Properties of metabolic substances produced by group A streptococcus from a food-borne epidemic

Here we report a large food poisoning outbreak by Streptococcus pyogenes that occurred in Kanagawa, Japan, in July 2005. To compare cases of type T-B3264 (Chiba) and type T-28 (Tokyo) reported to date, we studied the properties and activity of the major virulence factors produced by Streptococcus pyogenes type T-25 (Kanagawa): hemolysin, cysteine protease streptococcal pyrogenic exotoxin B (SpeB), and NAD glycohydrolase (NADase). These virulence factors were also analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). The titer of hemolysin was 9 50% hemolytic dose (HD50) per milliliter (HD50/ml) for T-25, 173 HD50/ml for T-28, and 147 HD50/ml for T-B3264. The hemolytic titer of T-25 was very low compared with those of T-28 and T-B3264. Each hemolysin produced by the three strains was dependent on its reductant, and its properties differed among strains. The major hemolysin of T-25 was identified as streptolysin O (SLO), because cholesterol or γ-globulin, but not phospholipids, inhibited its hemolysis. In contrast, the major hemolysin of T-28 and T-B3264 was streptolysin S (SLS). Although the SpeB activity of T-25 (4.8 U/ml) was lower than that of T-B3264, its NADase activity (19.1 U) was the largest of the three strains. The conversion from the SpeB precursor to mature SpeB was confirmed by SDS-PAGE analysis of T-25 at 6 h of culture; no conversion was identified for T-28 and T-B3264 at 6 h. SpeB of T-25 was converted quickly, most likely because of the degradation of SLO by SpeB, thereby resulting in the very low hemolytic titer of T-25. These results suggest that the three strains have diverse properties and activities of major virulence factors. The specific interactions of these virulence factors are thought to be involved in the pathosis of these strains.