Multiple mutations in lipid-A modification pathway & novel fosA variants in colistin-resistant Klebsiella pneumoniae

AIM: To investigate antimicrobial resistance mechanisms in a cluster of colistin-resistant Klebsiella pneumoniae. METHODS: Antimicrobial susceptibility was tested by disk diffusion and broth microdilution. Whole-genome sequencing and genome analysis were performed. RESULTS: The eight colistin-resistant K. pneumoniae isolates belonged to three different clones (ST11, 14 and 231). The eptA and arnT genes from lipid modification pathway had novel (R157S in arnT and Q319R in eptA) and rare mutations (V39L, R152H, S260L and A279G in eptA). Several substitutions were also identified in mgrB, pmrB, phoP and phoQ genes. The mcr genes were absent in all isolates. Isolates had variants from existing classes of fosA gene. CONCLUSION: Complex combination of mutations might have led to colistin resistance, which suggests that continuous surveillance of molecular mechanisms is required.