Multilocus sequence typing identifies evidence for recombination and two distinct lineages of Corynebacterium diphtheriae

Abstract

We describe the development of a multilocus sequence typing (MLST) scheme for Corynebacterium diphtheriae, the causative agent of the potentially fatal upper respiratory disease diphtheria. Global changes in diphtheria epidemiology are highlighted by the recent epidemic in the former Soviet Union (FSU) and also by the emergence of nontoxigenic strains causing atypical disease. Although numerous techniques have been developed to characterize C. diphtheriae, their use is hindered by limited portability and, in some instances, poor reproducibility. One hundred fifty isolates from 18 countries and encompassing a period of 50 years were analyzed by multilocus sequence typing (MLST). Strain discrimination was in accordance with previous ribotyping data, and clonal complexes associated with disease outbreaks were clearly identified by MLST. The data produced are portable, reproducible, and unambiguous. The MLST scheme described provides a valuable tool for monitoring and characterizing endemic and epidemic C. diphtheriae strains. Furthermore, multilocus sequence analysis of the nucleotide data reveals two distinct lineages within the population of C. diphtheriae examined, one of which is composed exclusively of biotype belfanti isolates and the other of multiple biotypes.

FIG. 1.

Genetic relationships between the 73 sequence types identified and their relationship to ribotyping results. Where available, ribotyping data and the number of each ribotyped isolate are shown in italics to the right of the ST to which the ribotype corresponded. ST-59 (identified by an asterisk) refers to equine isolates 130 and 132. Lineage I and lineage II are highlighted by the line to the right of the phylogenetic tree.

FIG. 2.

Splits decomposition analysis illustrating the population structure within C. diphtheriae. (a) Splits within 8 STs from lineage I. (b) Relationship between representative STs from lineages I and II.