Comparison of four molecular typing methods for characterisation of Corynebacterium. diphtheriae: transcontinental spread of C. diphtheriae based on BstEII rRNA gene profiles

The diphtheria epidemic in the Russian Federation in the 1990's made diphtheria a focus of global concern once again. Development of rapid and reproducible typing methods for molecular characterisation of Corynebacterium diphtheriae has become a priority in order to be able to monitor the spread of this important pathogen on a global scale. We report the comparison of four molecular typing methods (ribotyping, pulsed field gel electrophoresis (PFGE), random amplification of polymorphic DNA (RAPD) and amplified fragment length polymorphism (AFLP) for the strain characterisation of C. diphtheriae. Initially, 755 isolates originating from 26 countries were analysed by ribotyping. One strain of each ribotype was then chosen randomly and characterised by PFGE, RAPD and AFLP. In order to ascertain whether the Eastern European epidemic ribotype could be further discriminated, 10 strains of ribotype D1 (the epidemic ribotype) were chosen randomly from different geographical regions and subjected to analysis by PFGE, RAPD and AFLP. The results revealed that ribotyping is highly discriminatory, reproducible and currently the method of choice for typing C. diphtheriae. PFGE and AFLP were less discriminatory than ribotyping and RAPD. An assessment of transcontinental spread of the organism showed that several genotypes of C. diphtheriae circulated in different continents of the world and each outbreak was caused by a distinct clone. Ribotypes seen in Europe appeared to be distinct from those seen elsewhere and certain ribotypes appeared to be unique to particular countries.