One characteristic of P. larvae is that it secretes highly active extracellular proteases during vegetative growth and infection (Dancer and Chantawannakul, 1997; Holst, 1946; Holst and Sturtevant, 1940; Hrabak and Martinek, 2007). It is tempting to speculate that some of these proteases are responsible for the disruption of the epithelial barrier integrity by degrading cell–cell and cell–matrix junctional structures thereby allowing P. larvae to invade the hemocoel. Proteases are further needed by P. larvae for the subsequent degradation of the larval remains to a brownish, semi-fluid, glue-like colloid (ropy stage). Both processes are vital for P. larvae since it must somehow escape the larval integument while still in the vegetative stage to ensure that after sporulation the spores are freely accessible for being distributed in the bee colony and swallowed by the next host. The ropy stage (Figs. 2–4) dries down to a hard scale (foulbrood scale) tightly adhering to the lower cell wall. These scales are highly infectious since they contain millions of spores which drive disease transmission within and between colonies