Comparative profiling of virulence determinants, capsular serotypes, and antimicrobial resistance in hypervirulent and classical Klebsiella pneumoniae isolates from liver abscess patients

This study aimed to compare the virulence and resistance gene profiles, capsular serotypes, and molecular epidemiology of hypervirulent Klebsiella pneumoniae (hvKP) and classical Klebsiella pneumoniae (cKP) strains isolated from patients with liver abscesses in China, and to evaluate their phenotypic virulence using in vitro and in vivo models. A total of 83 non-repetitive K. pneumoniae strains were collected from liver abscess patients between January 2023 and December 2024. Strains positive for the string test and harboring both rmpA and iutA genes were classified as hvKP (n = 47), while the others were designated as cKP (n = 36). PCR was used to detect virulence genes (rmpA, iutA, aerobactin, magA, wcaG, kfu, fimH, mrkD, allS, iroB, ybtS, entB, peg-344, uge), capsular serotypes (K1, K2, K5, K20, K54, K57), and resistance genes (KPC, NDM, TEM, CTX-M-1). Multilocus sequence typing (MLST) was performed to determine sequence types. Virulence was further assessed through serum resistance assays, biofilm formation tests, and a Galleria mellonella infection model. The hvKP group showed significantly higher carriage rates of nine virulence genes (rmpA, iutA, aerobactin, magA, wcaG, kfu, allS, peg-344, iroB) compared to cKP (all P < 0.05), while fimH and mrkD were universally present. K1 was the predominant serotype in hvKP (63.8%), and magA and allS were exclusively detected in K1 strains. Serotypes K1 and K20 were significantly more frequent in hvKP than in cKP. MLST revealed that hvKP isolates belonged to eight STs, mainly ST23 and ST65, with all K1 strains corresponding to ST23. In contrast, cKP displayed greater ST diversity (17 STs). Resistance genes KPC, NDM, and CTX-M-1 were less prevalent in hvKP, and KPC was detected exclusively in cKP (16.7% vs. 0%, P < 0.05). Serum resistance was significantly stronger in hvKP than in cKP (P < 0.05), whereas biofilm formation did not differ significantly between groups. In the G. mellonella model, hvKP caused significantly higher mortality at inocula of 105, 106, and 107 CFU/mL (P < 0.05). HvKP isolates from liver abscesses in this region are characterized by a distinct molecular profile, including a high prevalence of K1/ST23 clones and key virulence genes. Although hvKP remains largely susceptible to carbapenems, the detection of CTX-M-1 in one hvKP strain signals potential convergence of virulence and resistance. These findings support the use of combined molecular and phenotypic assays for the timely identification of hvKP and underscore the need for ongoing surveillance to monitor the evolution of high-risk clones.