Lipopolysaccharide from nonvirulent Ara+ Burkholderia pseudomallei isolates is immunologically indistinguishable from lipopolysaccharide from virulent Ara- clinical isolates

Abstract

Different lines of evidence suggest that a discrepancy between the distribution of Burkholderia (Pseudomonas) pseudomallei in the environment and the distribution of the disease melioidosis is attributable, at least in part, to phenotypic differences between clinical and some environmental isolates. Two antigenically and biochemically distinct biotypes have been described, only one of which is virulent. In this study, lipopolysaccharides (LPSs) were extracted by the proteinase K digestion method from a total of 214 B. pseudomallei isolates, and their immunoreactivities with sera from patients with different clinical spectra and with other infections were evaluated. With the exception of4 isolates from a total of 214 tested, the sodium dodecyl sulfate-polyacrylamide gel electrophoresis silver-staining profiles of the LPSs from the two biotypes showed identical ladder patterns that were typical for smooth LPSs from other gram-negative bacteria. The 210 isolates with typical LPS patterns (119 Ara- clinical, 13 Ara- soil, 70 Ara+ soil, and 8 reference National Type Culture Collection strains) also exhibited similar immunoblot profiles against pooled sera from patients with melioidosis and hyperimmune mouse sera. Concordant findings were noted in the indirect enzyme-linked immunosorbent assay with Ara- and Ara+ LPSs to coat the microtiter plates. The LPSs of the different B. pseudomallei biotypes appear antigenically indistinguishable. It is, therefore, unlikely that this component is related to the virulence and pathogenicity of B. pseudomallei.

FIG. 1

Representative typical silver-stained SDS-PAGE profiles of LPSs extracted from 214 Ara⁻ and Ara⁺ B. pseudomallei isolates. Lanes: 1 and 2, Ara⁻ clinical isolates; 3 and 4, Ara⁻ soil isolates; 5 to 8, Ara⁺ soil isolates. Numbers on the left are molecular weight markers (in thousands).

FIG. 2

Atypical silver-stained SDS-PAGE profiles of LPSs extracted from two clinical Ara⁻ isolates (lanes 2 and 3). A representative pattern of typical B. pseudomallei isolates is shown for comparison (lane 1). Numbers on the left are molecular weight markers (in thousands).

FIG. 3

Representative immunoblot profiles of LPSs from Ara⁻ and Ara⁺ B. pseudomallei isolates against sera pooled from patients with culture-proven melioidosis. The serum was used at a 1:7,000 dilution. Lanes: 1 and 2, Ara⁻ clinical isolates; 3 and 4, Ara⁻ soil isolates; 5 to 8, Ara⁺ soil isolates. Numbers on the left are molecular weight markers (in thousands).

FIG. 4

Representative immunoblot profiles of LPSs from Ara⁻ and Ara⁺ B. pseudomallei isolates against immune mouse serum. The serum was used at a dilution of 1:500. Lanes: 1 and 2, Ara⁻ clinical isolates; 3 and 4, Ara⁻ soil isolates; 5 to 8, Ara⁺ soil isolates. Numbers on the left are molecular weight markers (in thousands).

FIG. 5

Immunoreactivities of LPSs from the Ara⁺ biotype. Sera were from patients with septicemic melioidosis (lanes 1 to 3), melioidosis patients with localized infections (lanes 4 to 6), and patients with other infections caused by gram-negative organisms (lanes 7 to 9) and from normal individuals from areas where infection is endemic (lanes 10 to 12) and nonendemic (lanes 13 to 15). All sera were used at a 1:7,000 dilution. Numbers on the left are molecular weight markers (in thousands).

FIG. 6

Immunoreactivities of pooled LPS extracted from Ara⁻ B. pseudomallei. See legend to Fig. 5 for details.