Virulence of Mycobacterium tuberculosis Clinical Isolates Is Associated With Sputum Pre-treatment Bacterial Load, Lineage, Survival in Macrophages, and Cytokine Response

Abstract

It is uncertain whether differences in Mycobacterium tuberculosis (Mtb) virulence defined in vitro influence clinical tuberculosis pathogenesis, transmission, and mortality. We primarily used a macrophage lysis model to characterize the virulence of Mtb isolates collected from 153 Vietnamese adults with pulmonary tuberculosis. The virulence phenotypes were then investigated for their relationship with sputum bacterial load, bacterial lineages, bacterial growth, and cytokine responses in macrophages. Over 6 days of infection, 34 isolates (22.2%) showed low virulence (< 5% macrophages lysed), 46 isolates (30.1%) showed high virulence (≥90% lysis of macrophages), and 73 isolates (47.7%) were of intermediate virulence (5–90% macrophages lysed). Highly virulent isolates were associated with an increased bacterial load in patients' sputum before anti-tuberculosis therapy (P = 0.02). Isolate-dependent virulence phenotype was consistent in both THP-1 and human monocyte-derived macrophages. High virulence isolates survived better and replicated in macrophages one hundred fold faster than those with low virulence. Macrophages infected with high virulence isolates produced lower concentrations of TNF-α and IL-6 (P = 0.002 and 0.0005, respectively), but higher concentration of IL-1β (P = 5.1 × 10−5) compared to those infected with low virulence isolates. High virulence was strongly associated with East Asian/Beijing lineage [P = 0.002, Odd ratio (OR) = 4.32, 95% confident intervals (CI) 1.68–11.13]. The association between virulence phenotypes, bacterial growth, and proinflammatory cytokines in macrophages suggest the suppression of certain proinflammatory cytokines (TNF-α and IL-6) but not IL-1β allows better intracellular survival of highly virulent Mtb. This could result in rapid macrophage lysis and higher bacterial load in sputum of patients infected with high virulence isolates, which may contribute to the pathogenesis and success of the Beijing lineage.

Mycobacterium tuberculosis Rv0341 Promotes Mycobacterium Survival in In Vitro Hostile Environments and within Macrophages and Induces Cytokines Expression

“…However, prolonged IL-1β expression could lead to serious tissue injury [ 39 , 40 ]. Virulent Mtb strain can induce a significant amount of IL-1β compared with less virulent strains [ 41 ]. Mtb early secretory antigenic target-6KDa (ESAT-6) can induce IL-1β from the peripheral blood macrophages obtained from latent TB patients compared with the cells from active TB patients [ 42 ].…”

“…In the present study, we found that Ms_Rv0341 stimulated a more significant expression of TNF-α than Ms_Vec. Elevated levels of TNF-α were linked with hyper-virulent Mtb strains and increased number of bacilli in the patient’s sputum [ 41 ].…”

Rv3737 Is Required for Mycobacterium Tuberculosis Growth in Vitro and in Vivo and Correlates With Bacterial Load and Disease Severity in Human Tuberculosis

“…At 24 h and 72 h after infection, both extracellular bacteria released from macrophage lysed in supernatant and intracellular bacteria in intact cell layer were harvested. Bacteria at 4 h, 24 h and 72 h were plated on 7H10 agar plates in triplicate, plates were incubated for 3 weeks at 37°C and CFU (colony forming unit) were counted [13].…”

“…After neutralization and centrifugation, the suspension of the pellet was inoculated on Lowenstein-Jensen (L-J) medium. The visible growth of colonies on L-J medium was identified using conventional biochemical method [13].…”

The Interplay of Human and Mycobacterium Tuberculosis Genomic Variability

“…High virulence strains also replicated faster in the macrophages and induced lower secretion of tumor necrosis factor α (TNF-α) and IL-6, but higher production of IL-1β. This high virulence bacterial phenotype was strongly associated with lineage 2 strains (Tram et al, 2018). However, this study did not address a possible “fit” between host and Mtb genetic background.…”