Identification of strains that express a -like capsular polysaccharide.

and are Gram-negative, soil-dwelling bacteria that are found in a wide variety of environmental niches. While is the causative agent of melioidosis in humans and animals, members of the complex typically only cause disease in immunocompromised hosts. In this study, we report the identification of strains isolated from either patients or soil in Laos and Thailand that express a -like 6-deoxyheptan capsular polysaccharide (CPS). These 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 sequencing confirmed the identity of these isolates as (formerly genomovar I). Total carbohydrates extracted from cell pellets reacted with CPS-specific mAbs MCA147, 3C5, and 4C4, but did not react with the lipopolysaccharide-specific mAb Pp-PS-W. Whole genome sequencing of the isolates revealed the presence of genes demonstrating significant homology to those comprising the CPS biosynthetic gene cluster. Collectively, our results provide compelling evidence that strains expressing the same CPS as co-exist in the environment alongside . Since CPS is a target that is often used for presumptive identification of , it is possible that the occurrence of these unique strains may complicate the diagnosis of melioidosis.IMPORTANCE, the etiologic agent of melioidosis, is an important cause of morbidity and mortality in tropical and subtropical regions worldwide. The 6-deoxyheptan capsular polysaccharide (CPS) expressed by this bacterial pathogen is a promising target antigen that is useful for rapidly diagnosing melioidosis. Using assays incorporating CPS-specific monoclonal antibodies, we identified both clinical and environmental isolates of that express the same CPS antigen as . Because of this, it is important that staff working in melioidosis-endemic areas are aware that these strains co-exist in the same niches as and do not solely rely on CPS-based assays such as latex-agglutination, AMD Plus Rapid Tests, or immunofluorescence tests for the definitive identification of isolates.