Immunoproteomic profiling identifies a type 1 fimbrial antigen in clinical isolates of Klebsiella pneumoniae.

Klebsiella pneumoniae is a Gram-negative, encapsulated, facultative anaerobic bacillus responsible for healthcare-associated infections and is classified by the World Health Organization as a critical priority pathogen due to the increasing prevalence of hypervirulent and multidrug-resistant strains. The aim of this study was to identify K. pneumoniae antigens involved in host-pathogen interactions using proteomic and immunoproteomic approaches in two clinical isolates (Kp1 and Kp6) and one reference strain (ATCC 13883). The analysis enabled the identification of 158 unique proteins, 66 of which (41.8%) exhibited immunoreactivity. An antigenic spot designated as p18 (18kDa, pI 5.1) was selected and sequenced by liquid chromatography-mass spectrometry (LC-MS), yielding two peptides (AAVAFLGTAIDSAHPK and YYAIGEATPGAANADATFK) that collectively covered 22.52% of the Escherichia coli type 1 fimbrial adhesin, with 100% sequence homology. These findings constitute the first proteomic evidence identifying type 1 fimbriae in K. pneumoniae, a protein associated with adhesion and immune evasion among enterobacteria.