Study Design and Setting
We conducted a prospective cohort study, from February 2016 to August 2020, enrolling consecutively newly diagnosed adults with sputum smear-positive (confirmed later to be TB culture positive) from local TB diagnostic and treatment centers in Bamako, Mali. Bamako, the capital city, has a population of approximately three million people, about 14% of the population of Mali, living in six urban districts, with each district having a health referral center, where TB diagnostic and treatment services are available. In 2019 alone, more than one third of the total TB patients in Mali (6,902 patients) were diagnosed and managed in Bamako.
The study population included a group of patients and healthy individuals matched by age and gender. The TB-infected participants had four study visits for clinical investigation and sample collection as follows: before TB treatment starts, two months and six months during anti-tuberculosis therapy, and then nine months after treatment completion. However, Healthy individuals’ samples were collected at recruitment and six months after inclusion.
Study Subjects and Samples Processing
Samples collected include sputum, plasma, and stool from each participant. Participants of 18 years old and more, who were newly diagnosed microscopically with pulmonary tuberculosis (TB Group) and healthy control volunteers, with no TB disease or latent TB as confirmed by the QuantiFERON-TB Gold assay (QFT-Plus; Qiagen, Hilden, Germany) as the control group. All the participants were confirmed HIV seronegative and without prior anti-tuberculosis therapy or antibiotics in the past 4 weeks. A written and signed informed consent form was obtained from each participant before being enrolled. The confirmed cases of the newly diagnosed TB patients were followed before and after starting a first-line anti-tuberculosis treatment regimen comprising two months of isoniazid (H), rifampin (R), pyrazinamide (Z), ethambutol (E), followed by four months of rifampin (R), and isoniazid (H) (2HRZE/4RH).
Shotgun metagenomic sequencing was performed at the University of Illinois at Chicago Research Genome Core Laboratory using the laboratory standards procedure with Illumina. Levels of validated plasma markers of gut microbiota-produced metabolites (metabolomics), including SCFAs, were evaluated using high-performance liquid chromatography (HPLC) by Metabolon. Plasma samples collected from TB patients were tested with a Becton Dickinson (BD) LSR II flow cytometer to measure the level of cytokines.
Mycobacterial identifications
Early morning sputum specimens collected from presumptive TB patients were tested for TB using the standard N-acetyl-L-cysteine/4% sodium hydroxide solution for sputum digestion and decontamination, thereafter, the sample was concentrated by high-speed centrifugation. The pellets were used to inoculate liquid medium (Mycobacterium Growth Incubator Tube (MGIT™) [BD, Sparks, MD, USA], and solid medium (Middlebrook 7H11 agar and selective 7H11 agar) to isolate pure mycobacteria colonies, as previously described [17]. The concentrated specimen also served simultaneously to prepare an auramine-rhodamine smear for fluorescent acid-fast microscopy visualization (BBL™, BD, Sparks, MD, USA). The speciation of the isolated mycobacteria was based on the observation of colonial morphology from culture media and the use of Gen-Probe TB molecular assay (AccuProbe®, San Diego, CA, USA) [18].
Cytokine Measurements
Cytokines’ levels over time were determined to evaluate the immune evolution of the disease from pre-treatment to post-treatment status. To achieve this, the Human Th1/Th2/Th17 kit was used according to the manufacturer’s instructions (BD Biosciences, Torreyana Rd, San Diego, USA). The BD Cytometry Bead Array (CBA) was used to evaluate the following cytokines levels: Interleukin-2 (IL2), Interleukin-4 (IL4), Interleukin-6 (IL6), Interleukin-10 (IL10), Tumor Necrosis Factor (TNF), Interferon-gamma (IFN-γ) and Interleukin-17 alpha (IL17A) from plasma samples.
