Doctoral defence: Kadri Klaos "The thin-layer agar MDR/XDR-TB Colour Test: filling the gap in diagnosing tuberculosis from a laboratory perspective“

On the 6th of February 2026 Kadri Klaos will defend her thesis "The thin-layer agar MDR/XDR-TB Colour Test: filling the gap in diagnosing tuberculosis from a laboratory perspective".

Supervisors:
Professor of pulmonology Alan Altraja, University of Tartu
Professor Francis Drobniewski, Imperial College London (United Kingdom)

Opponent:
Senior Researcher Sven Erik Sigfrid Hoffner, Karolinska Institute (Sweden)

Summary:
Tuberculosis (TB) is a treatable infectious disease caused by a slow-growing bacterium from the Mycobacterium tuberculosis complex. TB spreads only from person to person and causes approximately 10 million new cases and 1.3 million deaths globally each year. To reduce TB-related mortality and morbidity, the disease must be diagnosed as early as possible. To ensure successful treatment and assign the correct treatment regimen, it is necessary to detect TB and to determine its susceptibility to antibiotics, as TB treatment consists of at least four effective drugs.

This study evaluated the reliability, repeatability and objectivity of the MDR/XDR-TB Colour Test (CT) method used for microbiological diagnosis of TB, compared to methods recommended by the World Health Organization, both for diagnosing TB and for assessing drug susceptibility to isoniazid, rifampicin, and levofloxacin. CT is an in-house culture method, based on a thin layer of agar mixed with a colour indicator. The thin agar allows for the microscopic assessment of colony morphologies through the agar. In addition to TB detection (growing colonies obtain red colour), the CT also enables simultaneous determination of drug susceptibility from patient material, as the plate has four sectors, three of which contain the respective antibiotics.

The CT method was successfully implemented in two mycobacteriology laboratories in Estonia following introductory training. Over 1,500 CT cultures were prepared, inoculated and evaluated during the study. The results showed that the CT method consistently provided reliable results regardless of the technician or the sample. CT successfully identified drug-resistant TB strains. In the prospective phase of the study, CT enabled faster determination of drug susceptibility than the reference method.

To clarify the spread of TB in Estonia, the study compared patterns of repetitive units found in the genomes of M. tuberculosis strains. It was found that nearly 70% of the strains in Estonia share an identical pattern of repetitive sequences with another strain indicating close genetic relatedness. Additionally, the study identified risk factors for TB transmission in Estonia, such as drug resistance, alcohol abuse, being in a detention facility and HIV-positive.