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Query: UMLS:C0023241 (Legionella)
 6,990 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

A model of intracellular growth for Legionella pneumophila in Acanthamoeba castellanii has been developed and provides a quantitative measure of survival and replication after entry. In this model, Acanthamoeba monolayers were incubated with bacteria in tissue culture plates under nutrient-limiting conditions. Gentamicin was used to kill extracellular bacteria following the period of incubation, and the number of intracellular bacteria was determined following lysis of amebae. Intracellular growth of virulent L. pneumophila and other wild-type Legionella species was observed when the assay was performed at 37 degrees C. At room temperature, none of the Legionella strains tested grew intracellularly, while an avirulent L. pneumophila strain was unable to replicate in this assay at either temperature. The effect of nutrient limitation on A. castellanii during the assay prevented multiplication of the amebae and increased the level of infection by Legionella spp. The level of infection of the amebae was directly proportional to the multiplicity of infection with bacteria; at an inoculum of 1.03 x 10(7) bacteria added to wells containing 1.10 x 10(5) amebae (multiplicity of infection of 100), approximately 4.4% of A. castellanii cells became infected. Cytochalasin D reduced the uptake of bacteria by the amebae primarily by causing amebae to lift off the culture dish, reducing the number of target hosts; methylamine also reduced the level of initial infection, yet neither inhibitor was able to prevent intracellular replication of Legionella spp. Consequently, once the bacteria entered the cell, only lowered temperature could restrict replication. This model of intracellular growth provides a one-step growth curve and should be useful to study the molecular basis of the host-parasite interaction.
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PMID:A quantitative model of intracellular growth of Legionella pneumophila in Acanthamoeba castellanii. 172 91

Legionella pneumophila is a gram-negative facultative intracellular parasite that causes Legionnaires disease. To explore the interactions between L. pneumophila and host cells, we have developed a continuous cell line model of infection. We show that about 80% of Chinese hamster ovary (CHO) cells were associated with L. pneumophila after incubation for 3 h at a multiplicity of infection of 20 bacteria per cell. Within 3 to 4 h of incubation with L. pneumophila, protein synthesis of CHO cells was markedly inhibited, as shown by the reduction of incorporation of radiolabeled amino acids into proteins. L. pneumophila did not inhibit transport of amino acids or cause degradation of newly synthesized proteins in CHO cells. Cytochalasin D blocked internalization of L. pneumophila by CHO cells, yet CHO cell protein synthesis was inhibited. These results indicated that L. pneumophila could inhibit host protein synthesis from the cell exterior. L. pneumophila that had been killed with antibiotics prior to incubation with CHO cells still inhibited protein synthesis, indicating that the inhibition of CHO cell protein synthesis occurred in the absence of de novo protein synthesis by L. pneumophila.
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PMID:Legionella pneumophila inhibits protein synthesis in Chinese hamster ovary cells. 198 39

A cloned and axenically cultured strain of Hartmannella vermiformis was used as a model to study intracellular multiplication of Legionella pneumophila in amoebae. The growth of L. pneumophilia in both H. vermiformis and a human monocyte-like cell line (U937) was investigated with cytoskeletal and metabolic inhibitors. L. pneumophila replicated only intracellularly in these cellular models, and electron microscopy showed ultrastructural similarities in the initial phase of multiplication. Treatment of amoebae with an inhibitor of microfilament-dependent phagocytosis (cytochalasin D, 0.5 or 1.0 micrograms/ml) did not inhibit intracellular growth of L. pneumophila; however, intracellular multiplication was inhibited by treatment of U937 monocytes with the same concentrations of cytochalasin D. Methylamine (10 to 100 mM), an inhibitor of adsorptive pinocytosis, inhibited the replication of L. pneumophila in amoebae in a dose-dependent manner. All doses of methylamine tested (10 to 50 mM) inhibited growth of L. pneumophila in U937 monocytes. Cytochalasin D and methylamine had no effect on the multiplication of L. pneumophila in culture medium or on the viability of amoebae or U937 monocytes. Intracellular replication of L. pneumophila in H. vermiformis may be accomplished by a cytochalasin D-independent mechanism, such as adsorptive pinocytosis. In contrast, both cytochalasin D- and methylamine-sensitive mechanisms may be essential for the intracellular multiplication of L. pneumophila in U937 monocytes.
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PMID:Effects of cytochalasin D and methylamine on intracellular growth of Legionella pneumophila in amoebae and human monocyte-like cells. 199 28