Microbiology

Biofilms : More than Superficially Harmful

Biofilms consist of diverse microorganisms physically linked together–and to the underlying surface–by substances they secrete. French teams have outlined two different approaches for eliminating these layers and the accompanying threat of potentially dangerous contamination.

Some biofilms, such as those covering the intestine, are benign or even beneficial, but many others can cause major problems. This is particularly true of biofilms that form on surfaces in food-processing plants and on medical equipment (especially catheters and other indwelling devices), which can be sources of infection and contamination. Indeed, it has been suggested that up to 60% of hospital-acquired infections are due to biofilms. Prevention is better than cure, and this adage has become even more pertinent with the emergence of antibiotic-resistant bacteria, including some strains found in biofilms. Furthermore, bacteria that are part of a biofilm structure often demonstrate increased resistance to antibiotics and the immune system's defensive efforts compared to their planktonic counterparts.

Preventing biofilm formation, therefore, is an important goal for both the agrofood industry and the healthcare sector. Two groups of researchers in France have been tackling this problem: In both cases, the aim is to prevent the adhesion of microorganisms and thereby inhibit biofilm formation. However, the approaches used are rather different.

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© CNRS Photothèque

An image from an electron scanning microscope of a Staphylococcus aureus biofilm on a vascular prosthesis.

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Many of the major surfaces in agrofood processing plants are made of stainless steel. “Certain yeasts can bind tightly to steel,” points out Muriel Mercier-Bonin from INRA's Biotechnology-Bioprocesses Lab.¹ “However, if the steel is covered with a thin layer containing silver nanoparticles, yeasts bind more weakly, and can be cleaned off much more easily.” Together with scientists in Toulouse,² the team has developed a technique for coating the steel surface with a polymer matrix containing silver nanoparticles.³ The process involves argon-organosilicon mixtures submitted to electrical discharges (ions + electrons) which lead to energetic electron-molecule collisions, and then to fragmentation of the organosilicon. The resulting active species form the polymer on the steel surface. Simultaneously, argon ions are accelerated by a strong electric field created in the vicinity of a silver electrode. They promote an intensive electrode bombardment, causing silver atoms to be ejected and subsequently be incorporated into the polymer as anti-microbial nanoparticles.

In contrast to this physico-chemical approach, the team led by Jean-Marc Ghigo⁴ has rooted their research in biochemistry and bacteriology. In a recent paper,⁵ they described the potentially valuable properties of a complex sugar, the so-called group II capsular polysaccharide. This polymer is produced by various E. coli strains and is secreted so as to encase the bacterial surface, forming a “capsule.” The strains of E. coli producing these biofilm inhibitors are responsible for urogenital tract infections. It seems likely that group II capsular polysaccharides confer a competitive advantage and prevent these bacteria from becoming trapped in biofilms themselves, thereby favoring their circulation through the body after ingestion, eventually reaching the urogenital tract. These secreted group II capsular polysaccharides are able to prevent many bacterial species, including pathogenic E. coli, Pseudomonas aeruginosa, and Staphylococcus aureus, from attaching to glass and PVC, thereby inhibiting biofilm formation. Their anti-adhesion properties could thus be used to prevent biofilm formation on items as diverse as contact lenses, prostheses, food processing surfaces, and sewers.

These developments have the potential to lead to exciting applications for helping prevent infection and contamination in various contexts, by protecting surfaces from biofilm formation.

Alex Edelman