Evaluation of methods for epidemiologic typing of group A streptococci

Serotyping is widely used for epidemiologic investigation of group A streptococci (GAS). To evaluate molecular typing methods of GAS, restriction endonuclease analysis (REA) of genomic DNA and analysis of DNA restriction fragment length polymorphism of rRNA genes (ribotyping) were used in parallel with serotyping. The genomic DNA of 239 epidemiologically unrelated GAS isolates from human invasive infections was digested with HindIII restriction enzyme. Both REA and ribotyping differentiated subclasses within serotypes. However, they did not consistently differentiate between isolates of different serotypes. Ribotyping was less discriminatory than REA. Within the T1M1 serotype, often associated with invasive GAS infections, 92% of the REA patterns were identical, suggesting a common origin for these isolates. Most other serotypes studied were more heterogenic. Among 32 isolates nontypeable by serotyping, 11 distinct REA patterns and 5 ribotypes were identified. REA and ribotyping are useful supplementary tools for classification of GAS and can add to the discriminatory power of serotyping.