Throat bacteria that destroy invaders

I did a post about a week ago, talking about the relationship between the bodies natural (commensal) bacteria and the immune system. I was quite excited therefore to find a paper (reference below) which found a specific protease enzyme that is used by commensal throat bacteria to prevent harmful biofilm formation by Staphylococcus aureus, the bacteria responsible for MRSA.

The helpful bacteria in question is Staphylococcus epidermidis which lives naturally in the throat and nasal cavity of humans. When culturing these bacteria along with the Staph aureus it was found that some epidermidis cultures were capable of destroying biofilm formation, by using the protease Esp. The diagram below shows the effects of extracted Esp on colonies of Staphylococcus aureus (image from the reference):

Figures g and j show Gram stains of the colonies, the blue dye has just stained where bacteria are present. The remaining figures show scanning electron micrographs of the colonies taken at two different levels of magnification. For those interested, the scale bar for g,h,j and k is 10um and for i and l is 1um.

To double check that this protein was having an effect within the bacteria knockout mutants were made which removed the gene from Esp from the epidermidis. These bacteria were incapable of destroying Staph aureus growth. Adding a plasmid containing the Esp gene back into the bacteria restored their ability to fight off the Staph aureus which seems fairly conclusive. Furthermore this affect also works with VRSA and MRSA; Staph aureus which are resistant to antibiotics.

Below is a diagram of the effect of actual epidermidis bacteria on Staph aureus colonies (image from the reference).
These are nasal swabs taken from volunteers who had Staph aureus infections and were given the commensal epidermidis strains to try and clear them. It can be seen that the number of staph aureus is decreasing, although some bacteria are still present after five days of treatment. That might not necessarily be a bad thing as it allows the immune system to kick in with a response, and make antibodies ready for the next potential attack.

There are several exciting things that come out of this. Firstly the use of purified Esp as a defence against MRSA biofilms has the potential to be of major importance, although there may be clinical reasons why it's not such a good idea to spray proteases all over the inside of someones nose! From a less medically-useful perspective it's a wonderful example of bacterial-colony interaction. The kind of struggle for survival that happens inside your nose is occurring for bacteria everywhere; in soil, in the water, in the air, and even in humans.

From the Staph epidermidis point of view your nasal cavity is just a great place to live (warm, safe, lots of nutrients) and it's not going to give up that kind of living environment without a fight!

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Iwase, T., Uehara, Y., Shinji, H., Tajima, A., Seo, H., Takada, K., Agata, T., & Mizunoe, Y. (2010). Staphylococcus epidermidis Esp inhibits Staphylococcus aureus biofilm formation and nasal colonization Nature, 465 (7296), 346-349 DOI: 10.1038/nature09074

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