Characterization of a Legionella micdadei mip mutant

W. A. O'Connell, J. M. Bangsborg, N. P. Cianciotto*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

37 Scopus citations


The pathogenesis of Legionella micdadei is dependent upon its ability to infect alveolar phagocytes. To better understand the basis of intracellular infection by this organism, we examined the importance of its Mip surface protein. In Legionella pneumophila, Mip promotes infection of both human macrophages and freshwater protozoa. Southern hybridization and immunoblot analyses demonstrated that mip sequences were present and expressed within a panel of virulent L. micdadei strains. Using allelic exchange mutagenesis, we then constructed an L. micdadei strain that completely and specifically lacked Mip. Although unimpaired in its ability to grow in bacteriologic media, this Mip mutant was defective in its capacity to infect U937 cells, a human macrophage-like cell line. Most significantly, the Mip- organism displayed a 24-fold reduction in survivability immediately after its entry into the phagocyte. Similarly, the mutant was less able to parasitize Hartmannella amoebae. Taken together, these data argue that Mip specifically potentiates intracellular growth by L. micdadei.

Original languageEnglish (US)
Pages (from-to)2840-2845
Number of pages6
JournalInfection and immunity
Issue number8
StatePublished - 1995

ASJC Scopus subject areas

  • Infectious Diseases
  • Parasitology
  • Microbiology
  • Immunology


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