Turning the enemy against itself: SickKids-led study identifies enzymes that remove bacteria’s protective wall and enable their destruction

TORONTO – Imagine a walled city. Potential invaders are usually deterred from attacking because the strong infrastructure of that wall shields the city and its population from the outside world. Now what would happen if a wily soldier found a way to loosen one brick in the sky-high barricade? Soon, the scaffolding within the wall would give way and the structure would be pulled apart. An army could then march right into the city and launch its attack.

In a new study led by The Hospital for Sick Children (SickKids), a team of basic scientists tackled this scenario, trying to break down a wall that protects the bacteria within or prevent the wall’s construction in the first place.

In the lab, they looked at their model “city” – a bacterial biofilm, which is a grouping of bacterial cells that have embedded themselves in a wall or matrix of proteins, DNA and sugar polymers known as exopolysaccharides.  The researchers identified two enzymes that are not only used by the bacteria to construct the wall, but are also the key to loosening the brick and tearing down the wall. Armies made up of antibiotics, disinfectants and even an organism’s own immune system, which previously tried to invade the city without success, now have full access to their targets. Now that the barrier has been removed, these armies are more effectively able to attack dangerous bacteria. These same enzymes can also be used to stop the bacteria in their tracks before they could even build the wall. In essence, the researchers found two bacterial enzymes that can be turned against the bacteria, clearing a path for the attacker (antibiotics, for example) to destroy the now-vulnerable bacteria.

The North American study, which is expected to have wide-reaching clinical and industrial applications, is published in the May 20 online edition of Science Advances.

In this study, the research team characterized two enzymes that have the ability to degrade the sugar polymer component of Pseudomonas aeruginosa bacterial biofilms. Within these biofilms, the exopolysaccharides Pel and Psl are involved in the formation and maintenance of the “scaffolding” that holds up the biofilm, shielding bacteria against antimicrobials and other agents. The scientists studied two enzymes, the glycoside hydrolases PelA_h and PslG_h, which demonstrated selective targeting, the ability to degrade the exopolysaccharide component of the extracellular matrix and inhibition of biofilm formation for upwards of a 48- to 72-hour period.

“Using these enzymes, we are actually “weaponizing” the bacteria against themselves, as these are the same enzymes used by the bacteria to produce the protective polymers within the biofilm,” says the study’s principal investigator, Dr. P. Lynne Howell, Senior Scientist in the Molecular Structure & Function program at SickKids and Professor in the Department of Biochemistry at the University of Toronto. “These enzymes do not actually destroy bacteria – we see them as potential complementary therapies, which can be used to make treatment-resistant bacteria more susceptible to antibiotics or other agents, boosting the efficacy of those agents.”

Among the areas the research team is exploring as potential applications for these enzymes are the treatment of bacterial infections in the lungs of patients with cystic fibrosis, as well as the treatment of chronic wounds, such as burns or diabetic wounds, and possibly as antibacterial coatings for medical devices.

The protective properties of biofilms stand in the way of effectively destroying bacteria, contributing to problems like antibiotic resistance. Biofilms represent a significant and costly issue in health-care and industrial environments. Sixty to 85 per cent of chronic bacterial infections are biofilm related.

“Biofilms can form anywhere: on medical devices, on common surfaces, on wounds and even on our teeth. We are hoping to harness these enzymes to break down biofilms or prevent them from forming in a number of different fields,” says lead author Dr. Perrin Baker, CIHR Banting Postdoctoral Fellow at SickKids. “This methodology opens up the possibility that enzymes from other pathogenic bacteria may be exploited in a similar manner.”

While several therapies have been previously shown to prevent, and in some cases disrupt Pseudomonas biofilms, PelAh and PslGh are effective in both preventing the creation of biofilms and rapidly disrupting existing biofilms, in a matter of minutes to hours. The non-cytotoxic enzymes are able to act without penetrating the cell, thereby circumnavigating many of the defence mechanisms that the bacteria employ to resist antimicrobial therapies.

Next steps in the research will involve testing the enzymes with animal models.

“This study highlights the importance of basic science as a building block for potential new therapeutic avenues to address complex health concerns, and to stimulate changes in clinical and industrial practice,” says Howell, who also holds a Canada Research Chair in Structural Biology.

This work has been conducted in collaboration with the Industry Partnerships and Commercialization Office at SickKids.

This study was funded by the Canadian Institutes of Health Research (CIHR), Cystic Fibrosis Canada, the National Institutes of Health (NIH), the Natural Sciences and Engineering Research Council of Canada, Canada Foundation for Innovation (CFI) and SickKids Foundation.

Howell is also a Network Investigator with the Canadian Glycomics Network (GlycoNet), one of the Networks of Centres of Excellence of Canada.

This paper is an example of how SickKids is contributing to making Ontario Healthier, Wealthier and Smarter.