Breath-Based Biomarkers Identified for Tuberculosis Diagnosis

Most conventional diagnostic tests rely on sputum samples, which can be difficult to obtain and have low diagnostic sensitivity in children, HIV-infected individuals and patients with extrapulmonary TB. Therefore, the ideal diagnostic would not rely on sputum samples, and can also detect non-pulmonary TB.

Medical Scientists at the University of Toulouse III-Paul Sabatier (Toulouse, France) and their numerous colleagues included in a study eight patients between 27 and 62 years old, diagnosed with pulmonary TB by direct Ziehl-Neelsen staining and culture of sputum; 21 patients with at least three sputum samples negative for Ziehl-Neelsen staining; children (aged 6–12) were separated into two groups based on the detection or not of mycobacteria; 15 adults (aged 18–61) who presented with community-acquired pneumonia and 15 healthy adult individuals. With the goal of developing a non-sputum-based TB diagnostic, the team examined whether pulmonary TB could be detected in exhaled breath condensate (EBC) samples.

The EBCs were collected using R-tubes (Respiratory Research, Inc, Austin, TX, USA). EBCs were lyophilized and adjusted to a volume of 250 µL of LPS-free water. EBCs were spotted using the Bio-Dot SF blotting apparatus (Bio-Rad, Hercules, CA, USA) and used for Dot-blot immunoassays. The scientists then performed monosaccharide analysis and quantification by capillary electrophoresis monitored by laser-induced fluorescence (CE-LIF). MALDI-TOF analyses were performed on an AB Sciex TOF/TOF 5800 mass spectrometer using the reflectron mode (Framingham, MA, USA).

The investigators reported that that the presence of M. tuberculosis-specific lipids, lipoarabinomannan lipoglycan, and proteins in EBCs can efficiently differentiate baseline TB patients from controls. They used EBCs to track the longitudinal effects of antibiotic treatment in pediatric TB patients. In addition, M. tuberculosis lipoarabinomannan and lipids were structurally distinct in EBCs compared to ex vivo cultured bacteria, revealing specific metabolic and biochemical states of M. tuberculosis in the human lung.

The authors concluded that sampling exhaled air is non-invasive and appears to be a powerful approach that overcomes the limitations in existing assays. An EBC-based approach therefore has potentially broad application for following other pulmonary infectious agents. The study was published on December 14, 2022 in the journal Nature Communications.