MUC5AC and cystic fibrosis: Additionally, the growth conditions for bacterial pathogens in the CF lung are markedly different due to the presence of viscous mucus, comprising breakdown products of inflammatory and epithelial cells, including copolymers of DNA and filamentous (F) actin, bacteria, cell debris, and variable amounts of mucin (63, 64), which also serve as nutritional sources for these pathogens (65).