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Applied and Environmental Microbiology, May 2005, p. 2244-2249, Vol. 71, No. 5
0099-2240/05/$08.00+0     doi:10.1128/AEM.71.5.2244-2249.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.

Balamuthia mandrillaris, Free-Living Ameba and Opportunistic Agent of Encephalitis, Is a Potential Host for Legionella pneumophila Bacteria

Winlet Sheba Shadrach,1 Kerstin Rydzewski,1 Ulrike Laube,2 Gudrun Holland,3 Muhsin Özel,3 Albrecht F. Kiderlen,2* and Antje Flieger1

Robert Koch-Institut, Research Group Pathogenesis of Legionella Infections, Nordufer 20, 13353 Berlin, Germany,1 Robert Koch-Institut, Cellular Immunology Unit, Nordufer 20, 13353 Berlin, Germany,2 Robert Koch-Institut, Rapid Diagnostics Unit, Nordufer 20, 13353 Berlin, Germany3

Received 29 March 2004/ Accepted 2 December 2004

Balamuthia mandrillaris is a free-living ameba and an opportunistic agent of granulomatous encephalitis in humans and other mammalian species. Other free-living amebas, such as Acanthamoeba and Hartmannella, can provide a niche for intracellular survival of bacteria, including the causative agent of Legionnaires' disease, Legionella pneumophila. Infection of amebas by L. pneumophila enhances the bacterial infectivity for mammalian cells and lung tissues. Likewise, the pathogenicity of amebas may be enhanced when they host bacteria. So far, the colonization of B. mandrillaris by bacteria has not been convincingly shown. In this study, we investigated whether this ameba could host L. pneumophila bacteria. Our experiments showed that L. pneumophila could initiate uptake by B. mandrillaris and could replicate within the ameba about 4 to 5 log cycles from 24 to 72 h after infection. On the other hand, a dotA mutant, known to be unable to propagate in Acanthamoeba castellanii, also did not replicate within B. mandrillaris. Approaching completion of the intracellular cycle, L. pneumophila wild-type bacteria were able to destroy their ameboid hosts. Observations by light microscopy paralleled our quantitative data and revealed the rounding, collapse, clumping, and complete destruction of the infected amebas. Electron microscopic studies unveiled the replication of the bacteria in a compartment surrounded by a structure resembling rough endoplasmic reticulum. The course of intracellular infection, the degree of bacterial multiplication, and the ultrastructural features of a L. pneumophila-infected B. mandrillaris ameba resembled those described for other amebas hosting Legionella bacteria. We hence speculate that B. mandrillaris might serve as a host for bacteria in its natural environment.

* Corresponding author. Mailing address: Robert Koch-Institut, Cellular Immunology Unit, Nordufer 20, D-13353 Berlin, Germany. Phone: 49 30 4547-2298. Fax: 49 30 4547-2694. E-mail: a.kiderlen{at}rki.de.

Applied and Environmental Microbiology, May 2005, p. 2244-2249, Vol. 71, No. 5
0099-2240/05/$08.00+0     doi:10.1128/AEM.71.5.2244-2249.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.



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