Entrevista a Bavesh Kana. África: New Study Helps Crack the Problem of Diagnosing TB in People With HIV

 To diagnose TB, one has to identify the bacteria from a sample of sputum. For this, it must be replicated by culturing them in a laboratory. Replicating bacteria are important because they aid the diagnostic process and without them, it’s difficult to diagnose TB.

Traditionally, it was thought that people who had active TB harboured bacteria that were easy to replicate through culturing. The thinking was that people with latent infection had dormant bacteria that could not replicate, which are difficult to culture.

To a great extent, this dogma wasn’t underpinned by extensive experimental evidence. This is mainly because its been difficult to model TB disease in small animals or in a laboratory.

Our research shows that these initial views were somewhat simplistic.

What did your research find?

Our research opens a new door to cracking the very difficult problem of diagnosing people who have low levels of TB bacteria, for example people who are HIV positive.

Our findings challenge the conventional thinking because we discovered that patients with active TB in reality harbour mixtures of both replicating and non-replicating organisms. This finding is significant because it will now be possible to diagnose people who previously would have gone undetected. It’s important to emphasise though, that a single TB diagnostic test will unlikely be enough to diagnose all TB disease profiles.

In our study, we explore the presence of non-replicating bacteria that are unable to grow under standard laboratory conditions. We term these as Differentially Culturable Tubercle Bacteria (DCTB).

We expect that detection of differentially culturable bacteria will now make it possible to diagnose people who have low levels of bacteria, for example older people, children and those who are HIV-positive.

How was the research done?

We approached various clinics in Soweto and identified a cohort of TB patients who had drug sensitive TB disease but had not started extensive TB treatment. Many had HIV.

Their sputum samples were subjected to the standard TB tests which includes laboratory culturing. We also applied a growth stimulating technique to the specimen to see if it could be cultured under different circumstances. We were surprised when we uncovered new populations of bacteria that were not detected using standard laboratory culturing.

We compared the results of the different tests with and without growth stimulatory factors to quantify the proportions of replicating and non-replicating bacteria in each sample. We found that using our specialist growth technique, we could more accurately predict the presence of TB disease.