How Does TB Resist Drugs?

10/09/2008

For Analise Zaunbrecher, an Emory graduate student in Microbiology and Molecular Genetics, one of the programs in the GDBBS, a typical day of research begins when she walks though four locked doors at the Centers for Disease Control and Prevention (CDC) to a wing of the building that's home to some of the most infectious diseases known to humanity.

Researching drug resistant strains of Tuberculosis

Analise is a student researcher in Dr. Thomas Shinnick's laboratory at the CDC. Her research involves looking at the mechanism of resistance to kanamycin in the bacterium that causes TB - Mycobacterium tuberculosis (to the left, in characteristic colonies; photo from the CDC.). Kanamycin is one of the second line antibiotics used to treat strains of TB that resist the first-line antibiotics, the multidrug-resistant (MDR) and the extensively drug-resistant (XDR) strains. According to the World Health Organization, about one in 20 new cases of tuberculosis in the world is resistant to first-line drugs. Patients with MDR and XDR strains of TB are typically treated using a second line of drugs, like kanamycin, but little is known about the resistance mechanisms to these antibiotics.

"It is well established that kanamycin resistance in Mycobacterium tuberculosis involves mutations in the 16S ribosomal RNA," says Analise. "But there are many reports of kanamycin resistance that cannot be attributed to this type of mutation. By analyzing a genomic library from a spontaneous kanamycin resistant mutant, we were able to map a novel mutation that confers kanamycin resistance to the promoter region of a modifying enzyme. Further investigation confirmed that this enzyme can inactivate kanamycin by acetylation, and that kanamycin resistance can be caused by over expression of this enzyme."

Understanding the mechanism of resistance is important for diagnosis and treatment.  When a patient is diagnosed with TB, it usually takes two to four weeks more to identify whether the infection is drug resistant -- at present, drug resistance is tested by growing bacterium cultures in media infused with drugs (right; photo from the CDC), which takes time.  That can mean that a crucial treatment period is wasted with ineffective medication. "If we can determine the mechanism of resistance, we can speed up the diagnostic process," says Analise. "And of course we also hope to contribute to the development of better treatments."

Working at the CDC

Analise acknowledges that her first experience working in the CDC's lab was "intimidating and scary," but she has gotten used to it. She follows the Biosafety Level 3 protocol, which includes donning scrubs, shoe booties, a hairnet and three pairs of gloves, before beginning her work in the lab. She says that there is no risk of becoming complacent with the security protocols. "You have to stay really disciplined. I don't want to challenge it. I don't want to take risk."

Working at the CDC has been a tremendous opportunity for Analise. In addition to working with some of the leading scientists in their fields, she has been impressed with the level of training she has received, and enjoys the collaborative environment. "The expertise and mentoring is excellent. You receive excellent training and input from other people. There's lots of discussion. We interpret things together."

Through her experience at Emory and the CDC, Analise feels she has come a long way in developing her own skills as a microbiologist, "I've made the transition from technician to a student and to a researcher. It's fun having your own ideas. What I am able to do has gone up in intensity and difficulty."

[Pictures note: the laboratory pictures were not taken at CDC.]

Below: Analise working using protective clothing under a flow hood -- above the work area, a fan sucks air from the room into the work area, and then through a pathogen filter before it is recirculated.