Mechanisms of Tolerance and Resistance to Chlorhexidine in Clinical Strains of <i>Klebsiella pneumoniae</i> Producers of Carbapenemase: Role of New Type II Toxin-Antitoxin System, PemIK

• Main Authors: Ines Bleriot, Lucia Blasco, Mercedes Delgado-Valverde, Ana Gual de Torella, Anton Ambroa, Laura Fernandez-Garcia, Maria Lopez, Jesus Oteo-Iglesias, Thomas K. Wood, Alvaro Pascual, German Bou, Felipe Fernandez-Cuenca, Maria Tomas
• Format: Article
• Language: English
• Published: MDPI AG 2020-09-01
• Series: Toxins
• Subjects: tolerance; persistence; cross-resistance; toxin-antitoxin system; PemI/PemK; <i>Klebsiella pneumoniae</i>
• Online Access: https://www.mdpi.com/2072-6651/12/9/566

Although the failure of antibiotic treatment is normally attributed to resistance, tolerance and persistence display a significant role in the lack of response to antibiotics. Due to the fact that several nosocomial pathogens show a high level of tolerance and/or resistance to chlorhexidine, in this study we analyzed the molecular mechanisms associated with chlorhexidine adaptation in two clinical strains of <i>Klebsiella pneumoniae</i> by phenotypic and transcriptomic studies. These two strains belong to ST258-KPC3 (high-risk clone carrying β-lactamase KPC3) and ST846-OXA48 (low-risk clone carrying β-lactamase OXA48). Our results showed that the <i>K. pneumoniae</i> ST258-KPC3CA and ST846-OXA48CA strains exhibited a different behavior under chlorhexidine (CHLX) pressure, adapting to this biocide through resistance and tolerance mechanisms, respectively. Furthermore, the appearance of cross-resistance to colistin was observed in the ST846-OXA48CA strain (tolerant to CHLX), using the broth microdilution method. Interestingly, this ST846-OXA48CA isolate contained a plasmid that encodes a novel type II toxin/antitoxin (TA) system, PemI/PemK. We characterized this PemI/PemK TA system by cloning both genes into the IPTG-inducible pCA24N plasmid, and found their role in persistence and biofilm formation. Accordingly, the ST846-OXA48CA strain showed a persistence biphasic curve in the presence of a chlorhexidine-imipenem combination, and these results were confirmed by the enzymatic assay (WST-1).