The rhizosphere as a reservoir for opportunistic human pathogenic bacteria


  • Gabriele Berg,

    Corresponding author
    1. University of Rostock, Department of Life Sciences, Institute of Microbiology, Albert-Einstein-Straße 3, D-18051 Rostock, Germany.
      *E-mail; Tel. (+49) 381 4986154; Fax (+49) 381 4986152.
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  • Leo Eberl,

    1. University of Zürich, Institute of Plant Biology, Department of Microbiology, Zollikerstraße 107, CH-8008 Zürich, Switzerland.
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  • Anton Hartmann

    1. GSF – National Research Center for Environment and Health, Institute of Soil Ecology, Department of Rhizosphere Biology, Ingolstaedter Landstraße 1, D-85764 Neuherberg/Munich, Germany.
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*E-mail; Tel. (+49) 381 4986154; Fax (+49) 381 4986152.


During the last years, the number of human infections caused by opportunistic pathogens has increased dramatically. One natural reservoir of opportunistic pathogens is the rhizosphere, the zone around roots that is influenced by the plant. Due to a high content of nutrients, this habitat is a ‘microbial hot-spot’, where bacterial abundances including those with strong antagonistic traits are enhanced. Various bacterial genera, including Burkholderia, Enterobacter, Herbaspirillum, Ochrobactrum, Pseudomonas, Ralstonia, Staphylococcus and Stenotrophomonas, contain root-associated strains that can encounter bivalent interactions with both plant and human hosts. Mechanisms responsible for colonization of the rhizosphere and antagonistic activity against plant pathogens are similar to those responsible for colonization of human organs and tissues, and pathogenicity. Multiple resistances against antibiotics are not only found with clinical strains but also with strains isolated from the rhizosphere. High competition, the occurrence of diverse antibiotics in the rhizosphere, and enhanced horizontal gene transfer rates in this microenvironment appear to contribute to the high levels of natural resistances. While opportunistic bacteria from the rhizosphere have some properties in common, each of these emerging pathogens has its own features, which are discussed in detail for Burkholderia, Ochrobactrum and Stenotrophomonas.