Electron microscopy study of the mode of growth of Pseudomonas pseudomallei in vitro and in vivo.

The mode of growth of Pseudomonas pseudomallei in culture media and in the lung tissue of infected humans and animals was studied using transmission electron microscopy (TEM) and scanning electron microscopy (SEM). In culture media, P. pseudomallei cells were seen to be entrapped in microcolonies within large amounts of intercellular fibrous material. The lung tissue of infected humans and animals showed that bacterial cells growing in lung tissue were surrounded by radially arranged fibres that constitute a very well defined glycocalyx structure. In the infected areas of the animal lung tissue, bacterial cell could be seen to have formed glycocalyx enclosed microcolonies that displaced host cell components, e.g. the nucleus of a phagocyte. The presence of bacteria in unusual locations indicated that effective phagocytosis was not occurring. The demonstration that cells of P. pseudomallei produce exopolysaccharide glycocalyces and form glycocalyx enclosed microcolonies in laboratory media and in lung tissue of infected humans and animals and the presence of bacteria in unusual locations contribute to a new understanding of the mechanism whereby this organism can cause persistent chronic infections.