Resuscitation of viable but nonculturable Legionella pneumophila philadelphia JR32 by Acanthamoeba castellanii

Michael Steinert, Levente Emödy, Rudolf Amann, Jörg Hacker

Research output: Contribution to journalArticle

284 Citations (Scopus)


Legionella pneumophila is an aquatic bacterium and is responsible for Legionnaires' disease in humans. Free-living amoebae are parasitized by legionellae and provide the intracellular environment required for the replication of this bacterium. In low-nutrient environments, however, L. pneumophila is able to enter a non-replicative viable but nonculturable (VBNC) state. In this study, L. pneumophila Philadelphia I JR 32 was suspended in sterilized tap water at 104 cells/ml. The decreasing number of bacteria was monitored by CFU measurements, acridine orange direct count (AODC), and hybridization with 16S rRNA-targeted oligonucleotide probes. After 125 days of incubation in water, the cells were no longer culturable on routine plating media; however, they were still detectable by AODC and by in situ hybridization. The addition of Acanthamoeba castellanii to the dormant bacteria resulted in the resuscitation of L. pneumophila JR 32 to a culturable state. A comparison of plate-grown legionellae and reactivated cells showed that the capacity for intracellular survival in human monocytes and intraperitoneally infected guinea pigs, which is considered a parameter for virulence, was not reduced in the reactivated cells. However, reactivation of dormant legionellae was not observed in the animal model.

Original languageEnglish
Pages (from-to)2047-2053
Number of pages7
JournalApplied and environmental microbiology
Issue number5
Publication statusPublished - May 1 1997

ASJC Scopus subject areas

  • Biotechnology
  • Food Science
  • Applied Microbiology and Biotechnology
  • Ecology

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