Tuesday 18th November 11:01 am
‘Good guy’ virus kills bacteria
Tuesday 18th November 2014 11:01 am
There have been tantalising reports for thousands of years that the waters of certain holy rivers (such as the Ganges and Yumuna rivers in India) could cure infectious diseases such as leprosy, cholera, the plague and dysentry. This knowledge is giving us a new way to kill bad bacteria.
Antibiotics have been used for three quarters of a century to treat bacterial infections. Evolution is real. And so bacteria have evolved resistance to the antibiotics we use to kill them.
We then invented new antibiotics, in response the bacteria evolved again — and the cycle repeats. The problem is that we are already running out of new antibiotics, but bacteria won’t run out of evolution.
It turns out that there is a living creature that kills bacteria — a virus called a bacteriophage. The name literally means ‘bacteria eater’.
In 1896, while in India, Ernest Hanbury Hankin investigated the supposed healing powers of the holy rivers. He discovered ‘something’ that could kill the cholera bacterium. This mysterious agent was smaller than bacteria — about one hundredth the size. This was our first scientific inkling of the existence of the bacteriophage.
The bacteriophage was discovered independently by the British bacteriologist Frederick Twort in 1915, and the French-Canadian microbiologist Felix d’Herelle in 1917. It turns out that bacteriophages are the most numerous life forms on Earth – about 100 million in each gram of dirt, or each millilitre of water.
In the 1920s, bacteriophages were used to treat bacterial infections in both the United States, and in Georgia in the Soviet Union. Nothing else worked – antibiotics had not yet been invented.
Bacteriophages were developed and used in Georgia until the present day. But in the West they were abandoned immediately after the introduction of antibiotics. There were several reasons for this.
Antibiotics were cheap, easy to make, store and prescribe. On the other hand, bacteriophages had to be individually blended, on demand. Furthermore, antibiotics could attack a whole range of different bacteria, while bacteriophages would work only against very specific bacteria. If you wanted to kill a different bacterium, you needed to use a different bacteriophage.
Also, when the Soviet’s high quality research was eventually carried out, nobody in the West translated it into English. So very few people in the West had even heard of bacteriophages.
We currently know of some 19 different families. Ten of these families will infect bacteria. Your typical bacteriophage virus looks a bit like a moon lander – a tall skinny body on top of a bunch of spindly legs.
The bacteriophage lands on a bacterium, legs down. The legs then bend and the body of the bacteriophage makes contact with the much larger body of the bacterium. The tail of the bacteriophage then penetrates into the bacterium and injects some of its genetic DNA. The bacteriophage DNA then forces the host bacterium to start making more bacteriophages — sometimes within 15 minutes.
Bacteriophage viruses are so potent that they kill about half the bacteria on Earth every two days.
Bacteriophages have been accepted in the West very slowly. It took until 2006 before the American Food and Drug Administration would approve bacteriophage products. They are now being used as a food additive to kill both theE. Coli and Listeria bacteria, and also to treat ear infections in dogs.
Each type of bacteriophage has evolved to attack only a very limited range of bacteria. But this turns out to have advantages.
If you take an antibiotic to treat an ear infection, it will also accidentally kill many of the essential and friendly bacteria that live in your gut. Bacteriophage therapy will leave these friendly bacteria alone. Bacteriophages are more like a guided missile than a nuclear bomb.
Another advantage is that when the bacteria evolve to be resistant to one type of bacteriophage, there is always another slightly different bacteriophage just around the corner. Nature has a virtually inexhaustible supply of them. So you just try another bacteriophage to treat the patient.
Indeed, we can now use modern molecular biology to quickly match up a bacteriophage with your intended target.
So here is a good guy virus, unlike viruses such as SARS, MERS and Ebola.
This blog first appeared on Dr Karl's Great Moments in Science
© 2017 Karl S. Kruszelnicki Pty Ltd