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Low-level iron-dependent mutants of Listeria monocytogenes and their virulence in macrophages

Canadian Journal of Microbiology, ISSN: 0008-4166, Vol: 49, Issue: 2, Page: 78-84
2003
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Article Description

Listeria monocytogenes is an opportunistic intracellular pathogen capable of growth within phagocytic cells that requires iron for growth and virulence expression. In the presence of an appropriate concentration of tropolone, an iron-chelating agent, growth of L. monocytogenes is completely inhibited. However, this inhibition can be relieved by addition of dopamine, norepinephrine, or ferric citrate. By selection on streptonigrin medium supplemented with tropolone and norepinephrine, we have obtained two spontaneous mutants, Lm-8 and Lm-15, with the same iron dependence but lower iron dependence than the wild-type Lm-B38. The association between iron requirement and virulence of the two mutants and the wild type was studied in the J774 macrophage cell line. One hour after phagocytosis by the J774 macrophage cell line, the two mutants and the parental strain displayed no difference in the number of phagocytosed bacteria. Twenty-four hours after phagocytosis, the number of bacteria within the surviving macrophages was identical for the wild strain and the two clones. However, only 40% of macrophage cells infected with Lm-8 and 90% of those infected with Lm-15 were alive after 24 h in comparison with macrophage cells infected with the parental strain Lm-B38. These data demonstrate that there is no direct correlation between iron requirement and virulence of L. monocytogenes in the J774 macrophage cell line.

Bibliographic Details

Andre, Philippe; Oberle, Stéphanie; Specklin, Véronique; Lombard, Yves; Vidon, Dominique Jean-Marie

Canadian Science Publishing

Immunology and Microbiology; Biochemistry, Genetics and Molecular Biology

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