Characterization of the 16S-23S rRNA intergenic spacer regions among strains of the Fusobacterium necrophorum cluster

Detection of Fusobacterium necrophorum subsp. funduliforme in tonsillitis in young adults by real-time PCR

Throat swabs from 61 patients, aged 18-32 years, with non-streptococcal tonsillitis (NST) and 92 healthy controls were examined for the presence of Fusobacterium necrophorum DNA using a novel TaqMan-based real-time quantitative PCR assay for F. necrophorum subspecies. The assay was based on the gyrB subunit gene, and detected F. necrophorum DNA in 48% of patients with NST and in 21% of controls (p <0.001). F. necrophorum subsp. funduliforme was the only subspecies found in both patients and controls. The load of F. necrophorum DNA on swabs from patients with NST was significantly higher than that on swabs from controls (p <0.001). Furthermore, patients with recurrent NST had a significantly higher load of F. necrophorum DNA compared to patients with acute NST (p 0.04). In addition, 26 patients with tonsillitis and group C streptococci (GCS) had a significantly higher load of F. necrophorum DNA compared to the NST group (p <0.001). It was concluded that F. necrophorum subsp. funduliforme is present in small numbers as part of the normal human throat flora, and that F. necrophorum in large quantities may cause tonsillitis, especially recurrent tonsillitis. In addition, the study suggests that the concomitant presence of GCS may aggravate F. necrophorum tonsillitis.

Fusobacterium necrophorum infections in animals: Pathogenesis and pathogenic mechanisms

Fusobacterium necrophorum, a Gram-negative, non-spore-forming anaerobe, is a normal inhabitant of the alimentary tract of animals and humans. Two subspecies of F. necrophorum, subsp. necrophorum (biotype A) and subsp. funduliforme (biotype B), have been recognized, that differ morphologically, biochemically, and biologically. The subsp. necrophorum is more virulent and is isolated more frequently from infections than the subsp. funduliforme. The organism is an opportunistic pathogen that causes numerous necrotic conditions (necrobacillosis), either specific or non-specific infections, in a variety of animals. Of these, bovine liver abscesses and foot rot are of significant concern to the cattle industry. Liver abscesses arise with the organisms that inhabit the rumen gaining entry into the portal circulation, and are often secondary to ruminal acidosis and rumenitis complex in grain-fed cattle. Foot rot is the major cause of lameness in dairy and beef cattle. The pathogenic mechanism of F. necrophorum is complex and not well defined. Several toxins or secreted products, such as leukotoxin, endotoxin, hemolysin, hemagglutinin, proteases, and adhesin, etc., have been implicated as virulence factors. The major virulence factor appears to be leukotoxin, a secreted protein of high molecular weight, active specifically against leukocytes from ruminants. The complete nucleotide sequence of the leukotoxin operon of F. necrophorum has been determined. The operon consists of three genes (lktBAC) of which the second gene (lktA) is the leukotoxin structural gene. The leukotoxin appears to be a novel protein and does not share sequence similarity with any other leukotoxin. F. necrophorum is also a human pathogen and the human strains appear to be different from the strains involved in animal infections.

Phylogenetic analysis of Fusobacterium necrophorum, Fusobacterium varium and Fusobacterium nucleatum based on gyrB gene sequences

The nucleotide sequences of the DNA gyrase B subunit gene (gyrB) of Fusobacterium necrophorum subsp. necrophorum, F. necrophorum subsp. funduliforme and F. varium were determined and analyzed together with those of F. nucleatum subsp. nucleatum and F. nucleatum subsp. vincentii. On the phylogenetic tree constructed, the strains of each fusobacterial species formed distinct clusters with deep sublines. The degree of sequence similarity within each cluster was 93.2% or more, whereas similarities between clusters ranged from 70.1 to 72.7%. These clusters were recovered with 100% bootstrap probabilities and are in very good agreement with the species of Fusobacterium. These data suggest that gyrB is an accurate genealogical marker for the classification of the fusobacterial taxa considered in this study.