Brucella suis Bacteremia Misidentified as Ochrobactrum antropii by Vytek 2 Automated System
Methods: On January 2013 a 67-year-old man was admitted to our institution with a 3-day history of fever up to 39°C and fatigue. His medical history was significant for mitral valve replacement in 2010. The patient had close contact with pigs by keeping them as pets at home. On the day of admission two sets of aerobic blood cultures (BC) were obtained, becoming positive after 72 hs of incubation. The isolated organism was a non-motile gram-negative coccobacillus identified as O. anthropi by Vytek 2 system. In order to establish the clinical significance of this isolation in the setting of a work up for possible prosthetic infective endocarditis (IE), repeated BC were taken on days 3 and 5 of admission, all of them resulting positive for the same organism. No vegetations were seen in the transesophageal echocardiogram. A diagnosis of definite IE was made based on the presence of 2 major criteria (six positive BC taken >12 hs apart, plus 6/6 positive BC) and 2 minor criteria (predisposing cardiac condition and fever > 38°C).
Results: Due to the rareness of the isolated pathogen, the adverse clinical outcome while on treatment for O. antropii, and the strong epidemiological data, patient’s serum was tested for the presence of Brucella antibodies with microagglutination test, complement fixation test and enzyme linked immune-sorbent assay (ELISA) confirming the diagnosis of acute brucellosis. BC bottles were sent to a reference laboratory where the isolates were identified as B. suis biovar 1 by Polymerase Chain Reaction-Restriction Fragment Length Polymorphism, thus confirming the misidentification of B. suis as O. antropii by Vytek 2.
Conclusion: B. suis can be misidentified using Vytek 2 system. Previous reports have described erroneous identification of Brucella spp. by API 20NE, RapID NF Plus and MicroScan systems. Countries where brucellosis is endemic need to be aware of this possibility. A high index of suspicion based on epidemiological and clinical data is essential not only to make accurate diagnosis and provide adequate treatment but also because Brucella spp. requires special handling to prevent unintentional exposure.
M. C. Dignani, None
N. Lucero, None
A. Vicente, None
R. Galaguza, None
G. Vera Bello, None
H. Pagella, None