Molecular mechanism of colistin resistance in Klebsiella pneumoniae

Objective To investigate the molecular mechanism of colistin resistance in Klebsiella pneumoniae (K.pneumoniae). Methods Three clinical isolates of colistin-resistant K. pneumoniae (FK1149, FK1920 and FK1934) and three colistin-resistant mutants (FK660R, FK713R and FK729R) were investigated. Resistance genes of pmrAB, phoPQ, mgrB, crrAB, mcr-1 and mcr-2 were detected by PCR and then analyzed by sequencing. PROVEAN platform was used to predict changes in the biological functions of proteins related to drug resistance. Expression of pmrH, pmrC, mgrB and phoP genes was measured using quantitative real-time PCR. LPS silver staining and conjugation assay were performed to analyze the three clinical colistin-resistant isolates. Results Amino acid substitutions in PmrA (G53V), PmrB (T157P, R256G), MgrB (F44C) and CrrB (E189K) were detected. ISkpn14 and IS5-like insertion sequences were detected in FK713R and FK729R, respectively. FK1149, FK1920 and FK1934 were negative for mcr genes. Compared with the wild-type strain, expression of pmrH and pmrC genes at the transcriptional level was increased in all investigated isolates. Changes in the expression of phoP and mgrB genes were also observed. A partial deletion of LPS was identified in FK1149. Conclusion LPS modification induced by inactivation of PmrAB or MgrB is the main molecular mechanism of colistin resistance in K. pneumoniae isolates in this study. Mutations in PmrA (G53V), MgrB (F44C) and CrrB (E189K) that might be related to colistin resistance are detected for the first time in clinical isolates of K. pneumoniae. Key words: Colistin; Klebsiella pneumoniae; Drug resistance mechanism; Two-component regulatory system