War of the Micro World

While many of us are aware that antibiotic resistance in bacteria is a growing problem, what you may not be aware of are other organisms that many scientists have considered for decades as a potential to be used against the bacteria that can cause deadly infection.

Viruses. There are approximately 10 times as many viruses as bacteria in any environment; the majority of these only infect bacteria and are referred to as ‘bacteriophage’ viruses. Bacteriophage can look like anything from a simple helical shell to a nightmarish space invader, a quick Google image search of the term ‘Virus’ quickly produces hundreds of images of bacteriophage latching on to its doomed host.

These bacteriophage inject their genetic material into the bacteria, replicate within it and then dissolve the bacteria in order to escape; thereby providing a hopeful opportunity for treating bacterial infections for humans and animals.

Studies have revealed that bacteria can develop resistance against antibiotics or bacteriophage fairly simply, through mechanisms such as producing a new antibiotic degrading enzyme or altering a receptor. This mutation, however, often comes at a cost to the bacteria. The extent of the cost depends, in part, where the resistance developed. If the resistance developed due to a mutation in its inherited DNA, there is generally a higher cost than if the resistance developed due to the bacteria gaining a plasmid (a small circular section of DNA that carries a few genes on it, and is rapidly passed between different bacterial species).

The cost to the bacteria could be due to the extra energy and nutrients required to build the enzymes, or potentially the change in the receptor may result in the bacteria not being able to bind as effectively, thereby not performing the original function efficiently. This means that when the mutated bacteria revert to growing in an environment without the antibiotics or bacteriophage, they usually get out-competed by the other bacteria that do not have the mutation.

A similar effect happens when the bacteria are put into an environment with both bacteriophage and antibiotics (although not enough antibiotics to completely kill the bacteria).

Another skill that the bacteriophage has is that they have co-evolved with bacteria throughout their evolutionary history. Consequently as the bacteria alter their receptors, the bacteriophage has become skilled at altering theirs as well so they are more compatible for infection again. This has been shown reliably by the bacteriophage in the study in order to control bacterial numbers over generations.

Although the majority of these experiments have only been done in the lab, and many of the mechanisms of resistance are still unknown; the work is promising for clinical studies that are looking at more reliable methods of treating deep bacterial infections, as the bacteriophage can reach further into infected tissue than most antibiotics.

Samuel Stokes



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