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, CHUV Hospital,
Bugnon 46, 1011 Lausanne, Switzerland.
Abstract
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.
Keywords: Free-living amoebae; amoeba-resisting
bacteria; Hartmannella vermiformis; Legionella
pneumophila; Bradyrhizobium japonicum;Rhodoplanes,
Methylobacterium, Bradyrhizobium, Afipia, and
Bosea;taxonomy.
Corresponding author: Tel.: 41 21 31 44
979. Fax: 41 21 31 44 060
E-mail: Gilbert.Greub@chuv.ch
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