engleski

Experimental Legionella longbeachae lung infection in intratracheally inoculated mice

Legionella longbeachae was described as a new species of Legionellaceae in 1981, when it was isolated from a patient with pneumonia. Since then many infections due to L. longbeachae have been reported in Norht America, Europe and Australia. Most of the studies undertaken to understand the pathogenesis of Legionella infections have focused on L. pneumophila and L. micdadei. Wishing to contribute to the understanding of the pathogenic mechanisms, we established an experimental model of replicative L. longbeachae (D4968 strain) infection in A/J mice. The animals were infected by intratracheal inoculation using various doses of L. longbeachae (from 10000 to 1000000000). In comparison to the results of our earlier studies using Legionella pneumophila we showed that the letal dose of L. longbeachae was more than 100-fold lower than that of L. pneumophila. Furthermore, the histological appearance of the lungs taken from infected mice was consistent with severe acute pneumonia, characterised by engorgment of the alveolar spaces with fluid and a large number of neutrophils and monocytes. Besides analysing lung pathohistology and bacterial counts in the lungs we also followed the dissemination of L. longbeachae into other organs. The bacteria could be also isolated from the blood, liver, spleen, kidney and brain tissues, already 24-hours after intratracheal inoculation. The obtained results underline the importance of this species as a causative agent of acute lung infection and further studies should elucidate the factors included in the pathogenic process.

Legionella longbeachae; pneumonia; murine model

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