Cell-wall deficient L. monocytogenes L-forms feature abrogated pathogenicity

Barbara Schnell, Titu Staubli, Nicola L. Harris, Gerhard Rogler, Manfred Kopf, Martin J. Loessner, Markus Schuppler

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12 Citations (Scopus)


Stable L-forms are cell wall-deficient bacteria which are able to multiply and propagate indefinitely, despite the absence of a rigid peptidoglycan cell wall. We investigated whether L-forms of the intracellular pathogen L. monocytogenes possibly retain pathogenicity, and if they could trigger an innate immune response. While phagocytosis of L. monocytogenes L-forms by non-activated macrophages sometimes resulted in an unexpected persistence of the bacteria in the phagocytes, they were effectively eliminated by IFN-γ preactivated or bone marrow-derived macrophages (BMM). These findings were in line with the observed down-regulation of virulence factors in the cell-wall deficient L. monocytogenes. Absence of Interferon-β (IFN-β) triggering indicated inability of L-forms to escape from the phagosome into the cytosol. Moreover, abrogated cytokine response in MyD88-deficient dendritic cells (DC) challenged with L. monocytogenes L-forms suggested an exclusive TLR-dependent host response. Taken together, our data demonstrate a strong attenuation of Listeria monocytogenes L-form pathogenicity, due to diminished expression of virulence factors and innate immunity recognition, eventually resulting in elimination of L-form bacteria from phagocytes.

Original languageEnglish
Article number60
Number of pages11
JournalFrontiers in Cellular and Infection Microbiology
Issue numberMAY
Publication statusPublished - 1 Jan 2014
Externally publishedYes


  • Innate immunity
  • L-forms
  • L. monocytogenes
  • Pathogenicity
  • Virulence genes

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