[Structural dynamics of Legionella pneumophila and Legionella bozemanii colony/biofilm]

The genus Legionella includes very pleomorphic species responsible for disease outbreaks in humans. The appearance of such has great importance to develop artificial biofilms in aquatic ecosystems. The aim of this work was to study the dynamics of growth and evolution of the internal structure of colonies of representative species of the genus as static biofilm model.

Isolated colonies of Legionella pneumophila and Legionella bozemanii grown in specific media for three and fifteen days were processed for histological methods and embedded in paraffin and epoxy resin for analysis by light microscopy, electron microscopy and image analysis. RESULTS. In colonies of both species were observed and defined specific architectural patterns, based on stratification and evolve over time. The strata differ in the amount of extracellular matrix, the morphology and population density and the proportion of dead cells. The internal structure of three days colonies showed large differences between L. pneumophila (two layers) and L. bozemanii (four layers). However, in the fifteen days colonies of both species evolved towards a common unique pattern formed by three layers. In both species the growth was also found within the culture medium, although this phenomenon was more intense in L. bozemanii with unique, central and larger invasions.

Our results demonstrate that Legionella colonies on solid culture media are a good model of static biofilm with a complex structural dynamics characterized by the presence of morphological and functional subpopulations. We bring here an histological approach model, allowing, in further research, detailed studies in evolutionary adaptations in multicellular communities to adverse media and to antimicrobials in Legionella species of clinical interest.