OmpK35/36 modulate the virulence of hypervirulent Klebsiella pneumoniae by regulating capsular polysaccharide export.

OBJECTIVE

This study aimed to investigate the impact of outer membrane proteins 35 (OmpK35) and 36 on the virulence of Klebsiella pneumoniae and the corresponding mechanisms.

METHODS

Serotype K1 strain NTUH-K2044 was utilized to create single-deletion mutants (ΔompK35 and ΔompK36) and a double-deletion mutant (ΔompK35/36), alongside their complementation variants. Multiple analyses were performed, including capsule staining, transmission electron microscopy, serum resistance assays, phagocytosis tests, and infection models using mice and Galleria mellonella.

RESULTS

The mutants retained hypercapsules similar to NTUH-K2044, but looser capsule structures revealed by transmission electron microscopy. All mutants exhibited decreased virulence, with median lethal doses under 5 × 10⁴ colony forming units in mice. Specifically, only ΔompK35/36 showed reduced serum resistance compared to the wild strain, similar for the anti- phagocytosis capabilities. Additionally, ΔompK35 induced liver inflammation, whereas ΔompK36 and ΔompK35/36 exerted milder effects. Despite these differences, all mutants displayed normal growth rates and upregulated expression of gnd and wcaJ, crucial for capsular polysaccharide (CPS) biosynthesis.

CONCLUSIONS

The hypercapsule, composed mainly of CPS, plays a crucial role in the hypervirulence of K. pneumoniae. OmpK35/36 may modulate the virulence of K. pneumoniae by regulating CPS export.