Bacterial colonization on days 5 and 14 of infection was determined by plating homogenates of aseptically removed tracheas on BG agar and in parallel the production of mucus in the infected tracheas was visualized on formalin-fixed histological sections by anti-Muc5AC immunohistochemical detection of Muc5AC production and by Alcian blue staining for acidic mucopolysaccharides and sialomucins, respectively. Here, MUC5AC is linked to infection.