ramR Mutations in Clinical Isolates of Klebsiella pneumoniae with Reduced Susceptibility to Tigecycline

Abstract

ABSTRACT Five Klebsiella pneumoniae isolates with reduced susceptibility to tigecycline (MIC, 2 μg/ml) were analyzed. A gene homologous to ramR of Salmonella enterica was identified in Klebsiella pneumoniae . Sequencing of ramR in the nonsusceptible Klebsiella strains revealed deletions, insertions, and point mutations. Transformation of mutants with wild-type ramR genes, but not with mutant ramR genes, restored susceptibility to tigecycline and repressed overexpression of ramA and acrB . Thus, this study reveals a molecular mechanism for tigecycline resistance in Klebsiella pneumoniae .