Deciphering the relative importance of genetic elements in hypervirulent Klebsiella pneumoniae to guide countermeasure development
Thomas A. Russo, Ulrike MacDonald, Zachary J. Drayer, Connor J. Davies, Cassandra L. Alvarado, Alan D. Hutson, Ting L. Luo, Melissa J. Martin, Patrick McGann, François Lebreton
Abstract
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 10 LD 50 (range 1.5–2.9)) were created to measure the effects on LD 50 in a murine model of the hypervirulence-associated plasmid (pVir), iucA , p rmpA , p rmpA2 (truncated) , irp2 , and clbBC . Findings Curing pVir had the greatest increase in survival (mean LD 50 to 7.6 (range 7.0–9.0, p ≤ 0.0001), a dosage comparable to classical K. pneumoniae . Results also showed increased mean LD 50 s for Δ p rmpA (5.9, p ≤ 0.0001), Δ iucA (3.6, p ≤ 0.0001), Δ irp2 (3.4), Δ rmpA Δ iucA (6.3, p ≤ 0.0001), and ΔpVirΔ irp2 (8.7, p ≤ 0.0001). Notably ΔpVir had an additional mean LD 50 increase of 1.3 compared to the pVir-encoded Δ p rmpA Δ iucA (p ≤ 0.01), suggesting presence of additional pVir-virulence genes. Truncated p RmpA2 did not contribute to virulence. Odd ratios in the absence of pVir/yersiniabactin, pVir, p RmpA/aerobactin, p 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.