Pulsed field gel electrophoresis for molecular epidemiology of penicillin resistant Streptococcus pneumoniae strains

The emergence of strains of Streptococcus pneumoniae resistant to penicillin and other antibiotics has become a major concern for antimicrobial therapy of pneumococcal infections. The spread of that resistance over the world increases the need for their epidemiological surveillance: specific epidemiological markers are required. In this study, pulsed field gel electrophoresis of genomic DNA was carried out on sixteen resistant isolates of S. pneumoniae from different parts of the world and fifteen resistant isolates from Toulouse. The restriction endonucleases ApaI and SmaI were used to digest intact chromosomes and the fragments were resolved by field inversion gel electrophoresis (FIGE). Each digest produced 10 to 19 fragments for comparison between strains. The polymorphism obtained with FIGE was greater than that obtained with serotyping which appeared to be not a good criterion for genetic relatedness. Three common clones could be recognized among the penicillin-resistant isolates. Two clones were found in Spain and in Toulouse and were associated with serotypes 6B and 9V, respectively. The third clone was isolated in South Africa and in Spain and contained serotype 23F isolates and one serotype 19F strain. The FIGE profiles observed in this study also demonstrated that serogroup 23 multiresistant strains isolated in Toulouse are genetically closely related and might have originated from the same Spanish 23F clone. These results underline the importance of the geographic spread of resistant clones in the increase in the incidence of penicillin-resistant pneumococci. They indicate that pulsed field gel electrophoresis should be an effective tool for the typing of resistant S. pneumoniae strains capable of tracing their origin.