The three currently recognised Photorhabdus species are bioluminescent bacteria that are pathogenic to insects. P luminescens and R temperata form a symbiotic relationship with nematodes that infect insects. P asymbiotica, on the other hand, has only been isolated from human clinical specimens from the USA and Australia. The bacterium has been associated with locally invasive soft tissue and disseminated bacteraemic infections. An invertebrate vector for P. asymbiotica has not yet been identified.