['Klebsiella pneumoniae has become the predominant pathogen causing primary pyogenic liver abscess (PLA).', 'K. pneumoniae was stimulated by human serum, and gene expression was analyzed by microarray.', 'Three putative iron acquisition systems, Yersinia high-pathogenicity island (HPI), iucABCDiutA, and iroA(iroNDCB), that increased in expression and predominated in PLA-associated K. pneumoniae strains were identified. By use of siderophore uptake assays, these 3 systems were confirmed to be siderophore-dependent iron acquisition systems. Only the irp2-iuc-iroA triple mutant showed decreased virulence in mice. Full-genome analysis of K. pneumoniae strain NTUH-K2044 identified 10 putative iron uptake systems. Seven of these 10 systems were TonB dependent, including Yersinia HPI, iucABCDiutA, and iroA. A tonB deletion mutant was demonstrated to have profound attenuation of virulence. Immunization with the tonB mutant resulted in seroconversion of extracellular polysaccharide antibodies and protective efficacy against subsequent exposure to the parental strain.'] Do serum-induced iron-acquisition systems and TonB contribute to virulence in Klebsiella pneumoniae causing primary pyogenic liver abscess?