Health care workers who treat tuberculosis in developing nations diagnose the disease through an observation test. They smear a sample of sputum onto a glass slide, add a staining agent, and then count the visible bacteria under a microscope. The test is simple, cheap—and has not changed for more than 100 years.
But more than half the time, this test fails to detect early stage TB, when few of the slow-growing bacteria are present. And when there is HIV co-infection, the number of TB bacteria in the lung is often lower, thereby decreasing the sensitivity of sputum detection. Given that delayed diagnosis is detrimental for the patient and results in spread of the disease, the need for more sensitive TB tests is clear.
“The challenge is to develop a more sensitive test for this slow-growing bacteria that is still inexpensive and easy to do,” says Hai-Quan Mao, professor of materials science and engineering and faculty affiliate of the Johns Hopkins Institute for NanoBioTechnology. Working with Yukari Manabe, a Johns Hopkins TB expert, and School of Medicine Fellow and Assistant Resident, Devin O’Brien-Coon, Mao’s team has come up with a solution.
Inside the cap of a sputum collection vial, the team grafted a positively charged polymer that acts as the capturing agent. The viscous mucus sample is placed in the vial, thinned, inverted, and spun down into the cap using a manually operated, low-speed centrifugation step. Bacteria caught up in the polymer coating are then stained and counted under a microscope.
Preliminary results indicate Mao’s team is on target to invent a cost-effective and more sensitive TB test. The project grew from a student project at the Center for Bioengineering Innovation and Design and is funded by the Johns Hopkins–Coulter Translational Partnership.