MULTIPLICATION OF DIFFERENT LEGIONELLA SPECIES IN MONO MAC-6 CELLS AND IN ACANTHAMOEBA-CASTELLANII

Survival and distribution of legionellae in the environment are assume d to be associated with their multiplication in amoebae, whereas the a bility to multiply in macrophages is usually regarded to correspond to pathogenicity, Since most investigations focused on Legionella pneumo phila serogroup 1, we examined the intracellular multiplication of dif ferent Legionella species in Mono Mac 6 cells, which express phenotypi c and functional features of mature monocytes, and in Acanthamoeba cas tellanii, an environmental host of Legionella spp, According to the ba cterial doubling time in Mono Mac 6 cells and in A. castellanii, seven clusters of legionellae could be defined which could be split further with regard to finer differences, L. longbeachae serogroup 1, L. jord anis, and L. anisa were not able to multiply in either A. castellanii or Mono Mac 6 cells and are members of the first cluster, L. dumoffi d id not multiply in Mono Mac 6 cells but showed a delayed multiplicatio n in A. castellanii 72 h after infection and is the only member of the second cluster, L. steigerwaltii, L. gormanii, L. pneumophila serogro up 6 ATCC 33215, L. bozemanii, and L. micdadei showed a stable bacteri al count in Mono Mac 6 cells after infection but a decreasing count in amoebae, They can be regarded as members of the third cluster, As the only member of the fourth cluster, L. oakridgensis was able to multip ly slightly in Mono Mac 6 cells but was killed within amoebae, A strai n of L. pneumophila serogroup 1 Philadelphia obtained after 30 passage s on SMH agar and a strain of L. pneumophila serogroup 1 Philadelphia obtained after intraperitoneal growth in guinea pigs are members of th e fifth cluster, which showed multiplication in Mono Mac 6 cells but a decrease of bacterial counts in A. castellanii. The sixth cluster is characterized by intracellular multiplication in both host cell system s and consists of several strains of L. pneumophila serogroup 1 Philad elphia, a strain of L. pneumophila serogroup 2, and a fresh clinical i solate of L. pneumophila serogroup 6, Members of the seventh cluster a re a strain of agar-adapted L. pneumophila serogroup 1 Bellingham and a strain of L. pneumophila serogroup 1 Bellingham which was passaged f ewer than three times on BCYE alpha agar after inoculation and intrape ritoneal growth in guinea pigs. In comparison to members of the sixth cluster, both strains showed a slightly enhanced multiplication in Mon o Mac 6 cells but a reduced multiplication in amoebae, From our invest igations, we could demonstrate a correlation between prevalence of a g iven Legionella species and their intracellular multiplication in Mono Mac 6 cells, Multiplication of members of the genus Legionella in A. castellanii seems to be dependent on mechanisms different from those i n monocytes.