Abstract
Three strains of Aerococcus viridans isolated from cases of acute meningitis and two older culture-collection strains have been studied for properties which may be associated with bacterial virulence. None produced extracellular polysaccharide in sucrose-trypticase soy broth, nor were they adherent to human buccal epithelial, HeLa, MRC5 or HEP2 cells. Ultrastructural examination revealed a ‘fuzzy layer’ of indistinct morphology, 10–15 nm thick and 75–150 nm ‘hairs’ or fibrils; the distribution of both layers was uneven on the cell wall. The ‘hairs’ were not removed but became less distinct on treatment with 0.1 per cent trypsin; the ‘fuzzy’ layer was unaffected. The three meningitis strains, but not the older strains, showed haemagglutinating activity on red cells at 37°C with no action on sheep, ox, human (group O), fowl, guinea-pig or monkey red cells; rabbit and mouse cells gave inconclusive results. The haemagglutin-ation of rat cells did not occur at 4°C or with heated (100°C, 10 min) or trypsinised (01 per cent) bacteria; it was inhibited by anti-A.viridans serum or normal serum, 0.5 per cent formaldehyde and unheated or heated (100°C, 10 min) mucin. Haemagglutination was unaffected by the presence of glucose, fructose, galactose, mannose, rhamnose, arabinose, xylose or fucose. Neuraminidase treatment of red cells appeared to inhibit the haemagglutination but treatment of bacteria with N-acetylneuraminic acid gave inconsistent effects. The strains showed a wide range of reactions from hydrophobic to hydrophilic, low hydrophobicity being more marked with the older strains.