Briefly, before running the assays, samples were removed from -80°C to the cold room (4-8°C) for thawing. Samples and standards were then prepared and measured following the manufacturer’s instructions, by using an LSR II flow cytometer at the University Clinical Research Center (UCRC) immunology core facility laboratory. Analysis was then performed by FCAP Array TM software version 3.0.1. The detection limits for each cytokines measured were as follow: IL-2 (2.6 pg/mL), IL-4 (4.9 pg/mL), IL-6 (2.4 pg/mL), IL-10 (4.5 pg/mL), TNF (3.8 pg/mL), IFN-γ (3.7 pg/mL) and IL-17A (18.9 pg/mL).
DNA Extraction from stool samples
DNA was extracted from stool samples using the QIAmp DNA Stool Mini Kit (Qiagen, Hilden, Germany). Frozen stool samples were placed and tawed on ice before the extraction starts. The stool samples were first weighed (180-220 mg of thawed stool) then extraction was performed according to the manufacturer’s instructions. The extracted DNA was then measured using the Nanodrop Onec (Thermofisher Scientific, Verona Rd, Madison, USA) to assess the DNA concentration and its purity, before sending for sequencing.
Shotgun metagenomics of the gut microbiome and bioinformatics analysis
DNA extracted from stool samples was sequenced at the University of Illinois at Chicago (UIC) Research Genome Core Laboratory using Illumina HiSeq, and the sequences were analyzed by Dr. Anthony Fodor’s team at the University of North Carolina at Charlotte. The host contamination of shotgun metagenomics reads was removed using Kneaddata. The taxonomic composition of the microbiome was characterized using Kraken2, and the functional pathways (stratified pathways and unstratified pathways) were characterized using HUMAnN2 following the developers’ instructions. The R software was used for downstream statistical analysis of taxonomic composition and pathway abundances. The PCoA ordination was calculated with function ‘capscale’ in the R package ‘vegan’ using Bray-Curtis dissimilarity. The Shannon diversity was calculated with function ‘diversity’ in the same package. The linear mixed-effects models were performed with function ‘lme’ in R package ‘nlme’, with healthy/TB group, timepoints, and their interaction as the main effects and subject ID as the random effects. P values were adjusted using the Benjamini-Hochberg method to correct for multiple hypotheses testing. False Discovery Rate (FDR) <0.05 was considered as statistically significant.
Metabolomics Analysis of plasma samples
Metabolomic analysis was performed on the plasma samples collected from TB infected individuals (including samples before treatment, at 6-month treatment, and at 9-month after treatment completion). Each sample received was accessioned to the Metabolon Laboratory Information Management System (LIMS) and was assigned by the LIMS a unique identifier that was associated with the source identifier only. This identifier was used to track all sample handling, tasks, results, etc. The samples (and all derived aliquots) were tracked by the LIMS system. All portions of any sample were automatically assigned their unique identifiers by the LIMS when a new task was created; the relationship of these samples was also tracked.
Plasma samples were prepared using the automated MicroLab STAR® system from Hamilton Company. Several recovery standards were added before the first step in the extraction process for QC purposes. To remove protein, dissociate small molecules bound to protein or trapped in the precipitated protein matrix, and recover chemically diverse metabolites, proteins were precipitated with methanol under vigorous shaking for 2 min (Glen Mills GenoGrinder 2000) followed by centrifugation. The resulting extract was divided into five fractions: two for analysis by two separate reverse phases (RP)/UPLC-MS/MS methods with positive ion mode electrospray ionization (ESI), one for analysis by RP/UPLC-MS/MS with negative ion mode ESI, one for analysis by HILIC/UPLC-MS/MS with negative ion mode ESI, and one sample was reserved for backup. Samples were placed briefly on a TurboVap® (Zymark) to remove the organic solvent. The sample extracts were stored overnight under nitrogen before preparation for analysis. The metabolomics results were analyzed using R software. GraphPad prism version 8.0.1, was used for patients’ social characteristics analyses and cytokines measurement analysis.
Availability of data and materials
Not available.