Burkholderia pseudomallei and Burkholderia cepacia are Gram-negative,
soil-dwelling bacteria that are found in a wide variety of environmental niches. While
B. pseudomallei is the causative agent of melioidosis in humans and animals, members
of the B. cepacia complex typically only cause disease in immunocompromised hosts. In
this study, we report the identification of B. cepacia strains isolated from either patients
or soil in Laos and Thailand that express a B. pseudomallei-like 6-deoxyheptan capsular
polysaccharide (CPS). These B. cepacia strains were initially identified based on their
positive reactivity in a latex agglutination assay that uses the CPS-specific monoclonal
antibody (mAb) 4B11. Mass spectrometry and recA sequencing confirmed the identity
of these isolates as B. cepacia (formerly genomovar I). Total carbohydrates extracted
from B. cepacia cell pellets reacted with B. pseudomallei CPS-specific mAbs MCA147, 3C5,
and 4C4, but did not react with the B. pseudomallei lipopolysaccharide-specific mAb
Pp-PS-W. Whole genome sequencing of the B. cepacia isolates revealed the presence of
genes demonstrating significant homology to those comprising the B. pseudomallei CPS
biosynthetic gene cluster. Collectively, our results provide compelling evidence that B.
cepacia strains expressing the same CPS as B. pseudomallei co-exist in the environment
alongside B. pseudomallei. Since CPS is a target that is often used for presumptive
identification of B. pseudomallei, it is possible that the occurrence of these unique B.
cepacia strains may complicate the diagnosis of melioidosis
