Quantitative Molecular Test Improves Diagnosis of Brucellosis

Rapid diagnosis of individuals infected with brucellosis can sometimes be difficult with conventional microbiological techniques.

The diagnostic yield of a real-time polymerase chain reaction (rt-PCR) assay during an outbreak of brucellosis supported the rapid identification of the causative organism.

Microbiologists at the Carlos Haya University Hospital (Malaga, Spain) compared the rt-PCR with conventional microbiological methods for diagnosing brucellosis in a family outbreak of brucellosis due to consumption of unpasteurized goat cheese. Two blood culture sets, a quantitative rt- PCR assay in serum, Rose Bengal test, standard agglutination test (SAT), and immunocapture–agglutination test were performed for all the patients with suspected Brucella infection. In patients exposed but asymptomatic, only serology and real-time PCR were performed.

Blood cultures were positive in three of the eight symptomatic cases and all of them identified as Brucella melitensis biovar 3. The Rose Bengal test result was positive in seven of the symptomatic subjects. SAT and the immunocapture-agglutination test result had titers within the diagnostic range for six patients. SAT and the immunocapture–agglutination test results were positive but showed titers below the diagnostic range in the remaining two cases and in both asymptomatic subjects.

The PCR amplifications were performed in capillary tubes with a LightCycler instrument (Roche Diagnostic; San Cugat del Valles, Spain) using primers obtained from Tib-Molbiol (Berlin, Germany). Each assay was performed using a standard curve of genomic B. melitensis DNA (2 × 105 genome copies per 2 mL DNA extract) and negative controls (water). The rt-PCR was positive in all subjects who became ill and negative in those who did not develop symptoms.

The authors concluded that quantitative rt-PCR could be a useful tool for the rapid diagnosis of persons involved in outbreaks of brucellosis due to occasional consumption of unpasteurized milk or cheese. However, it is possible that this technology will have no practical use for handling outbreaks in occupationally exposed subjects, and studies are needed to determine its usefulness in outbreaks affecting laboratory workers. The study was published in the November 2011 edition of the journal Diagnostic Microbiology and Infectious Disease.

Related Links:
Carlos Haya University Hospital
Roche Diagnostic
Tib-Molbiol