Fermentation by Streptococcus and anaerobic bacteria has been demonstrated before in CF lung secretions.24, 54 This hypothesis is supported by a recent study showing that anaerobic bacteria, first metabolize the sugar component of the mucin polypeptide in CF mucus, before P. aeruginosa can subsequently break down its amino acid component.80 This evidence concerns the gene MUC5AC and cystic fibrosis.