As a result, our cells are damaged and we begin to feel ill.

However, there are specific viruses called bacteriophages that target bacterial cells rather than human cells. ‘Bacterio’ meaning bacteria and ‘phage’ meaning engulfing or consuming. It is believed that phages could be used as a form of treatment for bacterial infections to replace antibiotics (especially considering the increase in antibiotic resistant bacteria). They were first discovered from the stool of patients that recovered from bacterial infections. These patients had bacteriophages that combated the bacteria in their body, which allowed them to survive an infection without antibiotics.

Bacteriophages infect a host bacterial cell by either one of two cycles:

  1. Lytic cycle – this cycle involves the phage genome that is inserted into the bacterium. The genome begins to synthesise proteins that break down the bacterium’s own DNA. This allows the phage to completely take over the host cell to use its organelles to replicate. Eventually the bacterium will burst, releasing the new phages to infect other cells.
  2. Lysogenic cycle – this cycle involves the phage’s DNA integrating into the bacterial DNA. This allows the phage to remain dormant in the host without being detected. The bacterium will continue to replicate its DNA along with the phages. However, this does not cause much harm to the bacterium to begin with.
This is the lytic cycle. Credit: LumenLearning
This is the lysogenic cycle. Credit: Technology Networks

What makes phages beneficial is that they target a specific species of bacteria so they will not disrupt the “good” bacteria in your gut (known as your microbiome). In contrast, antibiotics are not selective on what type of bacteria they kill.

Another benefit of phages, is that they can be used against antibiotic-resistant bacteria. Due to the increasing development of antibiotic resistance, treating bacterial infections is becoming more difficult (if you would like to read about antibiotic resistance: ). Phages have enzymes that are able to digest the biofilm that bacteria produce to protect themselves from antibiotics and, therefore, offer a solution to the increasing emergence of superbugs.

Bacteriophages were discovered in 1915, however, they have not been used widely yet. This is partly due to the emergence of antibiotics which were an easier solution to bacterial infections and lack of technology meant bacteriophages were not researched further. However, phage therapy may be used more and is even used to prevent bacterial infections on the skin of burn victims.

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