Lipopolysaccharide glycotyping of clarithromycin-resistant and clarithromycin-susceptible Canadian isolates of Helicobacter pylori

Lipopolysaccharide (LPS) of Helicobacter pylori exhibits several unique structures, such as Lewis (Le) antigens, alpha-1,6-glucan, and DD-heptan. To investigate the relationship between LPS structure and resistance to clarithromycin, 41 Canadian isolates of H. pylori were characterized by whole-cell ELISA (enzyme-linked immunosorbent assay), sugar analysis, immunoblotting, and indirect immunofluorescence. The expression of type 2 Lewis X and (or) Lewis Y antigens was detected in 22 of 23 (95.7%) clarithromycin-resistant and in 14 of 18 (77.7%) clarithromycin-susceptible H. pylori strains (P < 0.05), and 8 isolates co-expressed type 1 and type 2 Le antigens (8/41, 19.5%). A significantly higher frequency of alpha-1,6-glucan (P < 0.01) was detected in clarithromycin-resistant strains than in clarithromycin-susceptible strains (19/23 (82.6%) versus 11/18 (61.1%)). Sugar analysis of selected alpha-1,6-glucan-positive H. pylori strains confirmed that they frequently contained elevated amounts of DD-heptose. Clarithromycin-resistant isolates were also characterized by low expression levels or absence of CagA (17/23, 73.9%). Indirect immunofluorescence studies carried out on selected H. pylori strains with rabbit immune sera specific for alpha-1,6-glucan confirmed broad recognition of alpha-1,6-glucan epitope. The binding was not affected by LPS glycotype of H. pylori isolates examined nor by their CagA status or resistance to clarithromycin. These findings suggest alpha-1,6-glucan as a potential vaccine target, especially in an era of increasing clarithromycin resistance in H. pylori.