c-di-AMP signaling is a central factor in many Gram-positive bacteria regulating cell wall synthesis, potassium ion channels, DNA repair, and biofilm formation. c-di-AMP is also essential for cell growth, survival, and virulence of several well-known human pathogenic bacteria [1]. c-di-AMP combines with model antigens, such as OVA or β-Gal, acts as a potent mucosal adjuvant stimulating both humoral and cellular responses [4].