The Journal of Experimental Medicine
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© The Rockefeller University Press, 0022-1007/1998/7/49/ $5.00
The Journal of Experimental Medicine, Volume 188, Number 1, July 1, 1998 49-60

Articles

Phase-variable Expression of Lipopolysaccharide Contributes to the Virulence of Legionella pneumophila

Edeltraud Lüneberg*, Ulrich Zähringer{ddagger}, Yuriy A. Knirel{ddagger}, Dorothee Steinmann{ddagger}, Maike Hartmann*, Ivo Steinmetz§, Manfred Rohde||, Jörg Köhl§, and Matthias Frosch*

From the * Institut für Hygiene und Mikrobiologie, Universität Würzburg, 97080 Würzburg, Germany; {ddagger} Forschungszentrum Borstel, 23845 Borstel, Germany; § Institut für Medizinische Mikrobiologie, Medizinische Hochschule, 30625 Hannover, Germany; and || Gesellschaft für Biotechnologische Forschung, 38124 Braunschweig, Germany

With the aid of monoclonal antibody (mAb) 2625, raised against the lipopolysaccharide (LPS) of Legionella pneumophila serogroup 1, subgroup OLDA, we isolated mutant 811 from the virulent wild-type strain RC1. This mutant was not reactive with mAb 2625 and exhibited an unstable phenotype, since we observed an in vitro and in vivo switch of mutant 811 to the mAb 2625–positive phenotype, thus restoring the wild-type LPS. Bactericidal assays revealed that mutant 811 was lysed by serum complement components, whereas the parental strain RC1 was almost serum resistant. Moreover, mutant 811 was not able to replicate intracellularly in macrophage-like cell line HL-60. In the guinea pig animal model, mutant 811 exhibited significantly reduced ability to replicate. Among recovered bacteria, mAb 2625–positive revertants were increased by fourfold. The relevance of LPS phase switch for pathogenesis of Legionella infection was further corroborated by the observation that 5% of the bacteria recovered from the lungs of guinea pigs infected with the wild-type strain RC1 were negative for mAb 2625 binding. These findings strongly indicate that under in vivo conditions switching between two LPS phenotypes occurs and may promote adaptation and replication of L. pneumophila. This is the first description of phase-variable expression of Legionella LPS.

Key Words: Legionella pneumophila • LPS • phase-variation • serum resistance • virulence

Address correspondence to Edeltraud Lüneberg, Institut für Hygiene und Mikrobiologie, Universität Würzburg, Josef-Schneider-Str. 2, 97080 Würzburg, Germany. Phone: 49-931-201-3936; Fax: 49-931-201-3445; E-mail: elueneberg{at}hygiene.uni-wuerzburg.de

This work is dedicated to Dieter Bitter-Suermann on the occasion of his 60th birthday.

Abbreviations used: BYCE, buffered CYE; CI, chemical ionization; CYE, charcoal yeast extract; EI, electron impact; GLC, gas–liquid chromatography; MAC, membrane attack complex; MOMP, major outer membrane protein; NHS, normal human serum; NMR, nuclear magnetic resonance; SG, serogroup.


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