7). Deduced from these PCR experiments, these genes seem to be absent in the investigated C. diphtheriae strains. As an additional approach, we tested expression of SpaD in the different strains by Western blot experiments. Cell extracts of strains ISS3319, ISS4040, ISS4746, ISS4749, DSM43988, DSM43989, and DSM44123 as well as purified SpaD protein as a positive control were separated

by SDS-PAGE and subjected to Western blotting. SpaD-specific antiserum reacted exclusively with the SpaD control, while no signal was detectable in the investigated cell extracts (data not shown). Figure 7 PCR detection of spa genes in C. diphtheriae strain NCTC 13129. Chromosomal DNA of C. diphtheriae strain NCTC 13129 was used as template for PCR using specific oligonucleotide pairs for the indicated spa genes. In all cases, DNA fragments of the expected size Selleckchem Ferroptosis inhibitor were amplified. To address the hypothesis that pili expression patterns might change, when bacteria were in exposed to host cells, Green fluorescent protein (GFP) fluorescence of C. diphtheriae transformed with plasmids carrying spa gene upstream DNA and Temsirolimus a promoter-less gfpuv gene

was determined without and after 1.5 h of host cell contact. However, analysis of 80 to 140 bacteria for GFP fluorescence before and after host cell contact revealed no significant differences (data not shown). Discussion In this study, different non-toxigenic C. diphtheriae and a toxin-producing strain were characterized in respect to adhesion to and invasion of epithelial cells. All strains were able to attach to host cells and immuno-fluorescence microscopy revealed internalization and growth of C. diphtheriae within epithelial cells. We could show that adhesion and invasion are not strictly coupled, indicating that different proteins and mechanisms play a role in these processes. Despite the fact

that the number of internalized ADAMTS5 bacteria decreased over time for all investigated strains, a considerable number of bacteria survived prolonged internalization for more than 18 h. Furthermore, V-shaped division forms as well as formation of microcolonies were observed by fluorescence microscopy, suggesting that the epithelial cells might support growth of C. diphtheriae. While proteins responsible for invasion and intracellular persistence are completely unknown for C. diphtheriae, for the sequenced strain NCTC13129 the influence of pili subunits on adhesion was characterized recently. It was shown that the minor pili subunits SpaB and SpaC are crucial for adhesion of strain NCTC13129 to epithelial cells [13], while pili length is influenced by the major pili subunits SpaA, SpaD, and SpaH, which form the shaft of the structure [11, 12, 19].