Abstract

The genus Photorhabdus can be split into 3 species based on multi-locus sequence typing. Two of these species are associated with an insect pathogenic nematode worm in a “symbiosis” of pathogens. Nematode-bacterial complexes containing these Photorhabdus strains have been routinely used as crop-protection agents for some time now. The third species, P. asymbiotica, has however only been isolated as the causal agent of clinical infections and may be considered an “emerging” human pathogen. It is suspected that the micro-organisms that cause “emerging diseases” are already present in the environment, often on other animal hosts, which somehow acquire pathogenesis to humans. When we consider the numbers of invertebrate animals in the environment and the frequency and intimacy by which they come into contact with humans, it may be unwise to underestimate their role in the evolution of mammalian disease. The similarities between the “innate” immunity of insects and man mean that it is likely that bacterial pathogens evolved to overcome insect immunity can be pre-adapted for mammalian hosts. I will discuss the molecular adaptations that have allowed an emerging bacterial pathogen, P. asymbiotica, to infect humans, and describe our recent findings from both comparative genomic work and clinical data.