Diphtheria toxin (tox) and its regulatory element (dtxR) from 72 Corynebacterium 
diphtheriae strains isolated in Russia and Ukraine before and during the current 
diphtheria epidemic were studied by PCR-single-strand conformation polymorphism 
analysis (PCR-SSCP). Twelve sets of primers were constructed (eight for tox and 
four for dtxR), and three regions within tox and all four regions of dtxR showed 
significant variations in the number and/or sizes of the amplicons. Two to four 
different SSCP patterns were identified in each of the variable regions; 
subsequently, tox and dtxR could be classified into 6 and 12 different types, 
respectively. The great majority of epidemic strains from both Russia and 
Ukraine had tox types 3 and 4, and only in a single preepidemic strain isolated 
in Russia were all eight tox regions identical to those of C. diphtheriae 
Park-Williams No. 8 (tox type 1). Epidemic strains from Ukraine can easily be 
identified by dtxR type 5, while the majority of the Russian epidemic strains 
have dtxR of types 2 and 8. No differences in the tox regions between mitis and 
gravis biotype strains were observed. However, dtxR types 2, 5, and 8 were 
identified only in the gravis biotype, and dtxR type 1 was characteristic for 
the mitis biotype strains. PCR-SSCP is a simple and rapid method for the 
identification of variable tox and dtxR regions that allows for the clear 
association of tox and dtxR types with strains of distinct temporal and/or 
geographic origins.