[Case report: positive signals from automated blood-culture system with negative direct Gram examination]

Detection of positive haemoculture is usually managed by an automated system. When a bottle is detected positive but that the Gram coloration does not reveal germs by direct examination, transfer onto chocolate blood agar generally allows to confirm or infirm bacteraemia. In light of a case of Fusobacterium nucleatum bacteraemia, we discuss the opportunity of pairing it with an enrichment broth. M. N, hospitalized in the hepatogastroenterology department, runs a fever of undetermined origin. Three pairs of blood samples are collected on May 7th, 2004, another pair on May 9th, 2004 and a last pair on May 10th, 2004. They are incubated in a Bactec 9120 analyzer. A positive signal is detected in the two last anaerobic haemocultures pairs after four days of incubation, but in both cases, the Gram coloration does not bring germs to light. A systematic transfer of the broth onto chocolate blood agar with incubation under CO2 enriched atmosphere and anaerobiosis is carried out. After 24 hours, the solid media remain sterile. The samples found positive by the Bactec(TM) are then transferred onto Schaedler broth in order to favour a potential growth of fastidious germs. The culture will prove to be positive only in this enrichment medium, allowing the identification of F. nucleatum. An hepatic abscess will then be revealed in the patient. It thus appears judicious to associate an enrichment medium with transplanted solid medium when the context is evocative of a real infection (clinic, positivity delays...).