engleski

The Pathogenic Potential of Legionella longbeachae in Genetically Different Mice

Background: Although, considered as an uncommon pathogen of Legionnaires´disease, Legionella longbeachae is responsible for up to half of the legionellosis in Australia. Transmission of Legionella from the environment to humans usually occurs via inhalation of Legionella-containing aerosols, but L. longbeachae has been detected only occasionally in water. It has been more commonly isolated from soil and decomposing materials. In this study we examined the pathogenic potential of Legionella longbeachae in genetically different mice, since previous studies indicate on the genetically driven permisivity of mice for L. pneumophila. Methods: A/J, BALB/c, and C57Bl/6 mice were infected by intratracheal inoculation of L. longbeachae (strain D4968) using doses from 102 to 105 CFU. In the infected animals we followed the mortality, clearance of bacteria, and histopathological changes in the lungs. Results: Irrespective of mouse strains the 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 for more than three weeks. Intensity of bacterial multiplication in the lungs was about three logarithm and reached a peak at 72 hours after inoculation (106-108 CFU/lung), decreasing thereafter to the detection level on day seven. Histological changes were observed 2-4 hours after inoculation in the form of an acellular bronchiolitis, followed at 24-48 hours post infection by an extravasation and alveolar infiltration with predominantly granulocytes. This is in constraint with changes seen in bronchoalveolar pneumonia. No pathological propagation was seen behind the bronchial basal membranes or towards the interstitial spaces. Conclusion: All three mice strains (A/J, BALB/c and C57Bl/6) are susceptible to infection with L. longbeachae. The LD90 and particulary the LD50 dose was very low indicating a high infectivity potential of L. longbeachae. Early histopathological changes of lung structures may be caused with some in vivo induced virulence factor(s).

Legionella longbeachae; lung infection; mouse model

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