Metabolic utilisation 0f ManNAc and NeuNAc by S. gordonii, S. mitis and S. pneumoniae . S. gordonii V288 (A), S. pneumoniae G54 (B), and S. mitis NCTC12661 (C) were grown in CAT medium (200 U catalase) supplemented with 2 g/L glucose (black line) 2 g/L ManNAc (red line) and 1.5 g/L NeuNAc (blue line). CAT medium alone as a source of carbon is in grey line. All strains were grown for 38 hours at 37°C in 200 μl of medium in a 96 well microplate with reading intervals of 10 min. For the fermentation assay (panel D) bacteria were incubated for 24 and 48 h with serial dilutions of either ManNAc (left columns) or NeuNAc (right columns) as sole carbon sources in microtiter plates containing phenol red as a pH indicator. Sugar fermentation is evidenced by a yellow colour change due to acidification of the culture medium. Carbohydrate concentrations (% w/v) are shown on the right.