Laboratory and clinical Pseudomonas aeruginosa strains do not bind glycosphingolipids in vitro or during type IV pili-mediated initial host cell attachment

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Abstract
The glycosphingolipids (GSLs) gangliotriaosylceramide (Gg3) and gangliotetraosylceramide (Gg4) have been implicated as receptors for type IV pili (T4P)-mediatedPseudomonas aeruginosaepithelial cell attachment. SinceP. aeruginosaT4P are divided into five groups, the authors determined whether GSLs in general, and Gg3and Gg4in particular, are specifically bound and required for host epithelial cell attachment of clinical and laboratory strains within these groups. An enterohaemorrhagicEscherichia colistrain, CL56, known to bind to both Gg3and Gg4, provided a positive control. TLC overlay showed no binding of more than 12P. aeruginosastrains to either Gg3or Gg4(or other GSLs), while CL56 Gg3/Gg4binding was readily detectable. GSL ELISA similarly demonstrated no significantP. aeruginosabinding to Gg3or Gg4, compared with CL56. Using a selective chemical inhibitor, epithelial cell GSL synthesis was abrogated, and Gg3and Gg4expression deleted, butP. aeruginosaattachment was not impaired. Target cell attachment was mediated by T4P, since non-piliated, but flagellated, mutants were unable to bind to the target cells. CFTR (cystic fibrosis transmembrane conductance regulator) has also been implicated as a receptor; however, in this work, overexpression of CFTR had no effect onP. aeruginosabinding. It is concluded that neither Gg3nor Gg4are specifically recognized byP. aeruginosa, and that endogenous GSLs do not have a role in the attachment of live intactP. aeruginosato cultured lung epithelial cells. In contrast to whole piliatedP. aeruginosa, T4P sheared from such bacteria showed significant Gg3and Gg4binding, which may explain the results of other studies.