A Review of Clinical Cases of Infection with Photorhabdus Asymbiotica.

The three recognised Photorhabdus species are bioluminescent Gram-negative bacilli of the family Enterobacteriaceae. They are all pathogenic to insects and form a symbiotic relationship with nematodes of the genus Heterorhabditis. P. luminescens and P. temperata are both harmless to humans whilst P. asymbiotica, on the other hand, is a human pathogen that is a symbiont of the newly described nematode vector, Heterorhabditis gerrardi. In this chapter, we review the epidemiological and clinical features of eighteen human cases of P. asymbiotica infection including fifteen from the published literature and three previously unreported cases. Human infection has been reported in the USA and Australia and probably occurs in other parts of Asia where it remains undocumented. Infection occurs most commonly in warmer months particularly after rainfall. Patients may have a history of recent exposure to sand or sandy soil. P. asymbiotica causes both locally invasive soft tissue infection and disseminated disease with bacteraemia. Soft tissue infection may be multifocal with involvement of more than one limb and the trunk. The organism is sensitive to a number of antibiotics in vitro, but treatment failures have been associated with the use of beta-lactams and aminoglycosides. We suggest treatment with a four-week course of an oral fluoroquinolone such as ciprofloxacin. The organism grows readily on standard media from specimens such as wound swabs, pus, blood and even sputum and can be identified in a clinical microbiology laboratory but the diagnosis needs to be considered. The correct diagnosis is most likely to be made where there is close cooperation between clinician and microbiologist.

Actinotignum (formerly Actinobaculum) schaalii: a review of MALDI-TOF for identification of clinical isolates, and a proposed method for presumptive phenotypic identification.

Actinotignum schaalii is a recognised cause of urinary tract infection. Following a case of urosepsis, 20 isolates of A. schaalii were collected over an initial 18 month period from urine and blood culture. An additional 25 isolates were collected over the following 13 months. Actinotignum schaalii had likely been overlooked or dismissed as a contaminant in our laboratory prior to this study period. It grows slowly on blood agar with supplemental CO2 or anaerobically. It may not grow on MacConkey agar or chromogenic agars used for routine urine culture. Repeated attempts at identification by matrix-assisted laser desorption/ionisation time-of-flight mass spectrometry (MALDI-TOF MS) may be required as the optimal age of cultures for testing is unclear. Utilising its characteristic antibiogram may assist phenotypic identification of this organism which is otherwise difficult to distinguish from other actinomycetes.