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Applied and Environmental Microbiology, April 2006, p. 2428-2438, Vol. 72, No. 4
0099-2240/06/$08.00+0     doi:10.1128/AEM.72.4.2428-2438.2006
Copyright © 2006, American Society for Microbiology. All Rights Reserved.

Biodiversity of Amoebae and Amoeba-Resisting Bacteria in a Hospital Water Network

Vincent Thomas,1 Katia Herrera-Rimann,1 Dominique S. Blanc,2 and Gilbert Greub1*

Center for Research on Intracellular Bacteria, Institute of Microbiology, Faculty of Biology and Medicine, University of Lausanne, Lausanne, Switzerland,1 Hospital of Preventive Medicine, University Hospital of Lausanne, Lausanne, Switzerland2

Received 28 July 2005/ Accepted 20 January 2006

Free-living amoebae (FLA) are ubiquitous organisms that have been isolated from various domestic water systems, such as cooling towers and hospital water networks. In addition to their own pathogenicity, FLA can also act as Trojan horses and be naturally infected with amoeba-resisting bacteria (ARB) that may be involved in human infections, such as pneumonia. We investigated the biodiversity of bacteria and their amoebal hosts in a hospital water network. Using amoebal enrichment on nonnutrient agar, we isolated 15 protist strains from 200 (7.5%) samples. One thermotolerant Hartmannella vermiformis isolate harbored both Legionella pneumophila and Bradyrhizobium japonicum. By using amoebal coculture with axenic Acanthamoeba castellanii as the cellular background, we recovered at least one ARB from 45.5% of the samples. Four new ARB isolates were recovered by culture, and one of these isolates was widely present in the water network. Alphaproteobacteria (such as Rhodoplanes, Methylobacterium, Bradyrhizobium, Afipia, and Bosea) were recovered from 30.5% of the samples, mycobacteria (Mycobacterium gordonae, Mycobacterium kansasii, and Mycobacterium xenopi) were recovered from 20.5% of the samples, and Gammaproteobacteria (Legionella) were recovered from 5.5% of the samples. No Chlamydia or Chlamydia-like organisms were recovered by amoebal coculture or detected by PCR. The observed strong association between the presence of amoebae and the presence of Legionella (P < 0.001) and mycobacteria (P = 0.009) further suggests that FLA are a reservoir for these ARB and underlines the importance of considering amoebae when water control measures are designed.

* Corresponding author. Mailing address: Center for Research on Intracellular Bacteria, Institute of Microbiology, CHUV Hospital, Bugnon 46, 1011 Lausanne, Switzerland. Phone: 41 21 31 44 979. Fax: 41 21 31 44 060. E-mail: Gilbert.Greub{at}chuv.ch.

Applied and Environmental Microbiology, April 2006, p. 2428-2438, Vol. 72, No. 4
0099-2240/06/$08.00+0     doi:10.1128/AEM.72.4.2428-2438.2006
Copyright © 2006, American Society for Microbiology. All Rights Reserved.



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