Human infection may be caused by several species of the genus Brucella. These organisms are fastidious, slow-growing gram-negative bacilli capable of producing severe localized and systemic infection. Infections have typically been acquired by zoonotic transmission, primarily related to livestock and dairy industries. There is great concern regarding the use of this organism for a bioterror-related attack. The organism is easily transmissible, so it is critical that the laboratory be informed whenever brucellosis is suspected.
Use
This culture is used to isolate Brucella species from clinical specimens. Because of the risk of laboratory-acquired infection and because isolation of Brucella species may represent a sentinel event in a bioterror attack, most clinical microbiology laboratories limit the workup of suspected isolates to simple tests to rule out suspicious colonies, referring isolates that fail to "rule out " � to their local public health laboratory for identification and further characterization. Final results for testing, therefore, may be delayed compared to common bacterial isolates.
Method: Specimens are inoculated onto a blood agar (such as Brucella blood agar), chocolate agar, and Thayer-Martin agar (if contamination with endogenous flora is suspected). Specimens for Brucella are also inoculated onto MacConkey agar.
Turnaround time: Isolation and preliminary identification for routine cultures are usually available in 3 " �7 days. Additional time is required for transfer to the local public health laboratory, confirmation of identification, and further testing.
Special Collection and Transport Instructions
The organisms primarily infect the reticuloendothelial system, so bone marrow and blood are the specimens of choice for patient evaluation. Specimens from other infected tissue or sites should also be submitted for culture. Serologic testing is recommended for diagnosis in patients with suspected brucellosis.
Interpretation
Expected results: Negative.
Positive: Isolation of Brucella in culture is diagnostic for brucellosis.
Limitations
Brucella may be difficult to detect by Gram stain in primary specimens.
Common pitfalls: Because brucellosis may present after a prolonged incubation period, or present with nonspecific symptoms and an indolent onset, the diagnosis may not be considered until progression into the chronic phase of illness. Clinicians may fail to request specific cultures for brucellosis, or alert the laboratory of their clinical suspicion.
Other Considerations
Brucellosis is a reportable disease. Patients with a diagnosis of brucellosis must be reported to the local department of health.