Deciphering the relative importance of genetic elements in hypervirulent Klebsiella pneumoniae to guide countermeasure development.

BACKGROUND

Quantitating the contribution of phenotype-responsible elements in hypervirulent Klebsiella pneumoniae is needed.

METHODS

Isogenic mutants of four hypervirulent clinical isolates that produced K1 (ST23), K2 (ST86), K20 (ST1544), or K54 (ST29) capsules (mean 2.2 log LD (range 1.5-2.9)) were created to measure the effects on LD in a murine model of the hypervirulence-associated plasmid (pVir), iucA, rmpA, rmpA2 (truncated), irp2, and clbBC.

FINDINGS

Curing pVir had the greatest increase in survival (mean LD to 7.6 (range 7.0-9.0, p ≤ 0.0001), a dosage comparable to classical K. pneumoniae. Results also showed increased mean LDs for ΔrmpA (5.9, p ≤ 0.0001), ΔiucA (3.6, p ≤ 0.0001), Δirp2 (3.4), ΔrmpAΔiucA (6.3, p ≤ 0.0001), and ΔpVirΔirp2 (8.7, p ≤ 0.0001). Notably ΔpVir had an additional mean LD increase of 1.3 compared to the pVir-encoded ΔrmpAΔiucA (p ≤ 0.01), suggesting presence of additional pVir-virulence genes. Truncated RmpA2 did not contribute to virulence. Odd ratios in the absence of pVir/yersiniabactin, pVir, RmpA/aerobactin, RmpA, aerobactin, yersiniabactin, and colibactin demonstrated a 250-fold, 67-fold, 20-fold, 16.7-fold, 9.6-fold, and 1.7-fold decrease in lethality respectively.

INTERPRETATION

These data can guide countermeasure development.

FUNDING

This work was supported by NIH R21 AI123558-01 and 1R21AI141826-01A1 (Dr. Russo) and the Department of Veterans Affairs VA Merit Review (I01 BX004677-01) (Dr. Russo). This study was also partially funded by the U.S. Defense Health Program (DHP) Operations and Maintenance.