Bacteroides gingivalis W50 was grown in a chemostat under steady-state conditions at pH 7.5 ± 0.2 and a constant growth rate of 6.9 h for periods of up to 6 weeks (146 bacterial generations) in a complex medium. Hemin was capable of limiting the growth of cells up to a concentration of approximately 0.5 ,ug/ml since higher concentrations of hemin did not increase cell yields; cells grew in the absence of exogenously added vitamin Kl. Only a limited number of amino acids was metabolized during growth, but because none of these was totally depleted, the limiting nutrient under hemin excess conditions was probably a peptide. A range of fermentation products was produced under all conditions of growth; higher concentrations of cytotoxic metabolites such as propionate and butyrate were formed under hemin excess conditions, although more ammonia was released under hemin limitation. When viewed by electron microscopy, cells grown under hemin limitation appeared to be either coccobacillary or short rods and possessed few fimbriae per cell, but large numbers of extracellular vesicles could be seen both surrounding the cell surface and free in the environment. In contrast, cells grown under hemin excess conditions were more commonly coccus shaped and were more heavily fimbriated but had fewer extracellular vesicles. Marked differences were found in the susceptibility of mice to infection with cells grown under different concentrations of hemin. Cells transferred to media without any added hemin were avirulent, whereas those grown under conditions of hemin limitation (0.33 and 0.40 ,ug/ml) produced a 20 and 50% mortality in mice, respectively. In contrast cells grown under hemin excess always caused 100% mortality in mice, although this virulence was dose dependent. When virulent, the bacteria caused an extensive, spreading infection with necrosis of the skin and subcutaneous tissues. Collagen disintegration was seen histologically, implying a role for collagenase production in the pathogenicity of these bacteria.

Survival and growth of Legionella pneumophila in both biofilm and planktonic phases were determined with a two-stage model system. The model used filter-sterilized tap water as the sole source of nutrient to culture a naturally occurring mixed population of microorganisms including virulent L. pneumophila. At 20°C, L. pneumophila accounted for a low proportion of biofilm flora on polybutylene and chlorinated polyvinyl chloride, but was absent from copper surfaces. The pathogen was most abundant on biofilms on plastics at 40°C, where it accounted for up to 50% of the total biofilm flora. Copper surfaces were inhibitory to total biofouling and included only low numbers of L. pneumophila organisms. The pathogen was able to survive in biofilms on the surface of the plastic materials at 50°C, but was absent from the copper surfaces at the same temperature. L. pneumophila could not be detected in the model system at 60°C. In the presence of copper surfaces, biofilms forming on adjacent control glass surfaces were found to incorporate copper ions which subsequently inhibited colonization of their surfaces. This work suggests that the use of copper tubing in water systems may help to limit the colonization of water systems by L. pneumophila.

A two-stage chemostat model of a plumbing system was developed, with tap water as the sole nutrient source. The model system was populated with a naturally occurring inoculum derived from an outbreak of Legionnaires' disease and containing Legionella pneumophila along with associated bacteria and protozoa. The model system was used to develop biofilms on the surfaces of a range of eight plumbing materials under controlled, reproducible conditions. The materials varied in their abilities to support biofilm development and the growth of L. pneumophila. Elastomeric surfaces had the most abundant biofilms supporting the highest numbers of L. pneumophila CFU; this was attributed to the leaching of nutrients for bacterial growth from the materials. No direct relationship existed between total biofouling and the numbers of L. pneumophila CFU.

No abstract

The organs of monkeys infected with Ebola haemorrhagic fever were examined by light and electron microscopy during the acute stage of the disease. The virus caused focal coagulative necrosis in the liver, spleen, kidney, lung and testis and widespread mild vascular damage. In the brain there was intense congestion, with erythrocyte 'sludging', but no inflammatory reaction. There was significant injury to the microvasculature in all organs. Virus replicated in endothelial cytoplasm causing focal necrosis, separation of tight junctions and detachment from basement membranes. These changes were associated with oedema and haemorrhage, but though contributing to the hypovolaemic shock were not sufficiently extensive to account for the severity of vascular collapse. Renal involvement was also clinically important. Some renal cellular injury was caused by direct virus invasion of glomerular endothelium and tubular epithelium, but much tubular damage was probably due to ischaemia resulting from thrombosis in the peritubular capillaries. The virus also replicated in lymphocytes and monocytes and in interstitial cells of the testis. Since particles were not found in seminiferous epithelium, the degeneration of spermatogonia and spermatocytes was probably secondary to ischaemia.