The Battle Intensifies Against Bacterial Biofilm

Bacterial colonies that form on the surface of food processing equipment can pose serious health risks to consumers, such as the listeriosis disaster that claimed 21 lives in Canada last year. These complex bacterial clusters, known as biofilms, are difficult to detect and prevent and, once they’re established, are almost impossible to remove.

A multidisciplinary team of researchers from across Canada, led by University of Guelph Prof. John Dutcher, Department of Physics, is rising to meet the challenge biofilms present to the food industry. The team is using nanotechnology-based equipment to investigate the survival of bacterial cells on surfaces, and to test possible methods for removal and prevention.

“We think about these problems in ways that differ from the traditional microbiology approach,” says Dutcher. “A physicist, chemist and mathematician come at   it from different points of view and our job is to bring all of these different ways of attacking the problem together.”

Bacterial cells colonize almost any surface where nutrients and water are available, producing biofilms with a slime coating that protects individual cells within the colonies from antimicrobial agents, such as bleach. This makes conventional methods of sterilizing surfaces within food processing equipment ineffective against biofilms.

To understand the structure of biofilms on a molecular level, Dutcher’s group uses a wide range of experimental and computational techniques, including an atomic-force microscope with a mechanism similar to that of a record player. A microscopic arm with a relatively sharp point at one end is moved over the surface of a sample and the tip shifts down or up in response to the attractive or repulsive forces between the tip and the surface. This allows the microscope to “map out” the physical characteristics of the biofilm.

Dutcher has also been experimenting with a nanoscale version of a technique called “creep relaxation,” which is typically used by engineers to test the response of building materials to prolonged stress. Researchers in Dutcher’s lab can measure the strength of the cell wall by pushing the tip of the arm into a bacterial cell for a few seconds at a set loading force, and recording how far the tip sinks in. The nanoscale creep relaxation test reveals useful information on how to target the structural integrity and resilience of biofilms.

The researchers will also be developing and testing cationic antimicrobial peptides (CAPs), compounds that can penetrate the defensive molecular barriers surrounding bacterial cells in biofilms. CAPs are expected to be one of the more successful treatments for established colonies because of their ability to penetrate and compromise the bacterial cells within biofilms. Testing the effectiveness of CAPs on established colonies is one of the researchers’ next steps.

Preventing bacterial biofilms from forming would be the ideal alternative to costly removal processes. To that end, part of this study will focus on ways to discourage colonies from growing on surfaces, such as stainless steel, by identifying and testing anti-biofilm compounds such as CAPs. As well, the researchers will be investigating the effects of changing the biofilm’s environment – such as temperature, pH, relative humidity and nutrient levels – on the survival of the bacterial cells.

“It’s a molecular approach to understanding bacterial biofilms, and that’s really what we’re all about,” says Dutcher. “Whether it’s looking at them with sophisticated techniques to see what the molecules are doing, simulating it on the computer, or putting down a layer of some surface treatment that will try to prevent the formation of biofilms – it’s all at the nanoscale level.”

Other University of Guelph professors involved in this project are Profs. Hermann Eberl, Mathematics and Statistics; Chris Gray, Physics; and Cezar Khursigara, Molecular and Cellular Biology.

Other collaborators include Profs. Lori Burrows, Department of Pathology and Molecular Medicine at McMaster University; Bob Hancock, Department of Microbiology and Immunology at the University of British Columbia; David Pink, Department of Physics at St. Francis Xavier University; Bruno Tomberli, Department of Physics and Astronomy at Brandon University; Lisbeth Truelstrup Hansen, Department of Food Science and Technology at Dalhousie University, and Gideon Wolfaardt, Department of Chemistry and Biology at Ryerson University.

Funding for this research is provided by AFMNet.

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