TABLE 3.
Virulence of A. pleuropneumoniae parent and isogenic mutant strains following aerosol challenge
| Trial no. and A. pleuro pneumoniae challenge strain | Challenge dose (CFU [aerosolized] per 4 pigs) | Time of analysis (day)a | Serological response with:
|
No. of animals with lung lesions/ total no. | Arithmetic mean ± SD of lung lesion scoreb,c | No. of animals with reisolation of A. pleuropneumoniae at post- mortem analysis/total no.
|
|||||
|---|---|---|---|---|---|---|---|---|---|---|---|
| Detergent washd | ApxIIAc | Tonsil | Lymph node | Heart | Lung
|
||||||
| Pneumonic | Intact | ||||||||||
| Trial 1 | |||||||||||
| AP76 wt | 3.6 × 104 | 21 | 7,800 ± 4,480 | 18.4 ± 15.5 | 7/8 | 10.09 ± 10.03 | 6/8 | 3/8 | 4/8 | 5/6 | 4/8 |
| AP76 ΔaspA | 6.7 × 104 | 21 | 10,300 ± 11,217f | 27.9 ± 23.5e | 4/8f | 4.90 ± 4.96 | 6/8 | 2/8 | 3/8 | 4/5 | 3/8 |
| Trial 2 | |||||||||||
| AP76 wt | 6.76 × 104 | 7 | 2,808 ± 2,794 | 2.5 ± 2.2 | 7/8 | 11.38 ± 7.84 | 7/8 | 8/8 | 7/8 | 7/7 | 8/8 |
| AP76 ΔaspA | 16.38 × 104 | 7 | 2,400 ± 855 | 1.9 ± 0.6 | 8/8 | 6.89 ± 2.59 | 7/8 | 7/8 | 5/8 | 8/8 | 8/8 |
| AP76 ΔaspAΔdmsA | 11.05 × 104 | 7 | 3,400 ± 2,627 | 2.1 ± 0.8 | 4/4 | 6.07 ± 2.05 | 1/4 | 3/4 | 2/4 | 4/4 | 1/4 |
| AP76 wt | 6.76 × 104 | 21 | 38,400 ± 14,780 | 55.8 ± 12.8 | 4/4 | 15.02 ± 11.26 | 2/4 | 4/4 | 1/4 | 4/4 | 4/4 |
| AP76 ΔaspAΔdmsA | 11.05 × 104 | 21 | 58,933 ± 57,735 | 43.3 ± 30.2 | 3/3 | 5.70 ± 3.00 | 3/3 | 1/3 | 1/3 | 3/3 | 1/3 |
Day after infection on which animals were sacrificed, postmortem analysis was performed, and antibody titers were determined.
The lung lesion score was determined as described previously by Hannan et al. (21).
Although the lung lesion scores of animals infected with AP76 ΔaspA and AP76 ΔaspA ΔdmsA are lower than those observed for animals infected with the AP76 wild type, this difference is not statistically significant (P = 0.11 for AP76 ΔaspA and P = 0.24 for AP76 ΔaspAΔdmsA; Wilcoxon test).
The solid-phase antigen was prepared as described previously (17); the number given is the arithmetic mean of the highest serum dilution resulting in an optical density twice as high as that of the negative control serum at a dilution of 1:100.
Recombinant ApxII was used as a solid-phase antigen as described previously (28); the number given is the arithmetic mean of the serum activity in enzyme-linked immunosorbent assay units.
One animal was euthanized on day 6 after infection due to rectal prolapse. This animal was included in the lung lesion score and reisolation analysis but excluded from determination of serological response.