Properties of Metabolic Substance Produced by Group A Streptococcus from Two Food-borne Epidemic

We report the finding for two food-poisonins outbreaks occurring in Tokyo and Chiba in September 2003. Patients in the Tokyo outbreak suffered from fever varying widely from 35.9℃ to 39.4℃. Throat pain was predominant, accompanied by headache, cough, and joint pain. Patients in the Chiba outbreak suffered from malaise in addition to the above symptoms. To clarify the relationship between pathology and virulence factors, we studied the properties of hemolysins and proteases produced by the causative bacteria, Streptococcus pyogenes, specifically type T-28 in the Tokyo outbreak and type T-B3264 in the Chiba outbreak. The main S. pyogenes T serotypes isolated in 2003 were types T12, T1, T4, and T3, followed types T-28 and T-B3264. The hemolytic titer of hemolysins, which are metabolic, was 173HD50/mL for T-28 and 147HD50 /mL for T-B3264. Hemolysins produced by both strains did not depend on reducing agents and were not inhibited by γ-globulin or cholesterol, indicating the streptolysin S (SLS) rather than hemolysis inhibition by phospholipids. The fact that the titer increased slightly in the presence of reducing agents indicates that some amount of streptolysin O may also have been present. Protease production was four times greater for T-B3264 than for T-28. Proteases produced by both strains were similarly inhibited by sodium tetrathionate, iodoacetate, and normal serum. The outbreak infection was caused by infiltration of food-borne Streptococcus bacteria via the upper airway during eating. The primary cause of predominant throat pain was thought to be SLS cytotoxicity in the upper respiratory mucous membrane. This toxin was also thought to assist in Streptococcus bacteria infiltration and proliferation. Proteases produced by pathogenic bacteria were thought to have acted on the body as potent virulence factors.