HETEROGENEITY OF DIPHTHERIA-TOXIN GENE, TOX, AND ITS REGULATORY ELEMENT, DTXR, IN CORYNEBACTERIUM-DIPHTHERIAE STRAINS CAUSING EPIDEMIC DIPHTHERIA IN RUSSIA AND UKRAINE

Diphtheria toxin (fox) and its regulatory element (dtxR) from 72 Coryn ebacterium diphtheriae strains isolated in Russia and Ukraine before a nd during the current diphtheria epidemic were studied by PCR-single-s trand conformation polymorphism analysis (PCR-SSCP). Twelve sets of pr imers were constructed (eight for tox and four for dtxR), and three re gions within tox and all four regions of dtxR showed significant varia tions in the number and/or sizes of the amplicons. Two to four differe nt SSCP patterns were identified in each of the variable regions; subs equently, tox and dtxR could be classified into 6 and 12 different typ es, respectively. The great majority of epidemic strains from both Rus sia and Ukraine had tox types 3 and 4, and only in a single preepidemi c strain isolated in Russia were all eight tox regions identical to th ose of C. diphtheriae Park-Williams No. 8 (tox type 1). Epidemic strai ns from Ukraine can easily be identified by dtrR type 5, while the maj ority of the Russian epidemic strains have dtxR of types 2 and 8. No d ifferences in the tox regions between mitis and gravis biotype strains were observed, However, dtxR types 2, 5, and 8 were identified only i n the gravis biotype, and dtxR type 1 was characteristic for the mitis biotype strains. PCR-SSCP is a simple and rapid method for the identi fication of variable tox and dtxR regions that allows for the clear as sociation of tox and dtxR types with strains of distinct temporal and/ or geographic origins.