Grouping of 20 reference strains of Legionella species by the growth ability within mouse and guinea pig macrophages

Abstract

20 Reference strains of Legionella species, isolated from human, were classified according to their ability to grow within thioglycolate-induced peritoneal macrophages of mice and guinea pigs. Inbred and congenic mice were used to study the effect of the natural resistance genes Lgn1 and Bcg that are expressed phenotypically in the mouse macrophages. The Lgn1 gene controlled the intracellular growth of Legionella pneumophila Philadelphia-1 and Legionella jordanis GIFU 12657, but the Bcg gene did not affect the intracellular growth of any organism examined. Based on these results and the growth ability in guinea pig macrophages, the 20 reference strains were divided into four groups. This grouping will help us to understand a variety of modes of interaction between Legionella species and macrophages.

Comparative assessment of virulence traits in Legionella spp.

“…There is no direct correlation with the grouping in this study, which could be due to the differences in the strains and/or methods of classification. This is not surprising as Izu et al (1999) found no significant characteristics common to another grouping done by Neumeister et al (1997), which was based on the bacterial doubling time in Mono Mac 6 cells and Acanthamoeba castellanii. Our data on L. cincinnatiensis are consistent with the finding of Izu et al (1999) that this species of Legionella does not grow within U937 cells despite the fact there might be some strain differences and different host cell lines used.…”

“…This is not surprising as Izu et al (1999) found no significant characteristics common to another grouping done by Neumeister et al (1997), which was based on the bacterial doubling time in Mono Mac 6 cells and Acanthamoeba castellanii. Our data on L. cincinnatiensis are consistent with the finding of Izu et al (1999) that this species of Legionella does not grow within U937 cells despite the fact there might be some strain differences and different host cell lines used. However, the main objective of this study was not to provide a classification method for Legionella spp., but rather to provide a better understanding of the pathogenic trait(s) that could be responsible for variation in the virulence of these bacteria.…”

“…has been carried out previously using mouse and guinea pig macrophages. Izu et al (1999) grouped 20 reference strains into four groups. In contrast, our classification based on cytopathogenicity divided 27 strains of Legionella spp.…”

“…into two broad main groups. Group I classification by Izu et al (1999) includes most of the group II strains in our study along with L. dumoffii. There is no direct correlation with the grouping in this study, which could be due to the differences in the strains and/or methods of classification.…”

“…apart from L. pneumophila are not well defined. Previous studies have addressed the replication of legionellae within human macrophage cell lines (O'Connell et al, 1996) and guinea pigs (Doyle et al, 2001;Izu et al, 1999). The growth of Legionella spp.…”