QUT team develops rapid staph test

A Queensland research team has developed the world's first rapid DNA test to identify methicillin resistant Staphylococcus aureus (MRSA).

In the past two decades, MRSA has become the bane of surgical wards in hospitals around the world. Not only is it resistant to methicillin, the former antibiotic of last resort, it carries a full hand of resistance genes to all common antibiotics.

The team at the Cooperative Research Centre for Diagnostics at Queensland University of Technology, led by Dr Flavia Huygens, has developed a real-time PCR test that reduces the time required to identify MRSA to as little as 6 to 8 hours, compared with 24-48 hours for the conventional technique of growing the suspect microbe on a methicillin-laced agar plate.

S. aureus, or 'golden staph' is normally a harmless resident of the human skin and upper respiratory tract, but the MRSA strain, which flourishes in the antibiotic-rich environment of hospitals, can enter surgical wounds and cause persistent, even lethal infections.

Bacteraemia, an overwhelming infection, can kill within 24 hours, the minimum time required for conventional diagnosis, so a 6-8 hour diagnosis with the new PCR test could be life-saving.

Huygens said the test first identified two gene sequences specific to S. aureus, then looked for a third sequence unique to the methicillin resistance gene.

In addition to diagnosing MRSA infections in individual patients, the new test can also help pinpoint the source of an outbreak -- for example, whether it is being spread by an asymptomatic carrier, or from patient to patient.

Real-time PCR reports a 'match' with a green fluorescent dye that intercalates with the amplified DNA and glows under UV light. The light level is measured, and analysed using special software developed by the CRC.

Huygens said her team was close to completing a similar test for vancomycin-resistant enterococci (VRE), multi-resistant microbes that inhabit the human gut and can transmit antibiotic-resistance genes for other, pathogenic bacteria.

She said the MRSA test had been developed primarily to identify the organism as soon as colonies appear on a culture plate, and the next step would be to adapt it so it could be used directly to identify MRSA directly in tissue or blood samples from patients.

Huygens said the test, and the software, could be applied to any bacterium for which diagnostic gene sequences were available. The list of completed genome projects for the world's major bacterial pathogens now exceeds 40.