previously . During the first 48 h of infection, H63T replicated by approximately two logs, indicating that H63T is quite adept at intracellular replication (Fig. S4a). In comparison, L.pneumophila ATCC BAA-74 displayed approximately 4 logs of growth during 48 h of infection (Fig. S4a). H63T was next examined for its ability to grow and survive within the lungs of 6- to 8-week-old A/J mice following intratracheal inoculation with 106 c.f.u. stationary-phase BCYE agar-grown bacteria . The numbers of H63T bacteria increased approximately 5-fold by 48 h post-inoculation, indicating that the strain can grow in the mammalian lung (Fig. S4b). This level of growth was comparable to what we and others have observed for L.pneumophila inoculated into A/J mice . After 48 h post-inoculation, the numbers of H63T bacteria decreased steadily (Fig. S4b), presumably due to bacterial clearance from the lung by the innate immune response. Compatible with the acute infection observed, histopathological examination of haematoxylin/eosin-stained lung sections taken from infected mice at 72 h post inoculation displayed irregular interstitial inflammation with moderate mononuclear infiltrate (not shown), indicative of pneumonia, as has been observed previously in A/J mice infected with L.pneumophila for 72 h . At 24 h post inoculation, 4.5 logs of H63T were present in the spleen, and the bacterial burden remained at that level for an additional 24 h (Fig. S4c). After 48 h, the numbers of bacteria in the spleen decreased and, by the fifth day, H63T was detectable in the spleen of only one of the five animals. In summary, H63T replicates significantly within both human macrophages and the murine lung, indicating that the strain is pathogenic, compatible with its isolation from a human patient experiencing severe illness.