Scientists have devised a low-cost imaging technique that can diagnose live tuberculosis bacteria in an hour, and help monitor the efficacy of treatments. Many TB strains have evolved defences against standard treatments, therefore speedy diagnostics are needed, said Jianghong Rao, a professor at Stanford University in the US. 

Current methods can take up to two months to complete, a stretch during which an infected individual could spread TB broadly, even if they do not know it, he said. The new method, described in the journal Science Translational Medicine, is cheaper and easier to carry out, ideally enabling health care providers in poorer communities to adopt the technology. Currently, to diagnose TB clinicians need to collect a spit sample, cultivate it in the lab, and wait for the bacteria to grow to detectable level.

It also requires specialised facilities, which are missing in many hospitals worldwide.In still-developing countries where TB is most prominent, it is hard to maintain those kinds of intensive facilities, and it can be expensive," said Rao.The new imaging technique uses run-of-the-mill fluorescence microscopes that nearly all hospitals have and no special training required, he said.

All that is needed is a sample of the patient's "sputum," or a spit sample, that can be prepared and put under the microscope for analysis.The tactic harnesses a newly created two-piece fluorescent probe, which Rao likens to a lamp. The probe is combined with the spit sample and gets activated, or "switched on," when it comes in contact with TB bacteria.

One part of the probe is responsible for detecting live TB, thus creating the telltale glow, and the second part, a molecule that binds specifically to the TB microbe, localises the glow to the bacterium.The concentrated fluorescence allows scientists to not only see the rod-shaped bacteria themselves, but also to track their distribution in infected host cells."For cases of drug-susceptible TB, the treatment success rates are at least 85 per cent, but the rate of success is only 54 per cent for multidrug-resistant TB, which requires longer treatments and more expensive, more toxic drugs," Rao said.

The fluorescent probe, Rao said, can help determine the appropriate drug by literally showing which bacteria are still alive in the patient sample.Those that are alive glow green; those that are not (or are a different species of bacteria) appear dark.Outside of the clinic, Rao said that the technique could help scientists developing new TB drugs figure out which drugs work best for each particular strain.