Search

Fusarium oxysporum is a phylogenetically diverse monophyletic complex of filamentous ascomycetous fungi that are responsible for localized and disseminated life-threatening opportunistic infections in immunocompetent and severely neutropenic patients, respectively. Although members of this complex were isolated from patients during a pseudoepidemic in San Antonio, Tex., and from patients and the water system in a Houston, Tex., hospital during the 1990s, little is known about their genetic relatedness and population structure. This study was conducted to investigate the global genetic diversity and population biology of a comprehensive set of clinically important members of the F. oxysporum complex, focusing on the 33 isolates from patients at the San Antonio hospital and on strains isolated in the United States from the water systems of geographically distant hospitals in Texas, Maryland, and Washington, which were suspected as reservoirs of nosocomial fusariosis. In all, 18 environmental isolates and 88 isolates from patients spanning four continents were genotyped. The major finding of this study, based on concordant results from phylogenetic analyses of multilocus DNA sequence data and amplified fragment length polymorphisms, is that a recently dispersed, geographically widespread clonal lineage is responsible for over 70% of all clinical isolates investigated, including all of those associated with the pseudoepidemic in San Antonio. Moreover, strains of the clonal lineage recovered from patients were conclusively shown to genetically match those isolated from the hospital water systems of three U.S. hospitals, providing support for the hypothesis that hospitals may serve as a reservoir for nosocomial fusarial infections.

Phialemonium obovatum was found to be the cause of nosocomial osteomyelitis in a 41-year-old man after sustaining a nonpenetrating injury to his lumbar and cervical region. Histologic examination of fragments of disk and bone from L3-4 hemilaminectomy showed multiple fragments of fibrocartilage with focal necrosis, chronic inflammation, and granulation tissue formation. Sections stained with Gomori's methenamine silver procedure showed multiple fungal elements in necrotic areas consisting of irregularly branched, hyaline septate hyphae having swollen cells, and occasional yeastlike cells. The use of Fontana-Masson silver stain showed the presence of melanin in cells walls and septa of the hyphae. Phialemonium obovatum was isolated when the ground tissue from disk and bone from L3-4 was cultured on biphasic brain-heart infusion medium. Colonies were moist, off-white to ochraceous with a characteristic green, diffusible pigment on the reverse side. The isolate grew well up to 40 degrees C. It formed characteristic adelophialides without conspicuous collarettes and basal septa and produced smooth, one-celled, hyaline, and obovate conidia.