Jd. Cirillo et al., Intracellular growth in Acanthamoeba castellanii affects monocyte entry mechanisms and enhances virulence of Legionella pneumophila, INFEC IMMUN, 67(9), 1999, pp. 4427-4434
Since Legionella pneumophila is an intracellular pathogen, entry into and r
eplication within host cells are thought to be critical to its ability to c
ause disease. L, pneumophila grown in one of its environmental hosts, Acant
hamoeba castellanii, is phenotypically different from L. pneumophila grown
on standard laboratory medium (BCYE agar). Although amoeba-grown L. pneumop
hila displays enhanced entry into monocytes compared to BCYE-grown bacteria
, the mechanisms of entry used and the effects on virulence have not been e
xamined. To explore whether amoeba-grown L. pneumophila differs from BCYE-g
rown L. pneumophila in these characteristics, we examined entry into monocy
tes, replication in activated macrophages, and virulence in mice. Entry of
amoeba-grown L. pneumophila into monocytes occurred more frequently by coil
ing phagocytosis, was less affected by complement opsonization, and was Les
s sensitive to microtubule and microfilament inhibitors than was entry of B
CYE-grown bacteria. In addition, amoeba-grown L. pneumophila displays incre
ased replication in monocytes and is more virulent in A/J, C57BL/6 Beige, a
nd C57BL/6 mice. These data demonstrate for the first time that the intra-a
moebal growth environment affects the entry mechanisms and virulence of L.
pneumophila.