Isolation, identification, and molecular characterization of strains of Photorhabdus luminescens from infected humans in Australia

We describe the isolation of Photorhabdus (Xenorhabdus) luminescens from fo ur Australian patients: two with multiple skin lesions, one with bacteremia only, sind one with disseminated infection. One of the patients had multip le skin lesions following the bite of a spider, while the lesions in the ot her patient were possibly associated with a spider bite. The source of infe ction for the remaining two patients is unknown. As a member of the family Enterobacteriaceae, P. luminescens is unusual in that it fails to reduce ni trate and ferments only glucose and mannose. It gives negative reactions fo r lysine decarboxylase, arginine dihydrolase, and ornithine decarboxylase ( Moeller). The species is motile, utilizes citrate, hydrolyzes urea, and usu ally produces a unique type of annular hemolysis on sheep blood agar plates incubated at 25 degrees C. A weak bioluminescence is the defining characte ristic. P. luminescens is an insect pathogen and is symbiotically associate d with entomopathogenic nematodes. Its isolation from human clinical specim ens has been reported previously from the United States. Restriction fragme nt length polymorphism-PCR analysis of the 16S rRNA gene demonstrated a hig h level of similarity among the Australian clinical strains and significant differences between the Australian clinical strains and the U.S. clinical strains. However, numerical analyses of the data suggest that the two group s of clinical strains are more similar to each other than they are to the s ymbiotic strains found in nematodes. This is the first report of the isolat ion of P. luminescens from infected humans in Australia and the second repo rt of the isolation of this species from infected humans worldwide.