Characterization of Klebsiella pneumoniae strains Exposed to Subinhibitory Concentrations of Chlorhexidine

Abstract

Chlorhexidine, a topical antiseptic, acts as a cationic biguanide altering the osmotic transport of the bacterial cell wall that has been used throughout the world to prevent healthcare-associated infections for decades. The routine application of chlorhexidine can result in decreased susceptibility of bacteria over time. The aim of this study was to develop Klebsiella pneumoniae strains after exposure to chlorhexidine and characterize these adapted strains in terms of their virulence ability both by in vivo and in vitro methods. Two clinical strains of K.pneumoniae were included in the study. One strain was completely susceptible and the other was resistant to certain antibiotics. Susceptible strain was subjected in the exposure assay as parent/wild strain. Exposure was performed by increasing chlorhexidine concentrations in agar plates. Chlorhexidine concentrations were gradually decreased reaching a final concentration of 0.12 mg/L after five weeks. Chlorhexidine-adapted viable colonies were selected and isolated. Minimal inhibitor concentrations of chlorhexidine, sodium hypochloride, benzalkonium chloride and triclosan for K.pneumoniae strains were determined using broth microdilution method. Reverse transcription-polymerase chain reaction analysis were performed for efflux pumps named cepA, kdeA and acrKp expressions. Fluorimetric efflux assay by using Rhodamine 6G was performed. Galleria mellonella killing assay and in vitro virulence determinants such as esculin hydrolysis, biofilm production, lecithinase, DNase activity, hemolytic activity, lipase production, mucoviscocity, casein hydrolysis and complement-mediated serum killing were evaluated. K.pneumoniae strains exposed to chlorhexidine did not show any antibiotic resistance. MICs for chlorhexidine, sodium hypochloride, and benzalkonium chloride were increased in the adapted strain. Efflux pumps of cepA and kdeA were over-expressed in the chlorhexidine adapted strain. Rhodamine 6G assay showed an increased efflux in the adapted strain. G.mellonella killing assay showed median virulence score. All strains, were esculin positive, while biofilm production, lecithinase, DNase, hemolytic activity, lipase production, mucoviscocity, casein hydrolysis were all negative. The susceptible parent/wild strain was susceptible to the complement-mediated serum killing, while the chlorhexidine adapted strain showed intermediate susceptibility. Chlorhexidine adapted strains of K.pneumoniae showed increased efflux pump expression, enhanced G.mellonella killing and raised resistance to serum killing. No difference was determined for other determinants. Minimal correlation was found between chlorhexidine resistance and virulence in K.pneumoniae.