The Entomopathogenic Nematode-Bacterium Complex: Biology, Life Cycle and Vertebrate Safety

Abstract

This paper reports on several aspects of the taxonomy and biology of the symbiotic bacteria, Xenorhabdus spp. and Photorhabdus spp., associated with entomopathogenic nematodes (EPNs), which may be used to define the boundaries with pathogenic bacteria of medical, veterinary or agronomic importance. All the result of tests undertaken to assess the effects of these bacteria on warm-blooded vertebrates were negative, indicating that the bacteri would pose no hazard to vertebrates in practice. Non-symbiotic microorganisms are also associated occasionally with EPNs, and some of them, e.g Providencia rettgeri, belong to taxa which include opportunistic pathogens of man. This review emphasizes that the relationship between these non-symbiotic bacteria and nematodes cannot be considered to be a risk for humans because they do not support the growth of nematodes during long-term mass rearing or they do not persist during storage of nematodes, so their purposeful use is necessarily excluded for industrial production. Good practice by biotechnology laboratories can avoid such contaminants. However, commercial producers should be aware of the possible occurrence of human opportunistic pathogens and prevent such contaminations by establishing monoxenic symbiotic cultures. The pathogenic properties of both partners of the normal bacterium-EPN complex are examined with respect to the risks they pose to human and vertebrate health and to the environment. It is concluded that no risk to warm-blooded animals or plants is related to the use of EPNs in biological control.