To clump or not to clump

A new technique that uses differences on the surface of bacterial cells to distinguish between different strains could lead to improved infection diagnosis for cystic fibrosis patients.

The technique, a microparticle separation technique called linear sweep three-dimensional insulator-based electrophoresis, was developed by an international team of engineers and biologists from The University of Queensland (UQ), Belgium’s Ghent University and Massachusetts Institute of Technology (MIT) in the US. The technique is much more sensitive that its predecessor, insulator-based electrophoresis, and can immobilise bacteria using low electric fields, ensuring cell viability and minimising heating.

UQ’s Australian Centre for Ecogenomics postdoctoral research fellow Dr Dana Willner said the technique would help distinguish between innocuous strains of Pseudomonas aeruginosa and those that can cause harmful infections in patients with cystic fibrosis.

“Our colleagues at MIT made a microfluidic device that’s essentially an inexpensive plastic chip etched with hourglass-shaped channels into which bacteria can be injected,” she said.

“When we applied an electric current to the chip, the bacteria reacted based on their surface properties, by clumping together or moving in different ways through the channel.

“These variations in surface properties are related to the way the bacteria behave in our bodies, and may indicate antibiotic resistance or the ability to form biofilms.”

Pseudomonas aeruginosa is a common bacterium usually harmless to humans, but it forms biofilms in the lungs of cystic fibrosis patients, causing excess production of mucus and difficulty breathing.

“Mucoid strains of Pseudomonas aeruginosa are genetically very similar to non-mucoid strains and this new technique can distinguish different strains in approximately five minutes, much faster than current diagnostic techniques which can take more than 24 hours,” Willner said.

“Although it hasn’t yet been tested with patient samples, we believe it can be developed into a portable, disposable system for clinical use to rapidly detect the presence of mucoid strains which can indicate more severe diseases.

“Rapid detection could lead to quicker diagnosis and more prompt treatment for patients.”

The research was initiated by Professor Korneel Rabaey, now at Ghent University, while he was a Senior Research Fellow at UQ’s Advanced Water Management Centre.

He said the sensitivity of the technique allowed for a range of applications.

“Further variations will allow us to look inside cells, and, for example, find out how much oil is inside an algal cell for biofuel production,” Professor Rabaey said.

Australian Centre for Ecogenomics Director Professor Philip Hugenholtz said the technique would be useful for understanding the connection between the surface properties of a bacterium and the genes it expressed.

“This technique is a powerful new tool for rapidly isolating and studying bacterial strains with subtly different surface properties that we can then sequence to help pinpoint the genes responsible," he said.

The research was funded by a collaborative grant between MIT and UQ and conducted at UQ’s Advanced Water Management Centre, the Australian Centre for Ecogenomics and MIT’s Mechanical Engineering Laboratory for Energy and Microsystems Innovation.

It has been published in the journal PLoS ONE.