Importance:Hypervirulent variants of Klebsiella pneumoniae(hvKp)are capable of causing life-threatening pyogenic liver abscesses(PLAs),but hvKp caused PLAs was seldom reported in pediatric populations.Hence,there is an urgent need to raise our awareness of this phenomenon in pediatric populations.Objective:This study aimed to report the clinical characteristics of hvKp that caused fatal PLA complicated by bacteremia in an adolescent and further identify the microbiological and genomic features of the causative strain.Methods:A 14-year-old boy with diabetes mellitus was admitted to our hospital with a diagnosis of PLA complicated by bacteremia.A hypermucoviscous hvKp strain,KPN_19-106,was isolated from the drainage fluid present within the liver abscess cavity and blood.The hypermucoviscosity phenotype of the causative strain was determined by string test.Its virulence was measured using serum resistance assay and Galleria mellonella larvae-killing assay.Antimicrobial susceptibility was determined by broth microdilution method.Genetic information was obtained by whole-genome sequencing and bioinformatics analysis.Results:KPN_19-106 belonged to sequence type 380 and serotype K2 and exhibited stronger serum resistance and higher in vivo lethality than the well-characterized hvKp NTUH-K2044 strain.Although KPN19-106 is susceptible to most antibiotics,no sign of improvement was observed during treatment with such drugs.Whole-genome sequencing revealed that the isolate had integrated multiple mobile genetic elements related to virulence.Interpretation:Antibiotic-susceptible hvKp can cause fatal PLA complicated by bacteremia in adolescents,with no improvement during antimicrobial therapy.The causative strain in this case had integrated multiple virulence genes and thus exhibited higher virulence both in vitro and in vivo when compared with NTUH-K2044.