Stimulation of cytokine release and adhesion molecule expression by products of Viridans streptococci.

The viridans streptococci (VS) are associated with the development of a rapidly fulminant shock syndrome in neutropenic patients. A panel of 52 VS strains isolated from the blood of neutropenic patients was used to demonstrate the ability of culture supernatants and cell walls of VS to induce release of the proinflammatory cytokines tumor necrosis factor (TNF)-alpha, interleukin (IL)-1beta, and IL-8 from whole blood in a dose- and strain-dependent fashion. Intercellular adhesion molecule-1 was shown to be markedly up-regulated on endothelial cells after incubation with plasma from blood exposed to cell walls or culture supernatants.

The relative contributions of recombination and point mutation to the diversification of bacterial clones.

Low levels of recombination in bacterial species have often been inferred from the presence of linkage disequilibrium between the alleles at different loci in the population. However, significant linkage disequilibrium is inevitable in organisms that divide by binary fission, and recombinational replacements must be very frequent, compared to point mutation, to dissipate disequilibrium. Recent studies using data from multilocus sequence typing indicate that, in many species, recombinational replacements contribute more greatly to clonal diversification than do point mutations and, in some species, recombination has been sufficient to eliminate any phylogenetic signal from gene trees.