Bacterial pathogens developed several strategies to overcome defense systems of eukaryotic hosts. Within the infection process, they need to attach to and cross through epithelial layers, escape from the innate and adaptive immune response, and find a physiological niche to survive. One target to modulate the host-pathogen interaction in order to deceit pathogen resistance is the actin cytoskeleton and its regulators: the family of Rho GTPases. Some bacterial toxins catalyze a covalent modification of Rho GTPases to keep these molecular switches in a constitutive active or inactive state. This leads to rearrangement of the actin cytoskeleton. Toxin-treated cells show typical morphological changes depending on substrate specificity and action of the toxins. In this chapter, we discuss the classes of bacterial toxins based on their mode of action, their recombinant expression (specifically CNF1), intoxication and subsequent morphological changes of the actin cytoskeleton, and cell shape.