Colony types and virulence traits of Legionella feeleii determined by exopolysaccharide materials

Two genomic regions encoding exopolysaccharide production systems have complementary functions in B. cereus multicellularity and host interaction

Bacterial physiology and adaptation are influenced by the exopolysaccharides (EPS) they produce. These polymers are indispensable for the assembly of the biofilm extracellular matrix in multiple bacterial species. In a previous study, we described the profound gene expression changes leading to biofilm assembly in B. cereus ATCC14579 (CECT148). We found that a genomic region putatively dedicated to the synthesis of a capsular polysaccharide (eps2) was overexpressed in a biofilm cell population compared to in a planktonic population, while we detected no change in the transcript abundance from another genomic region (eps1) also likely to be involved in polysaccharide production. Preliminary biofilm assays suggested a mild role for the products of the eps2 region in biofilm formation and no function for the products of the eps1 region. The aim of this work was to better define the roles of these two regions in B. cereus multicellularity. We demonstrate that the eps2 region is indeed involved in bacterial adhesion to surfaces, cell-to-cell interaction, cellular aggregation and biofilm formation, while the eps1 region appears to be involved in a kind of social bacterial motility. Consistent with these results, we further demonstrate using bacterial-host cell interaction experiments that the eps2 region is more relevant to the adhesion to human epithelial cells and the zebrafish intestine, suggesting that this region encodes a bacterial factor that may potentiate gut colonization and enhance pathogenicity against humans.

Legionella feeleii: pneumonia or Pontiac fever? Bacterial virulence traits and host immune response

Gram-negative bacterium Legionella is able to proliferate intracellularly in mammalian host cells and amoeba, which became known in 1976 since they caused a large outbreak of pneumonia. It had been reported that different strains of Legionella pneumophila, Legionella micdadei, Legionella longbeachae, and Legionella feeleii caused human respiratory diseases, which were known as Pontiac fever or Legionnaires' disease. However, the differences of the virulence traits among the strains of the single species and the pathogenesis of the two diseases that were due to the bacterial virulence factors had not been well elucidated. L. feeleii is an important pathogenic organism in Legionellae, which attracted attention due to cause an outbreak of Pontiac fever in 1981 in Canada. In published researches, it has been found that L. feeleii serogroup 2 (ATCC 35849, LfLD) possess mono-polar flagellum, and L. feeleii serogroup 1 (ATCC 35072, WRLf) could secrete some exopolysaccharide (EPS) materials to the surrounding. Although the virulence of the L. feeleii strain was evidenced that could be promoted, the EPS might be dispensable for the bacteria that caused Pontiac fever. Based on the current knowledge, we focused on bacterial infection in human and murine host cells, intracellular growth, cytopathogenicity, stimulatory capacity of cytokines secretion, and pathogenic effects of the EPS of L. feeleii in this review.