Table 1. Virulence of Y. pestis strains in a mouse model of septicemic plague.
| Strain or genotypea | LD50 valuesb | Virulence loss |
| Δpgm | <6 ± 2.8 (<8; 4) | -- |
| Δpgm Δznu | 5.7 × 106 ± 4.2 × 106 | >9.5 × 105-fold |
| Δpgm ΔznuBC attTn7∷znuABC+ | <10; >101; 25 | -- |
| Wild type | <14 ± 1.4 (<13; <15) | -- |
| Δznu | ∼11 ± 5 (<10; >16; <8; <18) | none |
| irp2∷kan | ∼ 48 (<11; 84.5) | none |
| irp2 Δznu | ∼6.0 × 106 ± 3.5 × 106 (5.1 × 106; 2.7 × 106; 5.4 × 106; >1.1 × 107) | >4.3 × 105-fold |
| Δpsn∷kan | <14 | none |
| Δpsn∷kan ΔznuBC | ∼40 ± 14 (30; <50) | none |
Strains: Δpgm – KIM5(pCD1Ap); Δpgm Δznu – KIM5-2077(pCD1Ap) [Δpgm ΔznuBC] and KIM5-2197(pCD1Ap) [Δpgm ΔznuA]; Δpgm ΔznuBC attTn7∷znuABC – KIM5-2077.10(pCD1Ap); wild type - KIM5(pCD1Ap)+; Δznu – KIM5-2077(pCD1Ap)+ [ΔznuBC] and KIM5-2197(pCD1Ap)+ [ΔznuA]; irp2∷kan – KIM5-2046.1(pCD1Ap); irp2 Δznu – KIM5-2077.7(pCD1Ap) [irp2∷kan ΔznuBC], KIM5-2077.8(pCD1Ap) [Δirp2 ΔznuBC] and KIM5-2197.1(pCD1Ap) [Δirp2 ΔznuA]; Δpsn∷kan – KIM5-2045.6(pCD1Ap); Δpsn∷kan ΔznuBC – KIM5-2077.9(pCD1Ap). In all backgrounds tested, an in-frame ΔznuA mutation and the ΔznuBC mutation caused similar LD50s. In addition, irp2∷kan and Δirp2 mutations in all backgrounds tested yielded similar LD50s. These LD50s were combined and genotypes for these strains are listed in the table as Δznu, Δpgm Δznu, and irp2 Δznu.
Where the LD50 was lower than the lowest dose of the trial (e.g., <8) or higher than the highest dose (e.g., >16), these doses and the calculated LD50s are given in parentheses (e.g., <8; 4) and were used in calculating the mean LD50. The means ± standard deviations from two to four separate trials are given, except for the Δpgm ΔznuBC attTn7∷znuABC+ strain were the LD50s of three separate trials are listed.