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Properties of biofilms developed on medical devices

R.A. Puiu1, G. Delete1, A.-M. Ene1, B. Nicoara1, G.M. Vlasceanu1,

A.M. Holban1,2, A.M. Grumezescu1, A. Bolocan3

'University Politehnica of Bucharest, Bucharest, Romania; 2University of Bucharest,

Bucharest, Romania; 3Carol Davila University of Medicine and Pharmacy, Bucharest,


I ntroduction

Microorganisms can grow in a free-floating form (planktonic) or as biofilms, multicellular consortia attached to certain surfaces. It is easy to understand that the majority of organisms (more than 99.9%) are able to attach and produce specific three-dimensional (3D) architectures, called biofilms (Davey and O’Toole, 2000).

Biofilms cannot be easily defined since their structure and composition differ from case to case; however, all microbial biofilms are microecosystems composed of microorganisms attached to a certain surface and immobilized in an extracellular matrix consisting of polymers of microbial origin. Along with microbial organic compounds, the matrix can contain certain blood proteins, noncellular components, such as mineralization centers (crystals), and particles resulted from corrosion (Percival et al., 2011).

Benign or pathogenic, biofilms can be found on various surfaces in different systems, due to the high number of species that are prone to form such structures. The majority of microorganisms form biofilms in aqueous media, often being present in the piping of potable water systems (Percival et al., 2011).

The incidence of biofilm formation is equivalent in both natural and man-made environments, with a higher occurrence on the superior layers of moist surfaces. However, it is not uncommon for biofilms to appear at solid/air or liquid/liquid interfaces (Percival et al., 2011).

Even though the biofilm development is not fully understood, some theories were stated regarding the advantages of the biofilm formation by microorganisms in an embedded state compared to their planktonic existence. The architectural design of the biofilm matrix ensures an increased expression of virulence genes, phenotypic changes in colony morphology, acquisition of antibiotic resistance genes by plasmid transfer, the production of high amounts of extracellular polymers (Costerton et al., 1987), enhanced access to nutrients, and closer proximity between cells facilitating mutualistic or synergistic associations and protection. Thus, once formed, biofilms are highly resistant to classic antimicrobial approaches, such as the activity of host immune mechanisms and antimicrobial drugs (Percival et al., 2011).

Biofilms and Implantable Medical Devices.

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The formation of a biofilm is a complex process, which consists of different stages: development of a surface conditioning film, microbial attachment on the surface, growth and proliferation of the micro-organisms within the surface colony, and biofilm cell detachment/dispersal (Palmer and White, 1997). Characklis et al. suggest that the detachment of biofilms could be the result of three phenomena: erosion, sloughing, and abrasion (Characklis et al., 1990).

The protection of microorganisms within a biofilm microenvironment is largely ensured through the production of a biofilm matrix made of extracellular polysaccharides, proteins, and nucleic acids (Davey and O’Toole, 2000). The fact that biofilm infections are rarely annihilated, even in individuals who have a strong adaptive immune system response, confirms the outstanding degree of resistance exhibited by biofilms (Stewart and Costerton, 2001).

The scientific world is well aware of the importance that biofilms exhibit in contracting or promoting human disease, and the number of biofilm-associated diseases seems to be increasing, due to the increasing number of implant/prosthesis-related nosocomial infections, as well as due to the discovery of new types of biofilm architectures and biofilm-forming capable species. It is crucial to understand specific characteristics of the biofilms according to the species and the type of surface they are most likely to occur.

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