KpnEF, a New Member of the Klebsiella pneumoniae Cell Envelope Stress Response Regulon, Is an SMR-Type Efflux Pump Involved in Broad-Spectrum Antimicrobial Resistance

Abstract

ABSTRACTKlebsiella pneumoniaehas been frequently associated with nosocomial infections. Efflux systems are ubiquitous transporters that also function in drug resistance. Genome analysis ofK. pneumoniaestrain NTUH-K2044 revealed the presence of ∼15 putative drug efflux systems. We discuss here for the first time the characterization of a putative SMR-type efflux pump, anebrABhomolog (denoted here askpnEF) with respect toKlebsiellaphysiology and the multidrug-resistant phenotype. Analysis of hypermucoviscosity revealed direct involvement ofkpnEFin capsule synthesis. The ΔkpnEFmutant displayed higher sensitivity to hyperosmotic (∼2.8-fold) and high bile (∼4.0-fold) concentrations. Mutation inkpnEFresulted in increased susceptibility to cefepime, ceftriaxone, colistin, erythromycin, rifampin, tetracycline, and streptomycin; mutated strains changed from being resistant to being susceptible, and the resistance was restored upon complementation. The ΔkpnEFmutant displayed enhanced sensitivity toward structurally related compounds such as sodium dodecyl sulfate, deoxycholate, and dyes, including clinically relevant disinfectants such as benzalkonium chloride, chlorhexidine, and triclosan. The prevalence ofkpnEFin clinical strains broadens the diversity of antibiotic resistance inK. pneumoniae. Experimental evidence of CpxR binding to the efflux pump promoter and quantification of its expression in acpxARmutant background demonstratedkpnEFto be a member of the Cpx regulon. This study helps to elucidate the unprecedented biological functions of the SMR-type efflux pump inKlebsiellaspp.