Mycobacterium tuberculosis (MTB) infection has become a growing health risk as multi-drug resistant strain (MDR-MTB) has emerged worldwide. The development of isoniazid (INH)-resistant M. tuberculosis strains dictate the need to re-design this old drug to create effective analogs against the resistant INH strains. Synthesis and the biological activity of isoniazid and pyridine derivatives were successfully carried out with elaborated characterization by spectral data. Amongst the synthesized compounds; 1 and 2 displayed encouraging antimycobacterial activity with IC50 of 3.2 mu M and 1.5 mu M against the H37Rv strain. The MIC of test compounds 1 and 2 were also assessed against the 5 drug resistant isolates (FQ-R1, INH-R1, INH-R2, RIF-R1 and RIF-R2) of MTB strains under aerobic conditions and compound 1 [MIC = 3.2 mu M for FQ-R1; MIC = 140 mu M for INH-R1; MIC = 160 mu M for INH-R2; MIC = 2.4 mu M towards RIF-R1; MIC = 4.2 mu M for RIF-R2] and 2 [MIC = 3.3 mu M for FQ-R1; MIC = 170 mu M for INH-R1; MIC= 190 mu M for INH-R2; MIC= 1.8 mu M for RIF-R1; MIC= 8.4 mu M for RIF-R2] have shown significant activity at non-cytotoxic concentration in comparison to the standard drug.

Objectives: Recurrent tuberculosis (TB) is defined by more than one TB episode per patient and is caused by reinfection with a new M. tuberculosis (Mtb) strain or relapse with the previous strain. In Denmark, a major TB outbreak caused by one specific Mtb genotype "DKC2" is ongoing. Of the 892 patients infected with DKC2 between 1992 and 2014, 32 had recurrent TB with 67 TB episodes in total. Methods: The 32 cases were evaluated in terms of number of single-nucleotide polymorphism (SNP) differences and time between episodes derived from whole-genome sequencing data. Results: For four TB cases, the subsequent episodes could be confirmed as relapse and for one case as reinfection. Eight cases with SNP differences < 6, theoretically indicating relapse, could be classified as likely reinfections based on phylogenetic analysis in combination with geographical data. Subsequent TB episodes for the remaining 19 cases could not be classified as relapse or reinfection even though they all had a SNP difference of < 6 SNPs. Conclusions: In newer studies, investigating recurrent TB with the use of WGS, the number of SNPs has been used to distinguish between relapse and reinfection. The algorithm proposed for this is not valid in the Danish TB outbreak setting as our findings challenge the interpretation of few SNP differences as representing relapse. However, when including phylogenetic analysis and geographical data in the analysis, classification of 13 of the 32 cases were possible.