[Serotypes, genotypes and drug resistance of group A streptococcal strains isolated in 1991, 2001 and 2002 in Tokushima Prefecture--comparison after decade].

Sixty two strains of Group A streptococcus were isolated between August 2001 and June 2002. They were examined for T serotypes, pyrogenic exotoxin genes and resistance against antibiotics. The results were compared with those for 61 isolates of the same species collected between April and December 1991. Among the strains isolated in 1991, T4 was the dominant serotype (18 strains) followed by T12 and T1 (each 15 strains). These three serotypes represented 78.7% of the total number. In contrast, among the strains isolated in 2001 and 2002 T28 (13 strains) was the dominant serotype followed by T1 (12 strains) and T4 (7 strains). Examination of these isolates for pyrogenic exotoxin gene revealed that all carried speB and more than half of the strains isolated in 1991, 2001 and 2002 carried both speB and speC. Regarding the combination of T type and toxin genotype, out of the isolates in 1991 fifteen T4 strains were associated with B and C, eleven T12 types with B and C, and nine T1 strains with A and B, while out of the strains isolated in 2001 and 2002 eleven T28 strains were associated with B and C, six T1 strains with B and C, and both five T4 and T12 types with B and C. Sma I Pulsed-field gel electrophorasis analysis revealed that PFGE patterns of T4:spe B and C and T12:spe B and C strains in 2001 and 2002 are same as one of those in 1991, respectively. On the other hand, during the decade strains resistant to macrolide increased from 1 strain (1.6%) to 11 strains (17.7%) and those to tetracycline increased from 23 strains (37.7%) to 32 strains (41.6%). During the same period the incidence of multiple resistance increased from 9 strains (14.7%) to 14 strains (22.5%).

Genetic studies on reference strains of mutans streptococci.

Twenty four reference strains (serotype a-h) belonging to the mutans group of streptococci were compared for DNA fragment patterns of rDNA after treatment with Hind III. It was shown that Streptococcus cricetus (serotype a), S. rattus (serotype b), and S. downei (serotype h) reveals comparatively homogeneous patterns while S. mutans (serotype c, e and f) exhibits differences between the different serotypes as well as within single serotypes. S. sobrinus had an intermediary diversity. These data support the previous findings that S. mutans is heterogeneous at the serological, biochemical and genetical level.