Clinical and molecular characteristics of Klebsiella variicola and Klebsiella pneumoniae: Implications for management and infection control.

OBJECTIVE

To systematically delineate clinical, resistance and virulence profiles of Klebsiella variicola (Kv) and Klebsiella pneumoniae (Kp) to inform species-specific management strategies.

METHODS

A retrospective 1:4 matched case-control study enrolled 32 Kv and 128 Kp isolates from Xuanwu Hospital (Jan 2022-Dec 2025). Identification of isolates utilised MALDI-TOF MS and rpoB sequencing. Clinical characteristics, antimicrobial susceptibility, biofilm-forming capacity, serum resistance and genetic determinants were analysed using standard statistical methods.

RESULTS

Among 2454 K. pneumoniae complex isolates, Kv accounted for 1.3%. Kv exhibited significantly lower resistance, particularly to carbapenems (3.1% vs. 35.2%; FDR-adjusted q < 0.001), lacking blaKPC entirely (0% vs. 30.5%). Both species were 100% susceptible to aztreonam-avibactam (AZA); however, one Kv harboured a transferable blaNDM. Kp showed higher carriage of classical virulence determinants (e.g., iutA+iucA, 28.1% vs. 0%) and greater serum resistance. Conversely, 90.6% of Kv lacked these genes, with 62.5% displaying high serum sensitivity. Although intra-abdominal Kv initially formed stronger biofilms (75.0% vs. 12.5%), multivariable regression revealed indwelling tubes (aOR: 6.84, P < 0.001), not species, independently drove robust biofilm formation. Clinical mortality did not differ significantly.

CONCLUSIONS

Kp tends to exhibit stronger virulence and resistance profiles, whereas Kv appears to act primarily as an opportunistic pathogen linked to device vulnerabilities. Accurate differentiation may facilitate tailored management (e.g., source control), with AZA emerging as a promising therapeutic option. However, these single-centre findings warrant extensive validation in larger multi-centre cohorts.