Bradshaw, J.; Sanchez-Garrido, J.; Berkachy, R.; Rattle, J.; Preston, C.; Pizza, M.; Ros, I. M.; Romano, M. R.; Wong, J.; Frankel, G.

The conserved bacterial polysaccharide Poly-N-Acetyl-Glucosamine (PNAG) is a potential broad-spectrum vaccine candidate. While the immunogenicity of PNAG-based vaccine candidates has been established, characterisation of PNAG production across clinically relevant bacteria remains largely unknown. In particular, PNAG production in the Gram-negative pathogen Klebsiella pneumoniae (KP) is not well understood. Here, we demonstrate that PNAG production is prevalent in clinical KP isolates, where it is secreted as extracellular networks during adherent growth conditions. However, during severe KP pulmonary infection, KP PNAG production undergoes a switch to a cell-associated phenotype, coating the bacterial cell surface. By screening a panel of isogenic KP mutants in prominent cell surface components (delta wcaJ, delta rmpADC, delta rfb, delta ompA and delta ompk36), we identified KP capsular polysaccharide as a key determinant underpinning the phenotype. Deleting genes involved in capsule synthesis (delta wcaJ) and regulation (delta rmpADC) resulted in cell-associated PNAG during adherent growth and infection of alveolar epithelial cells in vitro. Taken together, we describe a novel interaction between KP surface polysaccharides and detect for the first time, cell-associated PNAG in KP during lung infection, highlighting PNAG as an attractive KP vaccine antigen.