Applying HATUA Microbiology and Molecular Methods to Investigate the Causes of Contamination in TB Culture
Mbeya Medical Research Centre
Isolation of Mycobacterium tuberculosis (M.tb) from clinical specimens is difficult due to the presence of other contaminating bacteria and fungi. The growth rate of M.tb in culture is very slow as the result rapid growers (contaminants) overgrow M.tb and compromise TB culture results. To overcome this challenge, samples are decontaminated with chemicals to eliminate contaminants still 15-30% of TB culture results are lost due to contaminations. This project will identify and characterise the types of contaminants in TB culture using microbiological and molecular approaches gained from the HATUA project.
Understanding the types of contaminants in TB culture will help clinical trialist and laboratory experts to design and establish better strategies for sample processing and overcoming contaminants. This will improve reliability of culture results which is the current measure of treatment success in routine health care and clinical trial settings.
Project Research Question: What microorganisms cause indeterminate/contaminated M. tuberculosis culture results and how can they be managed?
Project Aim: To use microbiological and molecular methods to resolve indeterminate results in TB-culture
Background: With lots of technical challenges, culture is gold standard for TB diagnosis. The main specimen type used is sputum produced by patients when they cough. In addition to Mycobacterium tuberculosis (Mtb) that cause TB, patient sputum contains many other bacteria and fungi, which when cultured grow faster than the slow growing Mtb and cause false positive results or indeterminate results where presence of Mtb cannot be determined by the current methods.
Streamlining TB culture analysis is crucial for routine TB diagnosis and treatment, and for clinical trials of novel combinations of existing or new anti-TB drugs. Sometimes indeterminate results in terms of time to positivity occurs as a result of presence of both contaminants (at high load versus lower load of M. tuberculosis). With TB-MBLA, a sensitive and specific test to Mtb, we will be able to ascertain presence and optimal load of Mtb in the MGIT instrument positive indeterminate /contaminated cultures. Secondly, we will apply the microbiological identification methods learned under HATUA to identify the bacteria or fungi underlying false positive results and design potential interventions. We will utilize the line probe assay, Hain Genotype CM to identify common species of mycobacteria which usually grows in presence or absence of M. tuberculosis.
Impact of the project: The findings of this project will clarify the definition of culture outcome which is much needed in treatment monitoring as well as defining clinical trial end-points. Identifying common causes of culture contamination will guide practical interventions towards reducing the burden of culture contamination which significantly affect clinical trial results.
Study sites: This work will be conducted by Makerere University school of biomedical sciences (MakSBS; PI, Dr. Willy Ssengooba) and at the National Institute for Medical Research (NIMR)-Mbeya Medical Research Centre (NIMR-MMRC; Co-PI, Dr. Bariki Mtafya).
MGIT culture with no contamination
MGIT culture with contamination
Blood culture plate with contamination