Deciphering tissue-induced Klebsiella pneumoniae lipid A structure.

Enrique Llobet, Verónica Martínez-Moliner, David Moranta, Käthe M Dahlström, Verónica Regueiro, Anna Tomás, Victoria Cano, Camino Pérez-Gutiérrez, Christian G Frank, Helena Fernández-Carrasco, José Luis Insua, Tiina A Salminen, Junkal Garmendia, José A Bengoechea

Index: Proc. Natl. Acad. Sci. U. S. A. 112 , E6369-78, (2015)

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Abstract

The outcome of an infection depends on host recognition of the pathogen, hence leading to the activation of signaling pathways controlling defense responses. A long-held belief is that the modification of the lipid A moiety of the lipopolysaccharide could help Gram-negative pathogens to evade innate immunity. However, direct evidence that this happens in vivo is lacking. Here we report the lipid A expressed in the tissues of infected mice by the human pathogen Klebsiella pneumoniae. Our findings demonstrate that Klebsiella remodels its lipid A in a tissue-dependent manner. Lipid A species found in the lungs are consistent with a 2-hydroxyacyl-modified lipid A dependent on the PhoPQ-regulated oxygenase LpxO. The in vivo lipid A pattern is lost in minimally passaged bacteria isolated from the tissues. LpxO-dependent modification reduces the activation of inflammatory responses and mediates resistance to antimicrobial peptides. An lpxO mutant is attenuated in vivo thereby highlighting the importance of this lipid A modification in Klebsiella infection biology. Colistin, one of the last options to treat multidrug-resistant Klebsiella infections, triggers the in vivo lipid A pattern. Moreover, colistin-resistant isolates already express the in vivo lipid A pattern. In these isolates, LpxO-dependent lipid A modification mediates resistance to colistin. Deciphering the lipid A expressed in vivo opens the possibility of designing novel therapeutics targeting the enzymes responsible for the in vivo lipid A pattern.