Image created by Dr. Michael J. Miller
Tulane University professor of medicine Zhen Huang and his team of researchers have developed a simpler way to test for tuberculosis, commonly known as TB. Unlike traditional TB tests, Huang’s ActCRISPR-TB test can deliver accurate results in just 45 minutes.
Tuberculosis is a bacterial infection that primarily affects the respiratory system, but it can spread to other parts of the body, causing organ damage and death if left untreated. TB is spread when an infected person coughs or sneezes, releasing droplets of the bacteria into the air. TB is one of the leading causes of death worldwide, infecting nearly 10 million people every year — people with weakened immune systems are especially susceptible.
Traditional TB tests involve testing a mucus, blood or skin sample for the TB bacteria, Mycobacterium tuberculosis. Most TB tests use sputum, a combination of mucus and saliva found in the lungs. Sputum samples are cultured and analysed over the course of three consecutive days before returning a result.
While sputum testing has long been the standard for diagnosing TB, current diagnostic methods are limited by long turnaround time, accuracy and distribution challenges.
“For tuberculosis, [sputum testing] is very slow … it always takes four or even eight weeks,” Huang said. “A sputum sample is also not always available and does not always work for some cases.”
Also, many people who have TB are asymptomatic and cannot produce the mucus for tests.
“More than 75% of cases are asymptomatic,” Huang said. “It is difficult for asymptomatic patients to produce sputum, and their bacteria levels are low, so we must develop some method that can test them with high sensitivity.”
Huang’s team set out to find a solution.
Huang’s new TB test can detect small amounts of the bacteria in patients who would otherwise remain undiagnosed, using CRISPR technology to amplify the DNA of the bacteria and identify it.
To collect a saliva sample, a researcher swabs the patient’s tongue and puts it in a tube. Inside the tube, the test uses recombinase polymerase amplification. RPA is an efficient way to make DNA copies because it can be performed at a constant temperature and produces copies very quickly.
While RPA is happening, enzymes are waiting to bind to these newly made DNA strands and do so through guide RNAs. Once the enzyme reaches the TB DNA sequence, it will cut a reporter molecule, indicating that TB is present.
The positive TB result from the enzyme is reported in two different ways. The first is a fluorescent glow emitted by the reporter molecules as they are cut. The second is through a strip on the test that shows two lines indicating positive and one indicating negative.
However, diagnostic power is only half of the equation in Huang’s TB testing mechanism. This one-pot approach also eliminates the need for expensive machinery and trained medical staff.
“Anyone, with very easy training, can handle [this test],” Huang said.
Luckily, this accessibility does not come at the cost of accuracy. The ActCRISPR-TB test has shown promising diagnostic results. In clinical testing, tongue swab tests had a 74% detection rate, while traditional tests detected TB only 56% of the time.
Huang said that while his team has made progress, there is still a significant way to go before the disease is fully controlled.
“I think it will take a very long time to transfer our technologies from bench to bench … there is still a lot of work we need to do,” Huang said. “On one hand, we need to include more technology to make it easier to use. On the other hand, we need to try our best to commercialize our technology.”