Biofilms – lifestyles of the fixed and resilient!

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The paper in npj Biofilms and Microbiomes is here:

It may surprise non-microbiologists, and perhaps even some microbiologists, to learn that most bacteria do not normally live in nutrient broth within the glass confines of a test-tube or flask.  Most bacteria do not exist as planktonic cultures, with ready access to all essential nutrients and at their optimum growth temperature, pH and oxygen levels.  And yet, this is how most bacteria are grown when we are testing for resistance to antibiotics or other antimicrobial agents.  The bacteria that inhabit the real world are tough survivors, who have to learn to attach to solid materials, to compete with their neighbours, and form alliances with potential friends and enemies.  Multi-species biofilms represent the ‘real’ word but of course it is very difficult to replicate these complex communities in the laboratory, something which is required for multiple testing, and the kind of reproducibility required to set minimum inhibitory concentrations (MIC) for antimicrobials.

But if biofilms are where bacteria live (in catheters, on equipment surfaces, on body surfaces such as teeth and skin, and in the gut), how can we model the impact of antimicrobial treatments.  How can we gauge the appropriate exposure in terms of concentration and time.  It has been estimated that perhaps as much as 100-1000x the ‘planktonic’ MIC is required to eliminate bacteria in biofilms.  In clinical settings, should we focus on preventing the formation of biofilms, or do we need to find ways to destroy pre-formed biofilms?

We have worked for many years now with bacteriocins, small antimicrobial peptides with exquisite antimicrobial activity which can be up to 1000 times more active than classical antibiotics.  The lantibiotics are a specialised subclass of bacteriocins with elaborate post-translational modifications like nisin, which has been shown to penetrate biofilms to great effect.  We thought it was timely to review the significant literature surrounding lantibiotics and other bacteriocins and their ability to prevent and destroy biofilms in a variety of settings. We also speculate on the possibility of deploying living strains producing bacteriocins into environments likely to support biofilms, encouraging the bacterium to infiltrate and disrupt stable biofilm communities. 

As with all things, bacteriocins are not the complete answer to biofilms but they may be a part of a wider solution in particular clinical settings, including indwelling devices, dental caries and perhaps in the gut.

Colin Hill

Professor of Microbiology, University College Cork