rRNA gene restriction patterns of Streptococcus pyogenes: epidemiological applications and relation to serotypes

The use of rRNA gene restriction fragment length polymorphism analysis (ribotyping) to subtype Streptococcus pyogenes strains was investigated. Sixty-eight S. pyogenes strains, including 17 reference strains and 51 isolates from blood, acute or chronic pharyngitis, and food-borne outbreaks, were characterized by determination of both their rDNA restriction fragment length polymorphism profiles and their serotypes (T and M). Total DNA was cleaved with five selected restriction enzymes and then probed with a digoxigenin-labeled stretch of 1,063 bp hybridizing with 16S rRNA genes. Fifteen and nine distinct patterns were generated with SacI and XhoI, respectively, and five patterns were generated with each of the three additional restriction enzymes. With the combination SacI-XhoI, a total of 21 distinct ribotypes were obtained among the 68 isolates. This number was not increased by the results obtained with the other restriction enzymes. All strains tested were typeable. All isolates from each food-borne outbreak belonged to the same ribotype, and all isolates (pre- and posttreatment) from each child with chronic pharyngitis also belonged to the same ribotype, suggesting antibiotic treatment failures. A discriminatory index was calculated for the 47 isolates which were epidemiologically unrelated, using the Hunter-Gaston formula. This index reached 0.955 when the combination SacI-XhoI was used, showing the good discriminatory power of this typing method. Therefore, ribotyping proved to be a molecular method of interest to subtype S. pyogenes. Moreover, there was some correlation between ribotyping and serotyping, as several ribotypes were related to a unique distinct M serotype.