Genotypes, antibiotic resistance, and virulence diversity among Klebsiella pneumoniae species complex isolates in Taiwan

Background Klebsiella pneumoniae , K. quasipneumoniae , and K. variicola are members of the K. pneumoniae species complex ( Kp SC) with distinct genotypes, virulence, and antibiotic resistance traits. However, their distribution and characteristics in Taiwan remain unknown. Methods We evaluated 809 Kp SC isolates (377 from bacteremia and 432 from urinary tract infections) collected at National Cheng Kung University Hospital (NCKUH) (1999–2022), identified by multiplex PCR and 16S rDNA sequencing, and characterized by antimicrobial susceptibility testing, virulence gene profiling, capsular typing, biofilm assays, and Galleria mellonella larvae infection models. Results Among the 809 Kp SC isolates, 752 (93.0%) were identified as Klebsiella pneumoniae , 37 (4.6%) as K. quasipneumoniae , and 20 (2.4%) as K. variicola . MALDI-TOF was unable to identify any of the 37 K. quasipneumoniae isolates correctly, but it accurately identified 17 of the 20 K. variicola isolates. K62 was the most prevalent capsular type among K. pneumoniae isolates (7/50, 14%), while K54 was the most common among K. quasipneumoniae isolates (5/37, 13.5%). Among the 20 K. variicola isolates, K35 and K49 were the major capsular serotypes, each represented by three isolates (3/20, 15%). Notably, 16.8% of Kp SC isolates could not be assigned to any serotype based on wzi sequencing. The prevalence of iucA , iroB , irp1 , irp2 , p rmpA , p rmpA2 , and peg-344 was significantly higher in K. pneumoniae than in K. quasipneumoniae and K. variicola . In contrast, only kfuBC was more common in K. variicola than in K. pneumoniae and K. quasipneumoniae . The virulence score was highest in K. pneumoniae (6.2 genes), followed by K. quasipneumoniae (4.6 genes) and K. variicola (4.4 genes) ( p = 0.002). K. pneumoniae demonstrated significantly higher resistance rates to gentamicin ( p = 0.005), ciprofloxacin ( p = 0.013), levofloxacin ( p = 0.003), and sulfamethoxazole/trimethoprim ( p = 0.036), compared to K. quasipneumoniae and K. variicola . The biofilm formation capacity of K. pneumoniae was found to be higher than that of K. quasipneumoniae and K. variicola . However, on day seven, the survival rate of larvae infected with K. pneumoniae was 25.1%, while only 9.7% and 8.5% of larvae survived in K. quasipneumoniae and K. variicola , respectively ( p < 0.0001). Conclusion K. pneumoniae , K. quasipneumoniae , and K. variicola in Taiwan exhibit distinct genotypic and phenotypic characteristics. K. quasipneumoniae and K. variicola displayed higher mortality in larvae infection model, underscoring the importance of continued surveillance of their dissemination.