Seronegative bacteremic melioidosis caused by Burkholderia pseudomallei with ambiguous biochemical profile: clinical importance of accurate identification by 16S rRNA gene and groEL gene sequencing.

An aerobic gram-negative bacterium was isolated from the blood and sputum of an 84-year-old, chair-bound nursing home resident with acute bacteremic pneumonia. Although the phenotypic characteristics suggested that the bacterium could be Burkholderia pseudomallei, the Vitek 1 system (GNI+), which can successfully identify 99% of B. pseudomallei strains, showed that the bacterium was "unidentified." Immunoglobulin G against the lipopolysaccharide (LPS) of B. pseudomallei, as detected by an LPS-based enzyme-linked immunosorbent assay with 95% sensitivity, was negative in both the acute-phase and convalescent-phase sera. Sequencing of the groEL gene showed that the isolate was B. pseudomallei. Proper identification of the bacterium in this study is crucial, since there would be a radical difference in the duration of antimicrobial therapy.