The addition of mucin to the bacterial inoculum transformed the pneumonia model from non-lethal (0%) to uniformly lethal (100%), and it correlated with a statistically significant increase in the bacterial burden of the lungs 38 h after infection (6.50 ± 0.43 without mucin vs. 9.26 ± 0.19 log10 CFU/g with mucin; P = 0.04 by Mann–Whitney test). Here, MUC5AC is linked to infection.