engleski

The susceptibility of different mouse strains to Legionella longbeachae infection

Objectives:Since the first isolation of Legionella longbeachae in 1981 it was considered as an uncommon pathogen of Legionnaires´disease. Today we are aware that, besides some individual cases observed in Japan, USA, Spain, Germany and France, L. longbeachae is responsible for up to half of the legionellosis in Australia. In contrast to L. pneumophila, this bacteria has been detected only occasionally in water. More commonly, it has been isolated from soil and decomposing materials. In this study we examined the pathogenesis of Legionella longbeachae (strain D4968) lung infection in different mice strains, since previous studies pointed to a genetically driven permisivity of mice to L. pneumophila (BALB/c and C57Bl/6 mice are highly resistant and A/J mice susceptible). Methods: A/J, BALB/c, and C57Bl/6 mice were infected by intratracheal inoculation of L. longbeachae using different doses from 102 to 105 CFU. In the infected animals we followed the bacterial clearance from lung tissue, mortality assay and histopathological changes in the lungs. Results: Irrespective of mouse strains the intratracheal inoculation of 105 L. longbeachae caused death in 90% of the animals within six days.The LD50 dose of L. longbeachae for all mice strains was determined at 104 CFU. The animals that received 102 or 103 bacteria survived 14 days post inoculation. During that period the multiplication of bacteria in the lungs reached a peak at 72 hours after inoculation (106-108 CFU/lung) and thereafter decreased gradually to the detection level on day seven.Histological appearance of the lungs taken from infected animals was constraint with bronchoalveolar pneumonia. Conclusion: Our results indicate that all three mice strains are susceptible to infection with L. longbeachae. The LD90 and particulary LD50 dose was unusaully low indicating a high infectivity potential of L. longbeachae. Histopathological changes in the lung tissue, indicate on a bronchopneumonia rather than on interstitial pneumonia as seen in L. pneumophila infection.

Legionella longbeachae; legionellosis; murine model

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