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DNase B is a major nuclease and a possible virulence factor in Streptococcus pyogenes. The allelic diversity of streptococcal DNase B (sdaB) gene was investigated in 83 strains with 14 emmgenotypes. Of the 15 alleles identified, 11 alleles carried only synonymous nucleotide substitutions. On the other hand, 4 alleles had a non‐synonymous substitution other than synonymous substitutions, resulting in the substitution of a single amino acid. The distribution of each allele was generally emmgenotype‐specific. Only sdaB7was found in both emm2and emm4. The promoter region was highly conserved and DNase B protein was similarly expressed in all alleles.

We noted that eight outbreaks of Shigella sonneifrom an unknown source occurred sequentially in Aichi Prefecture, Japan, between October 1992‐June 1993. For comparative purposes we analyzed 53 outbreak‐related isolates of Shigella sonneiusing different subtyping methods and studied the epidemiology of the outbreaks. It appeared from our study that DNA‐based techniques such as plasmid typing and pulsed‐field gel electrophoresis (PFGE) were more useful tools for subtyping Shigella sonneithan colicin typing and the antimicrobial susceptibility test. Moreover, according to PFGE analysis, four genetically related isolates of Shigella sonneiwere responsible for the eight sequential outbreaks. To further investigate the epidemiology of outbreaks, 58 sporadic isolates of Shigella sonneifrom overseas travelers with shigellosis during the same period were also examined. We found that some sporadic isolates from travelers in Asia were genetically related to those of the outbreak‐related isolates, indicating that genetically related isolates prevailed in Asia during this period, probably because of the extensive movement of people or food.