Photorhabdus asymbiotica in cases of human infection

Photorhabdus asymbiotica is a potential cause of severe soft tissue and systemic infection in Australia. The clinical and laboratory features have been described in a recent publication.¹ Recognition of this unusual pathogen presents a challenge for clinical microbiology laboratories. It is a bioluminescent gram-negative bacillus and is a member of the Enterobacteriaceae. It produces a thin zone of annular haemolysis on trypt   ic soy agar containing either 5 per cent sheep or horse blood and tends to swarm.

Some isolates produce a yellow pigment and all are faintly luminescent in total darkness. This species is not yet included in the databases of commercial bacterial identification systems. Use of the MicroScan Walkaway (Dade Behring Inc., Sacramento, CA), Vitek (bioMérieux, Hazlewood, MO) or API 20E (bioMérieux, Marcy l'Etoile, France) will result in incorrect identification. The results obtained with these three systems for six Australian isolates of P. asymbiotica are shown in the Table.

Table. Misidentification of Australian isolates of P. asymbiotica by commercial Vitek GNI, Microscan Walkaway Neg BP combo 11, Microscan Walkaway Rap Neg BP 5A and API 20E panels

It is possible that infection due to this species is under-reported due to incorrect laboratory identification. Knowledge of the epidemiology of infection due to P. asymbiotica is incomplete. For example, it has only ever been isolated from clinical specimens and no reservoir or source has been identified. We wish to raise awareness of this infection among clinicians and laboratory workers in the hope of improving case identification. We would be grateful to receive information and isolates from other cases of this condition.

Reference

1. Gerrard JG, McNevin S, Alfredson D, Forgan-Smith R, Fraser N. Photorhabdus species: bioluminescent bacteria as emerging human pathogens? Emerg Infect Dis 2003;9:251-254.

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Author affiliations

1. Director of Medicine, Department of Medicine, Gold Coast Hospital, Southport, Queensland

2. Consultant Microbiologist, Queensland Health Pathology Service, Gold Coast Hospital and Princess Alexandra Hospital, Queensland

3. Director of Microbiology, Queensland Health Pathology Service, Princess Alexandra Hospital, Woolloongabba, Queensland

Corresponding author: Dr John G. Gerrard, Director of Medicine, Department of Medicine, Gold Coast Hospital, Southport, QLD 4215. Telephone: +61 7 5571 8211. Facsimile:+61 7 5571 8996. Email: John_Gerrard@health.qld.gov.au

This article was published in Communicable Diseases Intelligence Volume 27 No 4, December 2003.