Although we usually think of bacteria as a unicellular organism living alone in a liquid medium or onto a surface, it should be pointed out that 99% of the existing bacterial cells live in communities usually called biofilms. This particular behavior has deep consequences when analyzing the survival of bacteria in different situations, i.e. natural, industrial or human environments. A complete and established description of the term biofilm is: “Sessile microbial community which is characterized by irreversibly adhered cells to a substrate or interface inside an extracellular polymeric substances matrix and that exhibit an altered phenotype regarding to growth rate and genetic transcription”. Another interesting aspect about biofilms is that despite the great number of different cell types forming the biofilm and the many different surfaces they are able to develop on, the structure and organization of biofilms remains almost the same. This fact allows us to think about a common organizational structure of these bacterial communities.
Biofilms can be found almost everywhere. The ubiquitous presence of biofilms in a vast diversity of environments has several important consequences related to medicine issues (infections), industry (corrosion, yield loss) and biodeterioration of cultural patrimony. Noteworthy, the relationship between biofilms and infections should be specially pointed out due to the severity of current bacterial infections that can lead to chronic diseases which are not able to respond to antiobiotics or common antimicrobial therapies.
Bacteria have developed sophisticated cooperative mechanisms to deal with unfavorable environmental conditions. The efficient and fast spreading of microorganisms adhered to surfaces is possible due to the formation of large and ordered groups of bacteria laterally connected called “rafts”. The formation of this type of cell aggregate is a dynamic process and implies a competent colonization of surfaces because of the cooperative nature of movement. Owing that persistence of biofilms depends generally on bacterial aggregation in multicellular communities, an innovative alternative would be the development of strategies to hinder the formation of these complex structures. If the multicellular feature of biofilm is inhibited, it is possible that the host defenses could be able to manage the infection and restitute the antibiotic therapy capability.
A promising field which offers innovative alternatives to develop materials and to arrange strategies for eradication of biofilms is micro and nanotechnology. The value of applying micro and nanotechnology in biomedical sciences resides in the possibility of producing materials and designing devices capable of interacting with human organism in cellular and sub-cellular high specificity level. Our group has studied the effect of the micro and nanostructured surface features on first stages of Pseudomonas fluorescens biofilm formation. The micro and nanostructured surfaces have been fabricated by molding and replication techniques [1]. Sub-micron row and channel tuning with bacterial diameter were designed to test bacterial motility on these surfaces (MS). We have proved that bacterial spreading is severely affected by micrometric surface features. Our results showed that motility strategies (flagella orientation, elongation, aggregation in rafts, and formation of network structures and development of bacterial frontier) were affected by the presence of ordered surface submicropatterns [2]. We provide evidence that self-engineering spatial organization of bacteria is conditioned by submicropatterns tuning with bacterial size. Bacterial orientation and length are spatially restricted in this type of microstructured surface. As a consequence, motility is trickier and eventually could require more energy than movement in a non-structured surface. Importantly, the formation of large and ordered aggregates is hindered because the lateral contact required to accomplish the arrangement of bacterial “rafts” is particularly intricate in MS surfaces. Therefore, submicroengineering materials in which the characteristic dimension of surface features tune with bacterial size could be used as a valuable tool to hinder bacterial spreading rate and as a result to reduce or control biofilm formation.
After the confirmation that MS surfaces were capable of trapping cells and promoting the isolation of single cells, our research group tried to go further. So we investigated the efficacy of antibiotics in bacteria adhered to these microstructured surfaces [3]. We hypothesized that antibiotic actions against these individual cells may be maximized if the gathering of attached cells is held back. We have confirmed that the proposed strategy could be effective and that it improved the bactericidal effect of streptomycin (antibiotic). We speculate that in MS surfaces where bacterial aggregates formation was hindered, there was a greater diffusion of antibiotics into the isolated cells than in the case of non structurated surfaces where the accumulation of bacteria in aggregates resulted in greater protections against the toxic agent, reducing the antibiotic action.
This scheme concerning the modification of surface topography and the use of an antiobiotic therapy could be potentially useful in several biomedical and industrial environments. It may also be a promising alternative for environment engineering applications that require the fine tuning of material interaction with microorganisms, including controlled bacterial immobilization, antimicrobial properties and the ability to undergo surface modification.
References:
[1] O. Azzaroni, P. L. Schilardi, and R. C. Salvarezza, “Pattern Transfer Using Alkanethiolate-Protected Templates: A New Approach in Polymeric Materials Nanofabrication,” Nano Lett., vol. 1, no. 6, pp. 291–294, 2001.
[2] C. Díaz, R. C. Salvarezza, M. A. Fernández Lorenzo de Mele, and P. L. Schilardi, “Organization of Pseudomonas fluorescens on chemically different nano/microstructured surfaces.,” ACS Appl. Mater. Interfaces, vol. 2, no. 9, pp. 2530–9, Sep. 2010.
[3] C. Díaz, A. Miñán, P. L. Schilardi, and M. Fernández Lorenzo de Mele, “Synergistic antimicrobial effect against early biofilm formation: micropatterned surface plus antibiotic treatment.,” Int. J. Antimicrob. Agents, vol. 40, no. 3, pp. 221–6, Sep. 2012.