We analyzed the extracellular proteome of colistin-resistant Korean Acinetobacter baumannii (KAB) strains to identify proteome profiles that can be used to characterize extensively drug-resistant KAB strains. Four colistin-resistant KAB strains with colistin resistance associated with point mutations in pmrB and pmrC genes were analyzed. Analysis of the extracellular proteome of these strains revealed the presence of 506 induced common proteins, which were hence considered as the core extracellular proteome. Class C ADC-30 and class D OXA-23 β-lactamases were abundantly induced in these strains. Porins (CarO and CarO-like porin), outer membrane proteins (OmpH and BamABDE), transport protein (AdeK), receptor (TonB), and several proteins of unknown function were among the specifically induced proteins. Based on the sequence homology analysis of proteins from the core proteome and those of other A. baumannii strains and pathogenic bacterial species as well as further in silico screening, we propose that CarO-like porin is an A. baumannii-specific protein and that two tryptic peptides that originate from CarO-like porin detected by tandem mass spectrometry are peptide makers of this protein.
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