Intracellular growth of two multidrug-resistant Mycobacterium tuberculosis strains with different transmission dynamics

NOEMI YOKOBORI; BEATRIZ LOPEZ; CARMEN SABIO Y GARCIA; PABLO SCHIERLOH; VIVIANA RITACCO; LUCIA BARRERA; MARIA DEL CARMEN SASIAIN

Simposio; IV Reunion de la Sociedad Latinoamerica de tuberculosis y otras micobacteriosis (SLAMTB); 2009

Introduction: Multidrug-resistant tuberculosis (MDR-TB) is a mayor treat to public health. Argentina was declared as a “hot spot” for MDR-TB due to extensive outbreaks that emerged in the early 90’s, mainly due to the aggressive spread of strain M, a highly successful genotype that persists even in our days. Aim: to assess the intracellular growth of strain M compared to that of strain 410, closely related to the prosperous genotype according to the RFLP pattern, but responsible for a single case. Both isolates belong to the Haarlem lineage. Methods: Human monocyte derived macrophages (MÖ) were infected with strain M, 410 and H37Rv for two hours at a multiplicity of infection (MOI) of 10. Cells were washed to remove extracellular bacteria and cell-associated colony forming units (CFU) were assessed at 0, 2 and 5 days of infection in solid medium (7H9/OADC). To assess intracellular bacilli, infected MÖ were Ziehl-Neelsen stained at the same time points. Results: Although the percentage of infected cells was similar in both MDR strains (M: 58±5%; 410: 54±3) our results show that strain 410 grew faster than M (On day 5, M: 1387±200 CFU/ml; 410: 2507±269; H37Rv: 1770±425, Mean±SEM. M vs. 410: p<0.05) probably due to a shorter lag phase. Conclusion: The ability of replicating within the MÖ has been proposed as a measure of virulence for clinical isolates, but in our hands this single parameter does not explain by itself the epidemiological success of strain M.