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CHARACTERIZATION OF A PREVIOUSLY UNDESCRIBED LAGENIDIUM PATHOGEN
ASSOCIATED WITH SOFT TISSUE INFECTION: INITIAL DESCRIPTION OF A NEW
HUMAN OOMYCOSIS
Grooters AM1, Proia LA2, Sutton DA3, Hodgin EC1 1Louisiana State University School of Veterinary Medicine, Baton Rouge, USA 2Rush University Medical Center, Chicago, USA 3University of Texas Health Science Center at San Antonio, San Antonio, USA The genus Lagenidium in the class Oomycetes includes more than 50 species, most of which occuras parasites of algae, fungi, nematodes, crustaceans, or insect larvae. It was first recognized as amedically important genus in 1999, when a previously undescribed species of Lagenidium wasidentified as a cause of subcutaneous and systemic disease in dogs. More recently, the authors haveisolated a second pathogenic Lagenidium species from tissues obtained from four dogs and oneperson with chronic subcutaneous infections. The purpose of this report is to characterize this newlyrecognized pathogen, and to describe for the first time the clinicopathologic features associated withLagenidium sp infection in a human patient.
Clinical findings in both the human and canine patients were characterized by progressive deepcellulitis (often with numerous draining tracts) involving one or more extremities. Amputation wascurative in two dogs with lesions limited to a single distal extremity, and repeated aggressive surgicalresection combined with longterm itraconazole and terbinafine administration was curative in a dogwith multiple recurrent cutaneous lesions. In the human patient, chronic cellulitis involving a singledistal lower extremity failed to respond to voriconazole but later showed marked improvement afteradministration of posaconazole. Histologically, lesions were characterized by granulomatousinflammation centered around broad, infrequently septate hyphae; eosinophilic inflammation,necrosis, and suppuration were variably present. Immunoblot analysis of the serologic response ofthree affected dogs to soluble mycelial extracts of L. giganteum and of the previously describedpathogenic Lagenidium species was performed, and indicated that each dog’s serum recognized alarge number of antigens of both Lagenidium species.
Culture of affected canine tissues on peptone-yeast-glucose agar at 30C for 3 days yielded growthof a colorless to white mostly submerged colony. The human isolate produced small, restricted,heaped, white to cream-colored colonies approximately 3 to 5 mm in diameter after 10 days incubationat 25C on potato flakes agar. Short hyphal fragments of varying widths (10 - 30 um) were present;however large, globose to oval-shaped cells ( to 116 um in diameter) were the prominent feature.
Molecular identification of the isolates was performed by amplifying and sequencing the 18s and ITSregions of the ribosomal RNA gene. The 18s region shared 97.3% identity with Lagenidiumgiganteum, 97.3% identity with the previously described pathogenic Lagenidium species, 96.2% withL. myophilum, and 96.1% with L. humanum. In the ITS region, three of the canine isolates wereidentical, with the fourth canine isolate and the human isolate differing from the other three by 2 bpeach. In comparison with other Lagenidium species, the ITS region of the clinical isolates shared65.8% identity with the previously described pathogenic Lagenidium species, 65.7% identity with bothL. giganteum and L. humanum, and 60.3% identity with L. myophilum. Cladistic analysis supportedplacement of the clinical isolates in the Family Pythiales.
The discovery of a second mammalian pathogen in the genus Lagenidium and the identification forthe first time of Lagenidium sp infection in a human patient suggest that the oomycetes represent anemerging and possibly underdiagnosed group of medically important pseudofungi.
Focus on Fungal Infections 14

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