Do natural plasmids play a role in mediating virulence in multidrug-resistant bacterium Klebsiella pneumoniae?

Background and aims: Antibiotic resistance is a serious public health threat. A major source for antibiotic resistance and spread are natural MDR transferrable plasmids. Klebsiella pneumoniae (Kpn) is one of the dangerous MDR pathogens responsible for various human infections and MDR is often due to carriage of plasmids that encode extended-spectrum-β-lactamases (ESBL). We showed that ESBL-producing (ESBL-P) Kpn are more virulent than non-ESBL strains. We aimed to explore the contribution of ESBL-plasmids on bacterial virulence.

Methods: We studied two ESBL-P MDR Kpn isolates- KpnB199 (bloodstream infection) and KpnU95 (urinary tract infection). Strains were genotyped (MLST), and their ESBL genes were identified (PCR). Virulence assessment included capsule production, biofilm formation, and survival in human sera. Escherichia coli DH10B transformants carrying the Kpn ESBL-plasmids were studied for assessing plasmid effects on virulence.

Results: KpnB199 and KpnU95 belonged to sequence types ST327 and ST1412, respectively. Kpn199 carried an ESBL-plasmid encoding CTX-M-2, and KpnU95 produced CTX-M-15. KpnB199 was significantly more virulent compared to KpnU95 in all parameters tested (p<0.05). It produced more capsule (1.8-fold), produced more (2-fold) biofilm, and proliferated in human serum demonstrating its serum resistance. In contrast, KpnU95 died in human sera (12% survival). E.coli DH10B showed poor virulence compared to Kpn strains. The virulence of the two E.coli transformants carrying pKpnB199 or pKpnU95 ESBL-plasmids was not effected by plasmid acquisition.

Conclusions: We observed differences in the virulence of Kpn isolates; however, we could not conclusively find evidence that the ESBL plasmids contribute to E. coli virulence and further studies are required.