Approach Considerations
The laboratory should be alerted when a diagnosis of glanders or melioidosis is suspected. Some automated culture systems may misidentify Burkholderia pseudomallei as Pseudomonas spp. [6] Although clinical diagnostic laboratories functioning at Biosafety Level 2 (BSL-2) may isolate B pseudomallei and B mallei from patient specimens, once B pseudomallei or B mallei is suspected, work should be transferred to a BSL-3 facility. [19, 16]
In patients with glanders, imaging may reveal abscesses in the lungs, liver, and spleen. Serologic testing for diagnosis of glanders is largely experimental. [2]
Laboratory Studies
Basic laboratory tests include complete blood cell count (CBC) and liver function studies. The CBC may reveal a mild leukocytosis with a left shift or leukopenia. With glanders, the white blood cell count (WBC) is often normal or minimally elevated. Elevated liver enzyme levels in glanders may signify hepatic abscess formation. In melioidosis specifically, laboratory studies may demonstrate anemia, leukocytosis, hepatic impairment, renal insufficiency, and coagulopathy.
Microbiology
Gram stain may reveal small, gram-negative bacilli, which stain irregularly with methylene blue or Wright stain, and they may demonstrate a safety pin bipolar appearance. The organisms can be cultured from abscesses, secretions, sputum, blood and urine with standard media. Primary isolation requires 48 to 72 hours. Another useful culture medium for isolation of B pseudomallei from non-sterile sites (sputum, pharynx swabs) is Ashdown's selective medium. [6]
Blood culture results for B mallei are often negative, while blood cultures for B pseudomallei often positive and positive urine cultures can indicate prostatitis or renal abscesses. In septicemic melioidosis, blood culture results may be negative until just before death. Meat nutrient agar or the addition of 1-5% glucose may accelerate growth of bacteria.
Polymerase chain reaction (PCR) assays are rapid and spedific but may be less sensitive than cultures.
Methods for detecting and differentiating the B pseudomallei complex has been under investigation due to phenotypic and genotypic similarities of these species. Although B thailandensis and B oklahomensis are generally avirulent, both display phenotypic characteristics similar to that of B pseudomallei. Real-time PCR assays have been developed but require multiple real-time PCR reactions in order to correctly identify B pseudomallei, B mallei, and B thailandensis. A multiplex PCR assay is under development that can specifically detect and differentiate among B mallei, B pseudomallei, and B thailandensis in a single-tube format. [4, 5, 21]
Serologic tests
Serologic tests are of limited value, particularly in endemic areas where seroprevalence is high. Indirect hemagglutination tests are the most frequently used serologic assay in endemic regions but are poorly standardized.
For B mallei, agglutination test results may be positive after 7-10 days, but a high background titer found in normal sera makes interpretation difficult. Complement fixation (CF) tests are more specific, but less sensitive, and may require 40 days for conversion. CF is considered positive if the titer is 1:20 or greater. A 4-fold increase in the titer supports the diagnosis of B pseudomallei infection. [6]
Imaging Studies
Chest radiography may demonstrate bilateral bronchopneumonia, miliary nodules, segmental or lobar infiltrates, and cavitating lesions. With melioidosis, an abnormal chest radiography finding is present in up to 80% of patients (usually diffuse nodular shadowing). [4]
Abdominal and pelvic ultrasound, CT or MRI may reveal abscesses in the spleen, liver and/or prostate. [20]
Bone and soft tissue musculoskeletal involvement may be seen with plain radiographs and magnetic resonance imaging. These findings are consistent with disseminated melioidosis. [20]
