Figure 4 Transepithelial STI571 resistance of polarized D562 monolayers grown on transwells. (A) Control experiments of cells, which were incubated without bacteria (open circles) and S. enterica serovar Typhimurium (open squares). (B) Incubation with C. diphtheriae strains DSM43989 (tox +, open stars), ISS4749 (inverted closed triangles), ISS4746 (closed triangles),

ISS4060 closed circles, ISS3319 (closed square), DSM43988 (closed hexagons), and DSM44123 (closed diamonds). Experiments were carried out independently at least thrice and typical results are shown. Overnight incubation of D562 cells with C. diphtheriae was tested as well. In this case, the Dulbecco’s modified Eagle’s medium had to be exchanged after 3 h with fresh medium to remove not adhered bacteria in order to selleck chemical avoid that the pH of the medium

dropped due to the bacterial metabolism leading to secondary detrimental effects. In contrast to short term incubation and to the non-toxigenic strains, long term measurement (Fig. 4B, overnight time point) of transepithelial resistance of cell monolayers infected with DSM43989 showed a significant effect, which might be caused by toxin production. Ultrastructural analysis of C. diphtheriae strains Since we suspected that the differences in adhesion might be the result of different surface structures, we started an ultrastructure analysis of selected C. diphtheriae. For this purpose, non-toxigenic strains as well as tox + strain DSM43989 were analyzed by atomic force microscopy selleck (Fig. 5A). With this technique, which allows imaging surfaces topography at high resolution, significant different macromolecular surface structures were found between the different investigated C. diphtheriae strains. While for ISS4060 and DSM43988 pili were not detectable at all, ISS3319 and DSM44123 revealed short, spike-like pili, ISS4746, ISS4749 and DSM43989

showed long, hair-like protrusions (Fig. 5A). Also the number of pili (counted from at least six specimens of each strain) differed significantly (5B). Interestingly, adhesion and pili formation were not coupled, since ISS3319, which revealed spike-like pile and ISS4060, cAMP lacking these, showed comparable adhesion rates, while ISS4746 and ISS4749 had different numbers of long hair-like pili but showed identical adhesion rates. Also no correlation between invasion and pili formation was found. Since strain-specific differences in pili formation have not been observed before, the background for this phenomenon was investigated in more detail in subsequent experiments. Figure 5 Ultrastructural analysis of the cell surface of C. diphtheriae strains. (A) Bacteria were fixed on glass slides by drying using compressed air. Atomic force microscopy was carried out under ambient laboratory conditions and operated in tapping mode. Scale bars: 500 nm.