Mycobacterium tuberculosis CDC1551 induces a more vigorous host response in vivo and in vitro, but is not more virulent than other clinical isolates

Mycobacterium tuberculosis CDC1551, a clinical isolate reported to be hyper virulent and to grow faster than other isolates, was compared with two othe r clinical isolates (HN60 and HN878) and two laboratory strains (H37Rv and Erdman), The initial (2-14 days) growth of CDC1551; HN60, HN878, and H37Rv was similar in the lungs of aerosol-infected mice, but growth of Erdman was slower, Thereafter, the growth rate of CDC1551 decreased relative to the o ther strains which continued to grow at comparable rates up to day 21, In-t he lungs of CDC1551-infected mice, small well-organized granulomas with hig h levels of TNF-alpha, IL-6, IL-10, IL-12, and IFN-gamma mRNA were apparent sooner than in lungs of mice infected with the other strains. CDC1551-infe cted mice survived significantly longer. These findings were confirmed in v itro. The growth rate of HR37Rv and CDC1551 in human monocytes were the sam e, but higher levels of TNF-alpha IL-10, IL-6, and IL-12 were induced in mo nocytes after infection with CDC1551 or by exposure of monocytes to lipid f ractions from CDC1551, CD14 expression on the surface of the monocytes was up-regulated to a greater extent by exposure to the lipids of CDC1551. Thus , CDC1551 is not more virulent than other M. tuberculosis isolates in terms -of growth in vivo and in vitro, but it induces a more rapid and robust hos t response.