A clever way to find killer bacteria

Australian researchers say they have found a way to confirm the presence of the antibiotic-resistant bacterium golden staph (Staphylococcus aureus) with quantum dot nanotechnology and a mobile phone.

Writing in the journal Sensors and Actuators B: Chemical, they describe a proof-of-concept device that uses bacterial DNA to identify the presence of golden staph in a patient sample, then determine if it will respond to frontline antibiotics.

“Our team is using synthetic biology and nanobiotechnology to address biomedical challenges,” says Anwar Sunna, from Macquarie University. “Rapid and simple ways of identifying the cause of infections and starting appropriate treatments are critical for treating patients effectively.”

Golden staph is common, and causes serious and sometimes fatal conditions such as pneumonia and heart valve infections. Of concern to the researchers – and the medical community – is a strain that does not respond to the antibiotic methicillin, known as methicillin-resistant S. aureus (MRSA).

They identified the specific bacterial strain by using a technique called convective polymerase chain reaction (cPCR). This involves a small segment of DNA being copied thousands of times, creating several samples that are suitable for testing. 

Following this, the DNA copies underwent lateral flow immunoassay – a paper-based diagnostic tool that is used to confirm either the presence or absence of a target biomarker.

The researchers – from Macquarie and the University of NSW – then used probes that were fitted with quantum dots to detect two unique genes that confirm the presence of antibiotic resistance in golden staph. 

This is where the mobile phone comes into it. A chemical that is added at the cPCR stage makes the sample fluoresce when the genes are detected by the quantum dots. The reaction can then be captured easily using the phone’s camera.

The researchers report that the new system could identify anti-biotic resistance in just 40 minutes.

While it is currently at proof-of-concept stage, they say that because of the accessibility to a camera on a smartphone, testing for the anti-biotic resistant strain could work in various environments.

“We can see this being used easily not only in hospitals, but also in GP clinics and at patient bedsides,” says lead author Vinoth Kumar Rajendran.

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