Effect of the deletion of lprG and p55 genes in the K10 strain of Mycobacterium avium subspecies paratuberculosis

Evaluation of the cytotoxicity and antibacterial activity of a synthetic tunicamycin derivative against Mycobacterium avium complex

Two synthetic derivatives of the tunicamycin antibiotic, TunR1 and TunR2, were previously developed that significantly reduced toxicity in eukaryotes but remained potent against Gram positive prokaryotes. TunR2 has been demonstrated to be non-toxic and effective in a zebrafish model of mycobacterial infection. In this study, we evaluated the cytotoxicity in bovine cells and the antibacterial effect of natural Tun as well as two synthetic derivatives of Tun, designated TunR1 and TunR2, on Mycobacterium avium complex. The average minimal inhibitory concentration (MIC) and minimal bactericidal concentration (MBC) for TunR2 ranged from 16 to 32 μg/mL when tested on seven Mycobacterium avium subspecies paratuberculosis (Map) strains. MICs were higher for the closely related Mycobacterium avium subspecies hominissuis (>32 μg/mL), and lower for Mycobacterium marinum (0.025 μg/mL) and Mycobacterium smegmatis (3.2 μg/mL). Effects on the Map cell wall could be detected by electron microscopy at TunR2 concentrations above 128 μg/mL. The toxicity of TunR2 in eukaryotes was evaluated in vitro by hemolysis of bovine red blood cells (RBCs) and by MTT viability assay on a bovine epithelial cell line, cultured bovine peripheral blood mononuclear cells (PBMCs), and bovine monocyte-derived macrophages (bMDMs). The concentrations of the drug that produce 50% of inhibition (IC50) in each of these three cell types was lower than the MIC for Map. Hemolytic activity was demonstrated in 91% of RBCs when exposed to 31 μg/mL of TunR2. Also, low-dose TunR2 treatment of infected macrophages did not significantly decrease Map survival after 48 h of infection. These results suggest that TunR2 is not a good candidate to treat Map infections.

Genomic comparison of two strains of Mycobacterium avium subsp. paratuberculosis with contrasting pathogenic phenotype

In a previous study, we evaluated the degree of virulence of Mycobacterium avium subsp. paratuberculosis (Map) strains isolated from cattle in Argentina in a murine model. This assay allowed us to differentiate between high-virulent MapARG1347 and low-virulent MapARG1543 strains. To corroborate whether the differences in virulence could be attributed to genetic differences between the strains, we performed Whole Genome Sequencing and compared the genomes and gene content between them and determined the differences related to the reference strain MapK10. We found 233 SNPs/INDELS in one or both strains relative to Map K10. The two strains share most of the variations, but we found 15 mutations present in only one of the strains. Considering NS-SNP/INDELS that produced a severe effect in the coding sequence, we focus the analysis on four predicted proteins, putatively related to virulence. Survival of MapARG1347 strain in bMDM was higher than MapARG1543 and was more resistant to acidic pH and H₂O₂ stresses than MapK10. The genomic differences between the two strains found in genes MAP1203 (a putative peptidoglycan hydrolase), MAP0403 (a putative serine protease) MAP1003c (a member of the PE-PPE family) and MAP4152 (a putative mycofactocin binding protein) could contribute to explain the contrasting phenotype previously observed in mice models.

Comparative Analysis on Proteomics Profiles of Intracellular and Extracellular M.tb and BCG From Infected Human Macrophages

Tuberculosis is the second cause in infectious diseases leading to human death. Understanding the virulence mechanism is inevitable if the disease needs to be fully cured. Therefore, this study aimed to reveal this mechanism by comparing proteomic profiles of intracellular and extracellular virulent strain M.tb and bacille Calmette–Guérin (BCG) from infected THP-1cells. First, M.tb and BCG infected THP-1 at MOI 10:1. Twelve hours postinfection, intracellular bacteria of M.tb and BCG were collected, whereas the two bacilli cultured in 7H9 broth media were used as the control. Then four groups of bacilli were subjected to proteomic analysis, and differential proteomic profiles between M.tb and BCG were comparatively analyzed with bioinformatics tools. As a result, we identified a total of 1,557 proteins. Further, they were divided into four groups for comparison of M.tb versus BCG under 7H9 culture (shorten as out), M.tb in (intracellular) versus M.tb out, BCG in versus BCG out and M.tb in versus BCG in. Between M.tb in versus BCG in, a total of 211 differentially expressed proteins were found. Eight proteins like ESAT-6 distributed in six RDs and some known proteins related to virulence. Besides, five uncharacterized proteins were differentially expressed. Further analysis revealed enriched pathways were associated with glyoxylate and dicarboxylate metabolism pathways. In M.tb out versus BCG out, a total of 144 differential proteins were identified and mainly involved in metabolism pathways. Then, 121 differential proteins in the group of M.tb in versus M.tb out were enriched in ribosome and oxidative phosphorylation related to adaptation to the host environment. The group of BCG in versus BCG out shared the same trend of different pathways to the M.tb in versus M.tb out. Finally, 42 proteins were identified to be up-regulated only in intracellular M.tb including eight RD proteins, whereas 22 up-regulated uniquely in intracellular BCG. Besides, only two proteins (Pks13 and Rv1405c) were commonly up-regulated in intracellular M.tb and BCG. Further, some unknown proteins were uniquely up-regulated in the intracellular M.tb and BCG. These findings provide valuable data for further exploration of molecular mechanism for M.tb virulence and BCG immune response.