Genome Organization and Pathogenicity ofCorynebacterium diphtheriaeC7(−) and PW8 Strains

Abstract

Corynebacterium diphtheriae is the causative agent of diphtheria. In 2003, the complete genomic nucleotide sequence of an isolate (NCTC13129) from a large outbreak in the former Soviet Union was published, in which the presence of 13 putative pathogenicity islands (PAIs) was demonstrated. In contrast, earlier work on diphtheria mainly employed the C7(؊) strain for genetic analysis; therefore, current knowledge of the molecular genetics of the bacterium is limited to that strain. However, genomic information on the NCTC13129 strain has scarcely been compared to strain C7(؊). Another important C. diphtheriae strain is Park-Williams no. 8 (PW8), which has been the only major strain used in toxoid vaccine production and for which genomic information also is not available. Here, we show by comparative genomic hybridization that at least 37 regions from the reference genome, including 11 of the 13 PAIs, are considered to be absent in the C7(؊) genome. Despite this, the C7(؊) strain still retained signs of pathogenicity, showing a degree of adhesion to Detroit 562 cells, as well as the formation of and persistence in abscesses in animal skin comparable to that of the NCTC13129 strain. In contrast, the PW8 strain, suggested to lack 14 genomic regions, including 3 PAIs, exhibited more reduced signs of pathogenicity. These results, together with great diversity in the presence of the 37 genomic regions among various C. diphtheriae strains shown by PCR analyses, suggest great heterogeneity of this pathogen, not only in genome organization, but also in pathogenicity.

Pangenomic Study of Corynebacterium diphtheriae That Provides Insights into the Genomic Diversity of Pathogenic Isolates from Cases of Classical Diphtheria, Endocarditis, and Pneumonia

“…It is also noteworthy that C. diphtheriae PW8 contains a degenerated SpaD gene cluster with multiple intact and disrupted genes encoding SpaD, SpaE, and SpaF pilins and sortases SrtB and SrtE (Fig. 9), in addition to a SpaA locus with a disrupted spaC gene (31). Sequences of mobile DNA elements are also detected in the SpaD locus of C. diphtheriae PW8, suggesting horizontal gene transfer for gene duplication.…”

“…Mutations in the base pilin SpaB and the tip pilin SpaC of the SpaA-type pilus were shown to reduce the adhesive activity of C. diphtheriae (46). In C. diphtheriae PW8, the spaC gene is characterized by a frameshift mutation (31), and almost all genes of the complex SpaD pilus gene cluster of PW8 are apparently inactivated by transpositional integration of insertion sequences. However, factors other than pili can contribute to cell adhesion of C. diphtheriae, including members of the resuscitation-promoting factor-interacting protein family (DIP1281) and the cell wall-associated hydrolase family (DIP1621).…”

“…Since then, C. diphtheriae C7(␤) toxϩ has been used worldwide as a reference strain for genetic research on iron metabolism and the regulation of tox gene expression. An initial genome comparison of C. diphtheriae C7(Ϫ) and C. diphtheriae PW8 based on genomic hybridization showed remarkable differences in the distribution of predicted pathogenicity islands (PAIs) and provided the first insights into the diversity of clinical isolates (31).…”

“…Since 1923, a diphtheria toxoid vaccine has been produced from diphtheria toxin treated with formalin to inactivate the toxicity and to maintain the immunogenicity of the protein (34). C. diphtheriae PW8 and derivatives thereof are widely used for the initial production of diphtheria toxin by submerged fermentation, because of their ability to secrete large amounts of toxin into the culture supernatant (31,52). C. diphtheriae PW8 is lysogenized by corynephage toxϩ , which moderately differs in its restriction map from the common ␤ toxϩ phage (60).…”

The Genus Corynebacterium and Other Medically Relevant Coryneform-Like Bacteria

“…(iv) A specialized urease locus in C. urealyticum facilitates alkalization of urine and formation of struvite stones (47). (v) An intact, toxin-producing strain of C. diphtheriae has 11 more pathogenicity islands and 37 additional regions, compared with C7(Ϫ), a nontoxigenic strain of that species (26). Among medically relevant coryneforms, stress-responsive systems that regulated the biofilm phenotype have been characterized from a mucoid strain of Rothia mucilaginosa (54).…”