Biofilms are often found associated with infections of implantable medical devices; accounting for approximately half of all nosocomial infections. Biofilms are often thought of as sessile surface-attached communities that are embedded in a protective slimy matrix. However, many bacterial pathogens also have the capacity to actively expand their biofilm communities via complex multi-cellular behaviours. We have observed that when P. aeruginosa is cultured at the interstitial surface between a coverslip and solidified nutrient media the resulting biofilm actively expands via twitching motility and is characterised by the formation of an extensive pattern of interconnected trails.
We set out to identify the factors governing pattern formation and coordinated movement during P. aeruginosa interstitial biofilm expansion. Our observations have revealed that during biofilm migration the cells at the advancing edge create furrows as they migrate across the semi-solid media The following cells are preferentially confined to these furrows, resulting in the emergence of an interconnected furrow network and the subsequent extensive large scale-patterning characteristic of these biofilms.Stigmergy is a concept which describes self-organisation processes observed in higher organisms and abiotic systems through indirect communication via persistent cues in the environment left by individuals that influence the behavior of other individuals of the group at a later point in time. Our observations indicate that self-organised pattern formation in P. aeruginosa interstitial biofilms is also a stigmergic phenomenon. To our knowledge this is the first time that stigmergy has been identified as a mechanism of self-organisation of bacterial biofilms and propose that the concept of stigmergy can be included in the repertoire of systems used by bacteria to co-ordinate complex multicellular behaviours. We are currently exploring the development of novel antimicrobial strategies aimed at controlling and inhibiting biofilm expansion in medical settings via exploiting our new understanding of biofilm expansion.