1887

Abstract

, a Gram-negative anaerobe, causes a variety of necrotic infections in humans and animals. There are two subspecies: subsp. and subsp. . In cattle, subsp. is more prevalent and production of leukotoxin is a major virulence factor. The leukotoxin operon () consists of three genes, , and , of which is the structural toxin gene. The subspecies identity of human is less certain and it is not known whether human strains possess the leukotoxin gene or leukotoxin activity. Therefore, the objective of this study was to identify the subspecies status of four human clinical strains of and determine whether they have the leukotoxin gene or leukotoxin activity. Phenotypic and genotypic characteristics suggested that the four strains belonged to subsp. , which was confirmed by sequencing the 16S rRNA gene. Analysis of the four strains by PCR revealed the presence of the leukotoxin operon. Partial DNA sequencing identified one human strain with full-length , whereas the others exhibited considerable heterogeneity in size. All strains had a leukotoxin operon promoter-containing intergenic region similar to that of bovine subsp. strains, which was confirmed by DNA sequencing and Southern blotting. Despite variations in the gene, all strains secreted leukotoxin as demonstrated by Western blotting. Flow cytometry assays revealed that the leukotoxin was toxic to human white blood cells. In conclusion, the human strains examined contained a leukotoxin gene whose gene product was biologically active. The importance of leukotoxin as a virulence factor in human fusobacterial infections needs further evaluation.

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2008-02-01
2024-03-28
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