A research team at Imperial College London (ICL) has developed a quick, cheap method to detect the presence of Pseudomonas aeruginosa in sputum samples collected from patients with cystic fibrosis (CF).
Using small engineered DNA circuits called cell-free biosensors, the method reveals molecules specifically produced by P. aeruginosa. When the biosensor detects these molecules, it retrieves a fluorescent signal that can be easily identified.
The ICL team’s study, “A Cell-Free Biosensor for Detecting Quorum Sensing Molecules in P. Aeruginosa-Infected Respiratory Samples,” appeared in the journal ACS Synthetic Biology.
“The driving force behind this research is to show that these tools work and could be used to detect particular diagnostic markers associated with infection,” the study’s lead author, Paul Freemont, co-founder and co-director of ICL’s Centre for Synthetic Biology and Innovation, said in a news release. “By applying an engineering approach to biology, these systems could be altered to sense for any microbe we choose. The possibilities for public health and cost-savings for health systems could be considerable.”
Initially, biosensors needed to be inserted into living cells so they can act as a closed circuit. When in the presence of the right signal, the circuit would be turned “on” and a fluorescent protein would make the cell become colored. If the required signal was not present, then the circuit would remain “off” and no fluorescent color would appear.
The new method is innovative because it doesn’t require living cells. It is instead a “cell-free” form of sensor that works in a free-floating solution.
The ICL team specifically designed its sensor to respond to the presence of acyl homoserine lactones (AHLs) that P. aeruginosa produce to communicate with each other.
To test the biosensor’s detection capacity, the team collected sputum samples from CF patients that were positive or negative for P. aeruginosa. After leaving the biosensor with the samples for four hours, researchers confirmed that it had the capacity to recognize the presence of the bacterial signature. Moreover, cell-free biosensors showed detected bacteria presence with the same accuracy as available diagnostic tests.
This new method could potentially become a rapid diagnostic test costing just a fraction of the price of existing tests. However, some limits must still be overcome, such as the time required for sample preparation or the potential for cross-contamination.
“At the moment, we only have opportunities to detect infection when patients come to clinics, perhaps every two to three months,” said the study’s co-author, Jane Davies, an honorary consultant pediatrician at the Royal Brompton Hospital. “A point-of-care test could transform the way in which we monitor patients, allowing us to treat early and personalize therapies.”
The group is exploring ways to further develop the biosensor to make it more versatile and transform it into a more ready-to-use format.
“Now we have shown these types of biosensors can be used with clinical samples. The next step is to refine our approach,” said Loren Cameron, also an author of the study. “We hope that in future, tools like this could be used to help test for the presence or severity of bacterial infections.”