Pilus Gene Pool Variation and the Virulence of Corynebacterium diphtheriae Clinical Isolates during Infection of a Nematode

Abstract

c Toxigenic Corynebacterium diphtheriae strains cause diphtheria in humans. The toxigenic C. diphtheriae isolate NCTC13129 produces three distinct heterotrimeric pili that contain SpaA, SpaD, and SpaH, making up the shaft structure. The SpaA pili are known to mediate bacterial adherence to pharyngeal epithelial cells. However, to date little is known about the expression of different pili in various clinical isolates and their importance in bacterial pathogenesis. Here, we characterized a large collection of C. diphtheriae clinical isolates for their pilin gene pool by PCR and for the expression of the respective pilins by immunoblotting with antibodies against Spa pilins. Consistent with the role of a virulence factor, the SpaA-type pili were found to be prevalent among the isolates, and most significantly, corynebacterial adherence to pharyngeal epithelial cells was strictly correlated with isolates that were positive for the SpaA pili. By comparison, the isolates were heterogeneous for the presence of SpaD-and SpaHtype pili. Importantly, using Caenorhabditis elegans as a model host for infection, we show here that strain NCTC13129 rapidly killed the nematodes, the phenotype similar to isolates that were positive for toxin and all pilus types. In contrast, isogenic mutants of NCTC13129 lacking SpaA-type pili or devoid of toxin and SpaA pili exhibited delayed killing of nematodes with similar kinetics. Consistently, nontoxigenic or toxigenic isolates that lack one, two, or all three pilus types were also attenuated in virulence. This work signifies the important role of pili in corynebacterial pathogenesis and provides a simple host model to identify additional virulence factors.

A Type I Signal Peptidase Is Required for Pilus Assembly in the Gram-Positive, Biofilm-Forming Bacterium Actinomyces oris

“…Surface expression of A. oris tip proteins was quantified by whole-cell enzyme-linked immunosorbent assay (ELISA) as previously described, with some modifications (21,22). Briefly, mid-logphase cells of A. oris MG1 and isogenic mutant strains were harvested by centrifugation and washed twice with PBS.…”

Genome-wide comparison of toxigenic and non-toxigenicCorynebacterium diphtheriaeisolates identifies differences in the pan genomes between respiratory and cutaneous strains

“…The growing numbers of apparently non-toxigenic but potentially invasive C. diphtheriae isolates identified by diagnostic and public health laboratories in countries with low prevalence of diphtheria raises concerns about other virulence factors and population dynamics of the species. Since the publication of the first complete genome sequence of C. diphtheriae (4) the phylogeographical structure of this species and the role of iron-uptake systems, adhesions and fimbrial proteins in virulence have become key questions that need addressing (5). Furthermore, the re-emergence of potent toxigenic variants may emerge from local strains being lysogenized by a toxin gene carrying corynebacteriophage (6).…”

Characterization of DIP0733, a multi-functional virulence factor of Corynebacterium diphtheriae

“…elegans were established as simple surrogate model systems for the investigation of Cor. diphtheriae pathogenicity and virulence factors (Ott et al, 2012;Broadway et al, 2013).…”