Comparative evaluation of selective culture and PCR for detection of Fusobacterium necrophorum and Fusobacterium nucleatum in throat specimens
Tsakris, Athanassios G.
Petrikkos, Georgios L.
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Culture on selective media (Fusobacteriumselective agar supplemented with 4 mg/L vancomycin and 8 mg/L neomycin) was compared to PCR (rpoB and haem genes for Fusobacterium necrophorum, 16S rDNA fragment specific for Fusobacterium nucleatum) for direct detection of the species in throat specimens of 88 patients with sore throat and pharyngotonsilits. Among the 49 culture-positive specimens, culture and PCR revealed identical positive results in 38 (43.1%) and eight (9.1%) patients for F. nucleatum and F. necrophorum, respectively, whilst in two more patients (2.3%), both pathogens were detected by both methods. Only a single F. nucleatum culture-positive specimen was PCR-negative. In contrast, among the remaining 39 culture- negative specimens, five (5.7%) and two (2.3%) were positive by PCR for F. nucleatum and F. necrophorum, respectively. Sub-species identification revealed that all F. necrophorum isolates were identified as F. necrophorumssp. funduliforme. Sensitivity, specificity, PPV and NPV of the 16S rDNA PCR (F. nucleatum detection) were 97.6, 89.4, 88.9 and 97.7%, respectively, whilst the respective values for the rpoB PCR (F. necrophorumdetection) were 100.0, 97.4, 83.3 and 100.0%, as compared to culture. In conclusion, PCR proved of higher diagnostic yield than culture and detected both species in culture-negative specimens. As similar results have been obtained for other anaerobic species, the golden standard anaerobic culture seems to be insufficient for detecting Fusobacterium spp. in the area of molecular microbiology and needs further re-evaluation.