Adhesion of C. diphtheriae strains to D562 cell layers. D562 cells were infected with different C. diphtheriae strains. Besides DSM43989, which is tox+, the isolates are non-toxigenic. The cells were washed with PBS, detached with trypsin solution, lysed with Tween 20, and the number of colony forming units (cfus) was determined. Adhesion is expressed as percentage of the inoculum, showing means and standard deviations of ten independent measurements (biological replicates) with 3 samples each (technical replicates). All strains, except ISS4746 and ISS4749, show statistically significant differences in adhesion rates (students TTEST values below 0.04).