Comparison of Virulence of L. longbeachae to other Legionella Strains in an Animal Model

Legionella species are one of the causing agents of bacterial pneumonia. Legionella pneumophila accounts for the vast majority of cases in most of the world, with L. micdadei ranking distantly second. Most of the studies has been focused on the understanding the pathogenesis of pneumonia caused by L. pneumophila. Little is knows about the virulence of L. longebeachae although it’s leading cause of legionellosis in Australia. The aim of study was to determine the virulence of L. longbeachae in comparison to different Legionella strains including L. pneumophila, L. micdadei and L. steigerwaltii. An animal model of intratracheal infection was established on A/J mice. Our results showed that all the mice that received the dose of 105 CFU of L. pneumophila, L. micdadei, L. longbeachae serogroup 2 or L. steigerwaltii survived and cleared the infection while the mice infected with the same dose of L. longbeachae serogroup 1 developed severe bronchopneumonia and died within five days. Taken together, among all tested strains the most virulent one for mice was L. longbeachae serogroup 1.