Molecular characterisation of carbapenem- and tigecycline-resistant Klebsiella pneumoniae strains isolated from blood and bile samples

Introduction: The number of carbapenem-resistant Klebsiella pneumoniae (CRKP) strains are increasing, further raising healthcare concerns worldwide. In this study, we isolated three CRKP strains from bile and blood samples of an elderly patient (90s) with acute cholangitis and characterised the features and antimicrobial resistance mechanism of CRKP isolates. Methods: Three CRKP isolates were characterised by Pulsed-field gel electrophoresis (PFGE), whole genome sequencing using the NovaSeq 6000, and antimicrobial susceptibility testing. Transcriptional levels of resistance-associated genes were measured by real-time RT-qPCR. Results: PFGE analysis revealed highly similar patterns for these isolates. Furthermore, they showed resistance to not only carbapenem but also tigecycline. Genomic analysis of the blood isolate identified the exogenous resistance genes bla(CTX-M14), tet(A), tet(D), opxAB, and qnrS1 but not any carbapenemase-encoding genes. In addition, nonsense mutations were found in both the outer membrane protein K36 (ompK36) and transcriptional regulator ramR, suggesting that this isolate developed multidrug resistance by acquiring both exogenous resistance genes and nonsense mutations. The extended-spectrum beta-lactamase-producing carbapenem-susceptible K. pneumoniae isolate exhibited the same susceptibility pattern, except to beta-lactams, as prior CRKP isolates. Conclusions: Antimicrobial susceptibility to carbapenem and tigecycline should be continuously monitored, because it might change from susceptible to resistant during another antimicrobial treatment, even if an isolate initially shows susceptibility, and the patient has not been exposed to these agents.