This study established an experimental model of replicative
Legionella longbeachae
infection in
A/J mice. The animals were infected by intratracheal inoculation of 10
3
–10
9
c.f.u.
L. longbeachae
serogroup 1 (USA clinical isolates D4968, D4969 and D4973). The inocula of 10
9
,10
8
,10
7
and
10
6
c.f.u. of all tested
L. longbeachae
serogroup 1 isolates were lethal for A/J mice. Inoculation
of 10
5
c.f.u.
L. longbeachae
caused death in 90% of the animals within 5 days, whilst inoculation
of 10
4
c.f.u. caused sporadic death of mice. All animals that received 10
3
c.f.u. bacteria developed
acute lower respiratory disease, but were able to clear
Legionella
from the lungs within 3 weeks.
The kinetics of bacterial growth in the lungs was independent of inoculum size and reached a
growth peak about 3 logarithms above the initial inoculum at 72 h after inoculation. The most
prominent histological changes in the lungs were observed at 48–72 h after inoculation in the
form of a focal, neutrophil-dominant, peribronchiolar infiltration. The inflammatory process did not
progress towards the interstitial or alveolar spaces. Immunohistological analyses revealed
L.
longbeachae
serogroup 1 during the early phase of infection near the bronchiolar epithelia and
later co-localized with inflammatory cells. BALB/c and C57BL/6 mice strains were also
susceptible to infection with all
L. longbeachae
serogroup 1 strains tested and very similar
changes were observed in the lungs of infected animals. These results underline the infection
potential of
L. longbeachae
serogroup 1, which is associated with high morbidity and lethality in
mic