Streptococcus pneumoniae colonizes the mucin-rich environment of the nasopharynx. As colonization may be the first stage of infection, investigation was carried out as to whether the pneumococcus could utilize mucin as a source of nutrient and whether its virulence gene expression is influenced by this glycoprotein. It was found that when grown in Sicard's defined medium supplemented with 1% w/v mucin, the organism grew at a rate similar to that in rich medium. The presence of sialate O-acetylesterase activity, an enzyme implicated in glycoprotein degradation, in pneumococcal cell extracts was also reported. The authors hypothesized that neuraminidase A, which is linked to pneumococcal virulence, plays an important role in mucin utilization. Growth in mucin resulted in an increase in nanA transcription and a DeltananA-deficient strain of pneumococcus could not grow when mucin was used as the sole carbon source.