Sunday, December 18, 2011

Bacteria communicate to launch an organized attack

Bacteria possess various molecules that allows for communication between them. Recently, a protein has been found which tells bacteria to get ready for battle. It helps them to launch a coordinated attack inside the organism they invaded. The scientists from the University of California who discovered the molecule proved that it also plays a role in human infections, highlighting the relevance of their findings for the clinic.

Micro-organisms do not have the capability of speech, so they need chemical signals to convey messages. There are many variants, including sending genetic messages by a specialized tube, which can, for example, induce antibiotic resistance. The newly found form of communication that turns bacteria into invaders is caused by just a single molecule, dubbed Ax21. According to the scientists, this molecule is a unique communication method, that does not fit the signalling forms that were already known.

Method of action
Ax21 is produced inside the bacterial cell, and can only act over short distances. While just being a single molecule, the signal sends a powerful message to surrounding bacteria: they change the expression of about 500 genes and significantly modify their behaviour. An example is that they multiply much faster and cause faster death of the invaded organism. It is quite remarkable that a single molecule can be so important for the capabilities of bacteria.

An additional feature of Ax21 is that it helps the bacteria form biofilms. These structures are basically homes for the bacteria, and are very hard to get rid off. Bacterial cells attach to each other and to a matrix of sturdy molecules that make the biofilm rigid. It is an example of how micro-organisms conspire together in an invasion, by clinging together and making it harder for the body to eradicate the infection.
Biofilm of S. aureus, a highly prevalent bacteria.
Intercepting communication
It appears that there is a detection mechanism that protects against bacteria that perform Ax21 signalling. Rice plants have receptors that intercept the molecule, and in response launch an powerful attack with their immune system. The receptor, called XA21, is part of a larger family of immune receptors that are needed to detect micro-organisms and other signs of infections. These receptors are so important, that their discovery lead to this year's Nobel Prize in medicine. The scientists did not state, however, whether humans possess XA21, or a similar receptor.

Because bacteria that infect humans also use Ax21, it is an important target for the clinic. If we develop drugs that inhibit the actions of this particular molecule, bacteria are much less effective in infecting our bodies, and could be eradicated much faster with conventional antibiotics. Therefore Ax21 therapy could proof to be a powerful addition in our current arsenal of weapons to battle bacteria.

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