Suppression of Protein A Production Decreases the Resistance of Staphylococcus aureus to the Bactericidal Effect of H2O2

Using several strains of Staphylococcus aureus, the resistance to the bactericidal effect of H202 was investigated. The protein A production in the bacteria of Cowan I, Smith and 209P strains which are capable to produce protein A on BHIA could be effectively suppressed by the cultivation on MSA. The viability of the bacteria which suppressed the protein A production was decreased by the incubation with H202. The protein A deficient Wood 46 strain did not show any difference in survival rate between those grown on BHIA and MSA. These results suggested that protein A was related to the resistance to the bactericidal effect of H202

A Comparative Study on the Resistance of Protein A-deficient Mutant and Cowan I Strains of Staphylococcus aureus to Hydrogen Peroxide in Vitro

A protein A-deficient strain, HL-87, was isolated from Staphylococcus aureus (S. aureus) Cowan I strain possessing protein A. Using the two strains, Cowan I and HL-87, the resistance to the bactericidal effect of hydrogen peroxide (H202) in vitro was investigated. It has been revealed that the viability of HL-87 strain was significantly lower than that of Cowan I strain after incubation in the presence of H202. When the catalase activity in both strains was assayed, HL-87 strain showed higher activity than Cowan I strain did, indicating that the difference in the resistance to in vitro H202 between the two strains did not depend on their catalase activity. These results suggested that protein A in the cell walls of Cowan I strain was directly related to the protection from the H202-bactericidal effect

Hydrophobicity of Streptococcus pyogenes is Responsible for the Phagocytic Reaction of Human Phagocytes

Stimulation of the phagocytic response of human phagocytes depends on the surface properties of bacteria. We studied what properties of Streptococcus pyogenes stimulate a phagocytic reaction, focusing on hydrophobicity and the Fc receptor. From Fc receptor-positive hydrophobic parent streptococcus, hydrophilic mutant and Fc receptor-deficient mutants were isolated. The mutant and parent strains were tested for stimulating activity for phagocytosis by measuring the chemiluminescence (CL) response of human phagocytes. The phagocytic response caused by the hydrophilic strain was significantly lower than that of the hydrophobic parent; while no difference in the stimulation of the phagocytic response was observed between Fc receptor-positive and -negative strains. These results showed that the hydrophobicity of the cell surface is responsible for the stimulation of the phagocytic response

GlmS and NagB Regulate Amino Sugar Metabolism in Opposing Directions and Affect Streptococcus mutans Virulence

Streptococcus mutans is a cariogenic pathogen that produces an extracellular polysaccharide (glucan) from dietary sugars, which allows it to establish a reproductive niche and secrete acids that degrade tooth enamel. While two enzymes (GlmS and NagB) are known to be key factors affecting the entrance of amino sugars into glycolysis and cell wall synthesis in several other bacteria, their roles in S. mutans remain unclear. Therefore, we investigated the roles of GlmS and NagB in S. mutans sugar metabolism and determined whether they have an effect on virulence. NagB expression increased in the presence of GlcNAc while GlmS expression decreased, suggesting that the regulation of these enzymes, which functionally oppose one another, is dependent on the concentration of environmental GlcNAc. A glmS-inactivated mutant could not grow in the absence of GlcNAc, while nagB-inactivated mutant growth was decreased in the presence of GlcNAc. Also, nagB inactivation was found to decrease the expression of virulence factors, including cell-surface protein antigen and glucosyltransferase, and to decrease biofilm formation and saliva-induced S. mutans aggregation, while glmS inactivation had the opposite effects on virulence factor expression and bacterial aggregation. Our results suggest that GlmS and NagB function in sugar metabolism in opposing directions, increasing and decreasing S. mutans virulence, respectively