Tigecycline Resistance Can Occur Independently of the ramA Gene in Klebsiella pneumoniae

Tigecycline resistance in Klebsiella pneumoniae results from ramA upregulation that causes the overexpression of the efflux pump, AcrAB-TolC. Tigecycline mutants, derived from Ecl8Δ ramA , can exhibit a multidrug resistance phenotype due to increased transcription of the marA , rarA , acrAB , and oqxAB genes. These findings support the idea that tigecycline or multidrug resistance in K. pneumoniae , first, is not solely dependent on the ramA gene, and second, can arise via alternative regulatory pathways in K. pneumoniae .