engleski

Comparison of the virulence of different Legionella longbeachae strains in A/J mice

Legionella longbeachae is the most common cause of legionellosis in many parts of Australia, while in Europe and the United States, it rarely causes disease. Epidemiological studies have shown that gardening is a major risk factor in acquaring L. longbeachae infection. In previous studies the virulence of L .longbeachae strains were studied on guinea pigs animal model, and a remarkable variations in signs and disease outcome was shown. Wishing to overcome the inconsistence of the previous animal model we established a murine model of experimental legionellosis caused by L. longbeachae. We have shown that mice intratracheally inoculated with10^5 CFU L. longbeachae serogroup 1 (strain D4968) developed an acute disease and died within six days. In this study we were interested to explore if there was differences in virulence between L. longbeachae serogroup 1strains. The isolates of L.longbeachae serogroup 1 investigated in this study included: 2 clinical (A5H5 and A4C5) and 2 environmental (L6C9 and K8B9) Australian isolates as well as 3 clinical isolates from the United States (D4968, D4969, D4973). Inbread A/J mice 6 to 8 weeks old were intratracheally inoculated with dose 10^5 CFU of bacteria. We followed mortality rate, intensity of bacterial multiplication and patohistological changes in the lungs of infected mice 2, 24 48 and 72 hours post infection. Our previous studies have shown that10^5 CFU of L. longbeachae serogrup 1 (strain D4968) was LD90. All tested strains of L. longbeachae serogroup 1 caused death of A/J mice within 7 days. Then we followed the replication of different L. longbeachae serogroup 1 strains in the lungs of infected A/J mice. There were no significant differences between all tested strains. During 72 hours post infection, bacteria rapidly replicated in the lungs of infected A/J mice, reaching the concentration of 10^7 and 10^8 CFU. All tested strains caused the same patohistological changes in the lungs of A/J mice. These changes were in the form of multifocal bronchopneumonia. There were no significant differences in virulence of tested L. longbeachae serogroup 1 strains. Mice model seems to be a better experimental model to study the virulence of L. longbeachae infection.

Legionella spp.; legionellosis; mice model

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