Researchers from University College Cork in Ireland studied the interaction between the bacterium Pseudomonas aeruginosa, a gram negative, rod shaped bacterium which is often associated with severe burns, and the yeast Candida albicans that is the causative agent of Candidiasis, also known as "thrush",which can grow on plastic surfaces such as catheters. Both microbes are very common and although they are usually harmless to healthy individuals, they can cause disease in immunocompromised people.[1,6]
Discovery
The team discovered that molecules produced by P. aeruginosa bacteria were able to hinder the development of C. albicans 'biofilms' on silicone, when the yeast cells clump together on the
surface of the plastic. Interestingly, the interaction between the two organisms did not depend on the well-studied bacterial communication system called Quorum Sensing, indicating that a novel signalling mechanism was at play. [1]
Quorum Sensing
Quorum sensing is a commonly used type of decision making process used by decentralized groups to coordinate behaviour.In bacteria it is used to coordinate certain behaviours based on the local bacterial population density.It can occur within a single species or between species and uses signalling molecules such as oligopeptides in Gram positive bacteria and N-Acyl HomoserineLactones (AHL) in Gram-negative bacteria.[2]The discovery that the communication between P. aeruginosa and C.albicans is not mediated by quorum sensing is exciting as it will give researchers a new mechanism of bacterial communication to explore.
C.albicans
C. albicans is the most common nosocomial (hospital-acquired) fungal infection and can cause illness by adhering to and colonising plastic surfaces implanted in the body such as catheters, cardiac devices or prosthetic joints. This biofilm formation is a key aspect of C. albicans infection and is problematic as biofilms are often resistant to the antibiotics used to treat them. Dr John Morrissey, who led the team of researchers, said, "Candida albicans can cause very serious deep infections in susceptible patients and it is often found in biofilm form. It is therefore important to understand the biofilm process and how it might be controlled."[1]
Biofilms
Bacteria that adhere to implanted medical devices or damaged tissue can encase themselves in a hydrated matrix of polysaccharide and protein, and form a slimy layer known as a biofilm."A biofilm starts when a few pioneer cells use specialized chemical hooks to adhere to a surface. These pioneers help to make a target surface more attractive to subsequent cells, which
eventually mature into a complex, structured film." [3]Biofilm formation represents an incompletely understood protected mode of growth that allows cells to survive in hostile environments and also disperse to colonize new niches.Once formed,biofilms are very to eradicate and so many researchers and medical device manufacturers have tried to stop them from forming in the first place although with little success so far. [3,4,5]
Clinical Benefits and Future Work
Dr Morrissey believes his work may lead to significant clinical
benefits. "If we can exploit the same inhibitory strategy that the
bacterium P. aeruginosa uses, then we might be able to design drugs that can be used as antimicrobials to disperse yeast biofilms after they
form, or as additives onto plastics to prevent biofilm formation on
medical implants," he said. "The next steps are to identify the chemicalthat the bacterium produces and to find out what its target in the yeast is. We can then see whether this will be a feasible lead for the development of new drugs for clinical application." [1]
References
1.http://www.eurekalert.org/pub_releases/2010-05/sfgm-ffi042810.php
2.http://en.wikipedia.org/wiki/Quorum_sensing
3.Looking for Chinks in the Armor of Bacterial Biofilms,PLOS Biology (2007)
4.Antibiotic resistance of bacteria in biofilms,The Lancet,(2001)
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5.http://www.nature.com/nrmicro/journal/v2/n2/abs/nrmicro821.html,
6.http://en.wikipedia.org/wiki/Pseudomonas_aeruginosa
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