Study Indicates that Bacteria Adhere Poorly to Soft Surfaces

Originally Published MPMN September 2008

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Study Indicates that Bacteria Adhere Poorly to Soft Surfaces

Daniel Grace

Contrary to assumption, bacteria exhibit poor adhesion to soft surfaces and good adhesion to hard surfaces, according to a new study conducted by researchers at the Massachusetts Institute of Technology (MIT; Cambridge, MA; www.mit.edu). This finding could influence future efforts by medical device OEMs to combat biofilms—bacterial clusters that often form on catheters, among other medical devices.

Bacterial surface attachment is the first step toward the formation of biofilms, which are a major cause of hospital-acquired infections. Biofilms are sticky and resistant to traditional antibiotics; often the only certain way to remove them is by physical scraping, which is not an option with medical implants.

In an attempt to learn more about bacterial adhesion, the research team—materials science and engineering specialists—incubated E. Coli and Staphylococcus bacteria on polymer films with various precisely controlled stiffnesses. Though the two types of bacteria are significantly different in terms of structure, both demonstrated a similar reaction to surface mechanics in the study. The number of bacteria that adhered to a stiff surface was orders of magnitude greater than the number that adhered to a soft surface.

“In the past, researchers have investigated several different variables in attempting to learn more about what causes bacteria to stick [to surfaces],” says Jenny Lichter, an MIT graduate student and a primary member of the research team. “But this is the first time anyone has controlled for mechanical stiffness.”

Specialized tools, such as atomic force microscopy, have been used in the recent past for studying how mechanical force affects cells. Until the MIT study, however, bacterial cells had never been approached as an appropriate subject for enlisting such tools. It was assumed that bacterial cells, relatively simple compared with animal cells, didn’t have the internal structures necessary to respond to mechanical stimuli. The MIT researchers spent two years experimenting and controlling for all regulators of adhesion in order to ensure that mechanical effects were being observed and not some other factor.

The soft polymer films used in the study were created by dipping an object or device into water-based solutions of biocompatible polymers, a method that could potentially be used to manufacture antibacterial coatings for medical devices. In addition, the soft films could incorporate antibacterial coating approaches introduced by other researchers, such as water-repelling designs, bacteria-bursting capabilities, and embedded silver nanoparticles.

The study’s findings could also be used to benefit future research. Since bacteria are difficult to study because they can’t be cultured in laboratories using traditional methods, stiff coatings could be used to promote bacterial growth. It’s unclear why bacteria adhere better to stiffer surfaces, but upcoming efforts by the researchers could include attempts to answer that question, according to Lichter.

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